Tagged Diet and Nutrition

Sweetgreen Makes Healthful Fast Food — But Can You Afford It?

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Employees work the line at Sweetgreen, a chain restaurant that uses fresh ingredients from local farms to make fast food healthier, in Berkeley, Calif.

Employees work the line at Sweetgreen, a chain restaurant that uses fresh ingredients from local farms to make fast food healthier, in Berkeley, Calif.Credit Jason Henry for The New York Times

Healthful, fast and affordable food is the holy grail of the public health and nutrition community. A popular restaurant chain shows just how much of a challenge that is.

It began when three Georgetown University students were frustrated that they could not find a healthy fast-food restaurant near their campus. With money raised from family and friends, they started their own, renting a small storefront on M Street in Georgetown. The result was Sweetgreen, a restaurant that offered organic salads, wraps and frozen yogurt. Pretty soon, the daily line of lunchtime customers stretched out the door and around the corner.

Ten years later, the line is still there, but Sweetgreen has grown into a nationwide salad chain, with more than 40 locations. Sweetgreen is part of a small but growing breed of farm-to-table fast-food chains – like Chopt Creative Salad Company on the East Coast and Tender Greens in California – that are giving fast-food restaurants a plant-based makeover. Their mission: to fix fast food, which has long been fattening and heavily processed.

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At Sweetgreen, fresh vegetables, cheeses and other ingredients are shipped directly to each restaurant from nearby farms and then chopped or cooked on site.

At Sweetgreen, fresh vegetables, cheeses and other ingredients are shipped directly to each restaurant from nearby farms and then chopped or cooked on site.Credit Jason Henry for The New York Times

Sweetgreen’s owners say their goal is to offer customers foods made with nutritious, sustainable and locally grown ingredients. The company has decentralized its food sourcing and production. Fresh vegetables, cheeses and other ingredients are shipped directly to each restaurant from nearby farms and then chopped or cooked on site. They don’t sell soda or use refined sugar.
Sweetgreen expects to open another 20 stores in major cities around the country this year, and eventually to expand to places where experts say healthy, delicious fast food is needed most — low-income neighborhoods.

But while the chain has proven there is a big appetite for more healthful fast food, the goal of taking this concept to poor areas may be a distant reality. The company and other chains like it operate almost exclusively in affluent communities, far from the low-income food deserts where obesity is rampant and farmers’ markets and healthy food stores are scarce. And with salads that typically cost between $9 and $14, some question whether a healthful fast-food chain like Sweetgreen can ever be affordable for average Americans.

Maegan George, a Columbia University student who lives near a Sweetgreen, calculated that for the price of one Sweetgreen salad, she could buy the same ingredients in bulk at a local market and make several similar salads at home.

“I’m a first-generation student and I’m on full financial aid,” she said. “Sweetgreen is delicious and I enjoy it. But there’s no way I could afford to eat there on a regular basis.”

Jackie Hajdenberg, another Columbia student, wrote about the restaurant for the campus newspaper, The Spectator, earlier this year, lamenting that on a per calorie basis, a salad at Sweetgreen was three times the price of a Big Mac at McDonald’s.

“Sweetgreen has not only made it easier for people to make healthy decisions – it has also illustrated the unequal socioeconomic landscape of the world in which we live,” she wrote.

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Salad options at Sweetgreen change often, depending on what is available at local farms.

Salad options at Sweetgreen change often, depending on what is available at local farms.Credit Jason Henry for The New York Times

Sweetgreen says it prices its food so that it can compensate its suppliers and employees fairly, and that it expects nutritious fast food to become more affordable as the healthy food movement grows. Nicolas Jammet, a co-founder of Sweetgreen, said the company wants to serve lower-income customers, and has long-term plans to expand to low-income communities.

To get there, he said, the company will have to overcome hurdles involving its supply chain, the minimum wage and greater nutrition awareness and education among the public. For the past six years the company has been running a nutrition education program in schools that teaches children about healthier eating and locally grown food.

“It’s a long-term goal for us to be part of this larger systematic change that needs to happen,” he said. “But there are so many parts of this problem that need to be addressed.”

Mr. Jammet notes that the company was among the first to show that fast-food chains don’t need profits from soda and sugary drinks to succeed. He believes chains like Sweetgreen have caused a ripple effect throughout the fast-food industry.

In January, for example, Chick-fil-A unveiled a new kale, broccolini and nut “superfood” salad, responding to customer demands for “new tastes and healthier ways to eat in our restaurants.” McDonald’s is experimenting with kale salads, and Wendy’s is testing a spinach, chicken and quinoa salad.

“Companies like McDonald’s have more power to change the way that people eat than we do,” Mr. Jammet said. “We don’t see these companies as the enemy. We just have to force change on them.”

Public health experts say that such changes cannot come soon enough. A University of Toronto study recently showed that people have a higher risk of developing diabetes if they live in “food swamps” – an area with three or more fast-food restaurants and no healthy dining options.

Another study published in JAMA in June found that the percentage of Americans eating an unhealthy diet — high in sugar, refined grains, soft drinks and processed foods and low in fruits and vegetables — was on the decline, but the improvements in diet were much smaller for lower-income Americans.

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Customers wait in line at Sweetgreen in Berkeley, Calif.

Customers wait in line at Sweetgreen in Berkeley, Calif.Credit Jason Henry for The New York Times

Overall about twice as many people from poor households have poor diets compared to those at higher income levels.
Why is traditional fast food so cheap? One reason is the underlying infrastructure of the industry. Many of the ingredients, like the soy that’s turned into oil for deep fryers, or the the corn that’s fed to animals and used to make high-fructose corn syrup, begin with crops that are heavily subsidized by the government. To make their food economical, many traditional fast-food chains mass-produce their food in large factories, often stripping it of fiber and other nutrients that decrease its shelf life, while adding salt, sugar and other flavorings and preservatives.

Then they freeze and ship the processed components, like burger patties, bread, pickles and sauce, to their restaurants. There they are reheated and assembled, often with minimal effort, ensuring that a Big Mac in Seattle looks and tastes the same as a Big Mac in Charlotte, N.C.

By comparison, every Sweetgreen location has a chalkboard that lists the farms where its organic arugula, peaches, yogurt or blueberries are produced. As a result, the menus vary by location and by season. In Boston, Sweetgreen stores use New England Hubbard squash. In Los Angeles, the menu features a different variety of squash grown locally in California.

Those differences mean fresher, more nutritious ingredients, but ultimately costlier food for customers — one of the obstacles that Sweetgreen and other chains like it will have to overcome if they hope to make their food more accessible to all income brackets.
Marion Nestle, a professor of nutrition, food studies and public health at New York University and the author of “Food Politics,’’ says restaurants like Sweetgreen offer an encouraging, but imperfect, model for making fast food more healthful.

“What’s not to like?” she asks. “The cost, maybe, but for people who can afford it the quality is worth it. Next step: Moving the concept into low-income areas.”

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How the Government Supports Your Junk Food Habit

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Credit Fred R. Conrad for The New York Times

At a time when almost three-quarters of the country is overweight or obese, it comes as no surprise that junk foods are the largest source of calories in the American diet. Topping the list are grain-based desserts like cookies, doughnuts and granola bars. (Yes, granola bars are dessert.)

That’s according to data from the federal government, which says that breads, sugary drinks, pizza, pasta dishes and “dairy desserts” like ice cream are also among Americans’ top 10 sources of calories.

What do these foods have in common? They are largely the products of seven crops and farm foods — corn, soybeans, wheat, rice, sorghum, milk and meat — that are heavily subsidized by the federal government, ensuring that junk foods are cheap and plentiful, experts say.

Between 1995 and 2010, the government doled out $170 billion in agricultural subsidies to finance the production of these foods, the latter two in part through subsidies on feed grains. While many of these foods are not inherently unhealthy, only a small percentage of them are eaten as is. Most are used as feed for livestock, turned into biofuels or converted to cheap products and additives like corn sweeteners, industrial oils, processed meats and refined carbohydrates.

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Health advocates have long pointed out this seeming contradiction. While the federal government recommends that people fill half their plates with fruits and vegetables to help prevent obesity, only a small fraction of its subsidies actually support the production of fresh produce. The vast majority of agricultural subsidies go instead to commodity crops that are processed into many of the foods that are linked to the obesity crisis.

“The subsidies damage our country’s health and increase the medical costs that will ultimately need to be paid to treat the effects of the obesity epidemic,” a 2012 report from the U.S. Public Interest Research Group, a nonprofit consumer advocacy organization, concluded. “Taxpayers are paying for the privilege of making our country sick.”

Now federal health researchers have examined the relationship between metabolic disease and the consumption of federally subsidized foods.

The study, led by a team at the Centers for Disease Control and Prevention and published this month in JAMA Internal Medicine, looked at over 10,000 adults and the foods they reported eating in a typical day. Then the researchers split the subjects into groups according to the proportion of foods they ate that were derived from the seven major subsidized commodities.

After adjusting for age, sex, socioeconomic factors and other variables, the researchers found that those who had the highest consumption of federally subsidized foods had a 37 percent greater risk of being obese. They were also significantly more likely to have belly fat, abnormal cholesterol, and high levels of blood sugar and CRP, a marker of inflammation.

While the study does not prove cause and effect, its authors say that this strong association is consistent with other research showing that diets that are higher in subsidized foods tend to be poorer quality and more harmful to health.

“This tells us that the factors that influence the prices of our foods are an additional factor,” said Ed Gregg, chief of the epidemiology and statistics branch in the C.D.C.’s Division of Diabetes Translation. “We’re hoping that this information reaches policy makers and the people who influence how subsidies work.”

The subsidies program was started decades ago in part to support struggling farmers and to secure America’s food supply. Since 1995, the government has provided farmers with close to $300 billion in agricultural subsidies overall, which are included in the federal farm bill, along with money for nutrition initiatives like the federal food stamps program, known as SNAP. The farm bill is renewed by Congress every five years and is projected to cost $956 billion between 2014 and 2023.

But critics say the subsidies program no longer serves its original purpose. Instead of supporting small farmers who grow fruits, nuts and vegetables – which the government calls “specialty crops” — the program now primarily subsidizes large producers that churn out a handful of “commodity” crops that include grains, corn, sorghum and oilseeds like soybeans.

According to the Government Accountability Office, small “specialty” farms represent three-quarters of the country’s cropland but receive just 14 percent of government subsidies. Large agribusinesses that specialize in growing the major commodity crops represent 7 percent of the cropland and receive about half of all subsidies.

Previous versions of the farm bill even stipulated that farmers who took subsidies for commodity crops could not grow fruits and vegetables. If they did, they were penalized, said Caroline Franck, the co-author of a 2012 report in the Archives of Internal Medicine that explored the role of agricultural subsidies in obesity.

Ms. Franck, a research assistant at the Lady Davis Institute for Medical Research of the Jewish General Hospital, McGill University, said many factors influence what people choose to eat. While it’s difficult to argue that subsidies are a direct cause of obesity, they clearly play a role.

“I think it’s safe to say that what happens at the top of the food chain has an impact on what happens at the bottom,” she said. “Agricultural policies are just not aligned with public health goals.”

In part because of public pressure, the last farm bill, which was passed in 2014, allowed farmers who grow commodity crops to use 15 percent of their acreage to grow fruits, vegetables and other specialty crops. It provided support to organic farmers, including $100 million for research to improve organic production. And it funded a “healthy incentives” program that encourages food stamp recipients to consume more fruits and vegetables by increasing the value of food stamps that are used to buy fresh produce at retail stores or farmers’ markets.

Ms. Franck said that early results suggest that the program is increasing the amount of fresh produce people consume. But others are not so sanguine. Raj Patel, a research professor at the Lyndon B. Johnson School of Public Affairs at the University of Texas at Austin, said that the funding for fruits and vegetables in the most recent farm bill was “crumbs” compared to the billions in subsidies for commodity crops.

Dr. Patel said it was time for the federal government to adopt a “national food policy” like one that has been proposed by the Union of Concerned Scientists, a nonprofit advocacy group. Among other things, a national food policy would ensure that farm workers receive fair wages, that all Americans have access to healthy foods, and that the government’s nutrition recommendations and agricultural policies are aligned, he said.

“It would transition us away from the unhealthy consequences of the current industrial food policy,” he said. “I think there’s something very broken about the subsidy system.”

Cutting Sugar Rapidly Improves Heart Health Markers

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Obese children who cut sugar from their diets saw improvements in markers of heart disease after just nine days, a study in Atherosclerosis found.

For the study, researchers evaluated 37 children ages 9 to 18 who were obese and at high risk for heart disease and Type 2 diabetes. The children were given food and drinks totaling the same number of calories, fat, protein and carbohydrates as their typical diets.

The only change was their sugar intake: The researchers swapped foods high in added sugars, like pastries and sweetened yogurts, for options like bagels and pizza. This lowered dietary sugar from 28 percent to 10 percent, and fructose from 12 percent to 4 percent of total calories.

After nine days, the researchers found a 33 percent drop in triglycerides, a type of fat tied to heart disease; a 49 percent reduction in a protein called apoC-III that is tied to high triglyceride levels; and dramatic reductions in small, dense LDL cholesterol, a risk factor for heart disease.

Though this study is small and short-term, it builds on this group’s previous research implicating added sugars as a contributor to metabolic disorders and heart disease.

“Sugar calories are not like other carbohydrate calories,” said Dr. Robert Lustig, a co-author of the study and professor of pediatrics at Benioff Children’s Hospital at the University of California, San Francisco. “Without changing total carbohydrate, or fat, or protein, we were able to accomplish this enormous improvement in their cardiovascular risk factors,” unrelated to weight loss, he said.

An App to Deconstruct Your Food

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A screenshot of the Sage app.

A screenshot of the Sage app.Credit

Ever wondered how long you’d have to swim to burn off the calories in an organic peanut butter cup? Or how far the strawberries or burger on your plate traveled to get there?

For answers, ask the Sage Project, one of the latest of the food technology companies helping consumers navigate nutrition. While a number of food apps count calories and track eating habits, Sage goes beyond the food label to give customers additional information about additives and preservatives, how much sugar has been adding during processing or how far a food has traveled.

“Food labels are a data visualization that we see every day, but we don’t get a lot from them,” said Sam Slover, the co-founder and chief executive of Sage. “There are a lot of things about those labels that make assumptions about what you know and what you want to know.”

Do we really need another food app? Apple’s app store already lists more than three dozen apps offering users information and advice about calories, nutrition data and weight loss, but research shows that many consumers have a failed relationship with their food apps. For instance, in January, about 16 percent of the people who downloaded the Lose It app were using it once a day. By June, only 10 percent were using it that often, according to research firm 7Park Data.

“These apps have trouble keeping customers loyal — if you use them successfully, you don’t need them any more, and if you don’t use them successfully, you may not think it’s worth it to try more,” said Byrne Hobart, the lead analyst at 7Park Data. “They’re kind of like the dating apps that way.”

The Sage app hopes to inspire more loyalty by providing a trove of useful and quirky information about the food you eat. It contains data on about 20,000 products, though you still may not find your favorite junk foods. Most of the products in the database are described as “natural” and “organic.” But if you shop at Whole Foods, you’re in luck. Sage has partnered with Whole Foods Market, deconstructing all of the roughly 7,000 items sold in the grocer’s new “365” store chains in Los Angeles and Lake Oswego, Ore.

To begin using Sage, which is available online or as a web-based app, a user signs up and enters any food restrictions and personal preferences. Only want to see products without additives and preservatives? No problem. Interested in digestive health? Sage will comb through its database and show you products with probiotics, high fiber and whole grains.

The app displays a wide variety of information using colorful graphics and animated food characters, and it’s surprisingly fun and entertaining to use. The app told me that Surf Sweet gummy bears, for instance, do have a fair amount of added sugar but also have “good nutrient density,” meaning that, among other things, they supply a high amount of vitamin C (much to my delight). A jump-roping chocolate bar informs me that I’d need to jump rope for 19 minutes — or a snorkeling olive recommends 23 minutes of swimming — to burn off a serving of Justin’s Organic milk chocolate peanut butter cups.

“Customers want a better understanding of how a product is sourced, the quality standards behind it, whether the labor that made it was paid a fair wage, its impact on the environment,” said Jason Buechel, the chief information officer at Whole Foods. “This is a way to give them all that information that isn’t captured on the nutrition label.”

Take the Beast Burger, for instance, a meatless burger sold at Whole Foods. Type the name of the burger into Sage or flip through a list, and you’ll find its basic nutritional profile and calorie content, with highlights of its nutritional strengths.

Using animated food characters — a pear doing yoga, a watermelon riding a bike — the app shows how much exercise would be required to work off the burger. In my case, it’s 20 minutes of running, 22 minutes of jumping rope, 28 minutes of swimming or biking, 44 minutes of dance or 89 minutes of yoga.

Sage also identifies any allergens — corn and seeds in the case of the Beast Burger — and offers detailed explanations of all the burger’s ingredients, and why they’re used should you be interested. For instance: “Calcium chloride, a salt, is used in canned goods to improve stability and quality and as a firming agent in tofu production.”

The system awards “badges” to the burger for things like an abundance of healthy fats and protein and having recyclable packaging, and it explains what diets — dairy free, gluten free, vegan, vegetarian and ketogenic — it does not violate. To make nutrition recommendations like “fiber friendly” or “heart healthy,” Sage uses nutritional standards set by the Food and Drug Administration and the American Heart Association. An in-house team of dietitians and nutritionists have created standards for badges like “healthy fats” or “contains probiotics” — areas where the F.D.A. doesn’t set guidelines.

Finally, the app tells you where the product is made or sourced. The Beast Burger is American made. If you decided to check out Driscoll strawberries, you might learn your batch came from Mexico.

It also can tailor daily nutritional requirements to a user’s specific weight, height and lifestyle. For instance, Sage came up with a recommended daily caloric intake of about 3,300 calories that is rich in protein for Mr. Slover, given his height, weight and exercise routine — he’s a triathlete. It recommended a 1,600-calorie diet with a lower portion of protein for his mother.

“All those things on a label telling you that a product gives you, say, 10 percent of the daily requirement of protein is based on a default, 2,000-calorie-day diet, a kind of one-size-fits-all approach that doesn’t work,” Mr. Slover said.

One thing the Sage app won’t tell you is what you should or shouldn’t eat. You will have to figure that out for yourself. “I’m not a big fan of red, yellow and green scoring mechanisms for food,” Mr. Slover said. “I don’t think they’re well received by consumers or used very much.”

No Health Benefit to Replacing Fat With Carbs

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Low-fat diets that are high in carbohydrates are unlikely to improve your health, a new study shows.

Researchers came to the conclusion after studying the eating habits and health behaviors of 126,233 men and women who completed health questionnaires every two to four years for up to 32 years. Then they calculated the effect of replacing just 5 percent of saturated fat calories with another type of fat or carbohydrates.

The study, in JAMA Internal Medicine, found that replacing 5 percent of daily calories from saturated fats (mainly animal fat) with foods high in monounsaturated fat, such as olive oil and avocados, was associated with a 27 percent reduction in total mortality and reduced death from cardiovascular disease, cancer and neurodegenerative disease.

A similar switch from saturated fat to polyunsaturated fats, such as the omega-3 and omega-6 fatty acids in fish and walnuts, was associated with a 13 percent reduction in total mortality and a 29 percent reduction in death from neurodegenerative diseases.

But replacing saturated fats with carbohydrates, such as sugars and refined grains, did not confer any health benefits.

“Not all fats are created equal,” said the senior author, Dr. Frank B. Hu, a professor of nutrition at the Harvard T.H. Chan School of Public Health. “We should eat more good ones from fish and avocados, instead of animal fats. And second, the low-fat, high-carbohydrate diet is not beneficial for improving health and longevity.”

Ask Well: Is Watermelon Good for You?

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Credit Karsten Moran for The New York Times

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Fat Dad: The Coffee and Cigarette Diet

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Credit Andrew Scrivani for The New York Times

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The author’s parents, summer-ready.

The author’s parents, summer-ready.Credit

My dad’s face lit up as he placed the engraved linen envelope on the table. We were to be guests at the annual pool party at his boss’s home in East Hampton, N.Y. Not only were we invited for dinner, we were invited to stay for the whole glorious weekend.

Our host was my dad’s boss at the McCann Erickson ad agency, where he was a new creative director. Getting an invitation to his house was more than a polite formality; it was an honor. His family lived on Park Avenue, summered in the Hamptons, and lived by the Emily Post school of etiquette. My family never summered anywhere. We didn’t dress for dinner, we didn’t play golf or tennis, and no one in my family had ever studied Latin or carried a monogrammed bag.

While my dad was flattered, the pressure that accompanied the invitation was huge. His weight had ballooned to almost 400 pounds since landing the job, thanks in part to the decadent three-course client lunches and late-night strategy dinners. In the office, people were focused on my dad’s marketing ideas, but in the Hamptons, my dad said appearances were everything, and there was no hiding behind his creative storyboards and well-thought-out campaigns. He would be presenting my mom, my little sister, April, and me, and showing himself in a more vulnerable setting.

The month leading up to the Hamptons trip was filled with anxiety. My mom and I rushed around shopping for the perfect outfits, and my dad, determined to fit into a bathing suit, starved himself, declaring he was on the “Super Model Diet,” which consisted of hot coffee, cold coffee, coffee shakes, coffee bread, unlimited cigarettes and water.

Even at 10 years old, I knew this was not healthy. I had read the many nutrition and diet books that filled every bookshelf in our house. Each week a new diet, a new promise for miracle results.

“All the actresses and dancers in my commercials swear by this one,” my dad said. “They say substituting a zero-calorie cigarette for lunch helps them stay camera-ready,” he added.

Seeing how worried I was, my dad declared he had never had so much energy, begging my sister and me to try to tag him while he ran up and down the halls of our apartment — not even tempted to take a peek at the diet bread I had just baked for him — adding the required three-quarters of a cup of coffee to my ingredient list.

After successfully losing over 20 pounds on the coffee and cigarette diet in a couple of weeks, my dad headed to Mr. Big & Tall on Eighth Avenue for a couple of items before picking up the Hertz Rent-a-Car. My dad was proud of his new lime-green Bermuda shorts with pictures of palm trees. As we drove to the Hamptons in our beach clothes, my parents argued because my mom, who was in charge of directions, kept navigating us the wrong way. When we finally made it off the highway, my parents became calmer, admiring the quaint churches, old houses and windmills planted on village greens.

Arriving hot and disheveled after our long drive, we were greeted by my father’s boss’s wife, who was wearing a neatly pressed blue Pucci cocktail dress, adorned with a single strand of pearls. Tucking her coiffed blond hair behind her ears, she offered us iced tea with orange slices and led us to the back yard. It was like no pool party I had ever been to, and I wondered if anyone was actually planning to swim.

The tables had crystal candlesticks, and waiters were passing around trays of delicious appetizers that I couldn’t pronounce. Among them were rumaki  — chicken livers wrapped with chestnuts — and soufflés — puffy omelets loaded with cream. There were plates stacked on top of plates and more silverware than I had ever seen. For dinner, we each had our own one-and-a-half-pound lobster with a side of mussels and white sweet corn from the local farm stand. The kids and the grown-ups were served the same food, but we were not seated at the same table. Parents and kids sitting together was a no-no, according to our host’s son, whom I was placed next to.

The boy, who was wearing a jacket and a tie, was only a year older than I was but had the demeanor of a grown man. When I asked, “Aren’t you hot in that stuffy outfit?” he said that the men in their family “always wear a tie and a blazer at dinner each and every night.” He motioned to me to unfold my napkin and place it over my bare legs, dangling above the ground.

I tried to follow his lead as I saw my dad covered in melted butter and lobster juice. He seemed to be enjoying himself immensely, not shy about asking for seconds and thirds of potatoes au gratin as he forfeited the salad and green beans. “I need to leave room for the good stuff,” he exclaimed, loosening his belt buckle, as the table howled in laughter, watching my dad joyfully dash to the dessert table.

“Go for the gusto, Lerman!” my dad’s boss bellowed, pleased that all the guests started chanting my dad’s award-winning slogan for Schlitz beer.

“You Only Go Around Once in Life, So Grab the Gusto,” they yelled out, encouraging my father to load and re-load his plate.

While I knew that the next day my dad would have regrets, and his vicious cycle of yo-yo dieting would begin again, that night I relaxed, savoring every bite of the succulent meat — hoping my first lobster dinner would not be my last.

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Swimsuit-Ready Iced Coffee Shake


Dawn Lerman is a Manhattan-based nutrition expert and the author of “My Fat Dad: A Memoir of Food, Love and Family, With Recipes,” from which this essay is adapted. Her series on growing up with a fat father appears occasionally on Well. Follow her @DawnLerman.

A Few More Vegetables and a Little Less Meat May Reduce Diabetes Risk

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Credit Justin Mott for The New York Times

You don’t have to be a vegetarian to reap the benefits of a plant-based diet.

New research shows that eating a few extra servings of healthy plant-based foods each day and slightly reducing animal-based foods like meat and dairy products can significantly lower your risk of Type 2 diabetes.

The findings are based on an analysis of the eating patterns of 200,000 men and women from three long-term studies who reported on their diets repeatedly over the course of two decades, and were published this week in PLOS Medicine.

The studies — the Nurses’ Health Study, the Nurses’ Health Study 2 and the Health Professionals Follow-Up Study — asked participants to fill out more than 100 detailed questions about their eating habits. They provided information not just about the foods they ate but about how the food was prepared and even what cooking oils were used.

While self-reported dietary information can be flawed, extra steps were taken to confirm the data. Participants completed questionnaires every two to four years, and the nutrient intake information was compared to tests of blood biomarkers to make sure they matched up. The results were also adjusted, or modified, to account for other characteristics that contribute to Type 2 diabetes, like being overweight.

The research was also unusual in that it distinguished between healthful and unhealthful plant-based foods. Healthful plant-based foods include whole grains, fruits, vegetables nuts, seed and legumes, while an unhealthful plant-based diet could include refined carbohydrates like bagels and muffins, starchy vegetables like potatoes and French fries and sugary foods like cake and cola. Animal-based foods include meat of all kinds, fish and seafood as well as eggs, dairy products and animal fats like butter.

On average, adults who ate a plant-based diet with few animal products cut their risk of Type 2 diabetes by 20 percent. But when researchers distinguished between healthful and unhealthful plant-based foods, they found that diabetes risk dropped by 34 percent among the healthful plant-based eaters. Notably, there wasn’t a benefit to plant-based eating when a person consumed a lot of refined carbohydrates and starchy vegetables. In that case, a person’s risk of developing Type 2 diabetes increased slightly.

While most American adults are omnivores, eating from many different food sources, and few are vegetarian, the research suggests that simply reducing the amount of animal-based food you eat from five or six servings a day to about four servings a day can lower the incidence of Type 2 diabetes. When people make these changes in diet, they usually cut back on red meat and processed meats and substitute healthier plant-based foods, including protein-rich ones like nuts, seeds and legumes, said Frank Hu, the study’s senior author and a professor at Harvard’s T.H. Chan School of Public Health.

“What we’re talking about is a moderate shift – replacing one or two servings of animal food a day with one or two plant-based foods,” said Dr. Hu. “We’re not talking about a dramatic change from being a carnivore to being vegan or even vegetarian – we’re talking about a small shift, that’s doable for most people. You can still include some meat, but not have it in the center of the plate.”

Good plant-based foods are known to be rich in fiber, antioxidants, good fats and a wide array of micronutrients, and have been shown to improve glucose metabolism and lower inflammatory markers. But scientists say they also help promote the good-for-you bacteria that live in your gut.

“When we ingest food, we’re feeding ourselves, but we’re also feeding the bacteria in our gut,” said Dr. Hu. “If you switch from an animal-based dietary pattern to a plant-based pattern, after a while – I don’t know how long it would take, a few weeks or months – the type of bacteria will also change.”

The bacteria in the gut use components of plant-based foods like fiber for their own survival and growth. These components are metabolized by the intestinal bacteria, and the end products are short-chain fatty acids, which have been shown to have beneficial effects on inflammation, insulin resistance and overall metabolism. They also may send a satiety signal to the brain, so people feel fuller.

When you eat refined carbohydrates and have less fiber in the diet, the healthy bacteria that metabolize fiber will be reduced, “so you won’t have the short-chain fatty acids that would have beneficial effects in your body,” Dr. Hu said.

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Parents Should Avoid Comments on a Child’s Weight

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Credit Stuart Bradford

Should parents talk to an overweight child about weight? Or should they just keep their mouths shut?

Parents in this situation are understandably torn. Say something, and they risk shaming a child or worse, triggering an eating disorder. Say nothing, and they worry they’re missing an opportunity to help their child with what could become a serious long-term health problem.

Now a new study offers some guidance: Don’t make comments about a child’s weight.

The study, published in the journal Eating & Weight Disorders, is one of many finding that parents’ careless — though usually well-meaning — comments about a child’s weight are often predictors of unhealthy dieting behaviors, binge eating and other eating disorders, and may inadvertently reinforce negative stereotypes about weight that children internalize. A parent’s comments on a daughter’s weight can have repercussions for years afterward, contributing to a young woman’s chronic dissatisfaction with her body – even if she is not overweight.

“Parents who have a child who’s identified as having obesity may be worried, but the way those concerns are discussed and communicated can be really damaging,” said Rebecca Puhl, deputy director of the Rudd Center for Food Policy and Obesity at the University of Connecticut. “The longitudinal research shows it can have a lasting impact.”

The impact on girls may be especially destructive, she said, because “girls are exposed to so many messages about thinness and body weight, and oftentimes women’s value is closely linked to their appearance. If parents don’t challenge those messages, they can be internalized.”

The new study included over 500 women in their 20s and early 30s who were asked questions about their body image and also asked to recall how often their parents commented about their weight. Whether the young women were overweight or not, those who recalled parents’ comments were much more likely to think they needed to lose 10 or 20 pounds, even when they weren’t overweight.

The study’s lead author, Dr. Brian Wansink, a professor and the director of Cornell University’s Food and Brand Lab, characterized the parents’ critical comments as having a “scarring influence.”

“We asked the women to recall how frequently parents commented, but the telling thing was that if they recalled it happening at all, it had as bad an influence as if it happened all the time,” said Dr. Wansink, author of the book “Slim by Design.” “A few comments were the same as commenting all the time. It seems to make a profound impression.”

Some studies have actually linked parents’ critical comments to an increased risk of obesity. One large government-funded study that followed thousands of 10-year-old girls found that, at the start of the study, nearly 60 percent of the girls said someone — a parent, sibling, teacher or peer – had told them they were “too fat.” By age 19, those who had been labeled “too fat” were more likely to be obese, regardless of whether they were heavy at age 10 or not.

Comments made by family members had even stronger effects than comments made by unrelated people.

Several studies have found that when parents encourage overweight teenagers to diet, the teenagers are at higher risk of lower self-esteem and depression and of being overweight five years later.

Research by Dianne Neumark-Sztainer, a professor at the University of Minnesota, found that when parents talked to their teens about losing weight, teenagers were more likely to diet, use unhealthy weight-control behaviors and binge eat. Those behaviors are less likely to develop when conversations with parents focused on healthy eating behaviors, rather than weight per se.

Harsh comments about weight can send the message that parents are “tying weight to some kind of perception about how the child is valued,” Dr. Puhl said, and that can trigger negative feelings. “The children are internalizing that, and thinking they’re not O.K. as a person. And that is what’s leading to other outcomes, like disordered eating.”

So what’s a parent to do? Do they just stand by while their child gains weight?

Dr. Neumark-Sztainer was besieged by parents asking her this question, and wondering, “How do I prevent them from getting overweight and still feel good about themselves?”

In her book, called “I’m, Like, SO Fat: Helping Your Teen Make Health Choices About Eating and Exercise in a Weight-Obsessed World,” she notes that parents can influence a child’s eating habits without talking about them. “I try to promote the idea of talking less and doing more — doing more to make your home a place where it’s easy to make healthy eating and physical activity choices, and talking less about weight.”

For parents, that means keeping healthy food in the house and not buying soda. It means sitting down to enjoy family dinners together, and also setting an example by being physically active and rallying the family to go for walks or bike rides together. Modeling also means not carping about your own weight. “Those actions speak louder than words,” Dr. Puhl said.

While your children are young, “there doesn’t need to be a conversation at all – it really is just about what’s being done at home,” Dr. Neumark-Sztainer said.

If an older child is overweight, “wait for your child to bring it up, and be there to support them when they do,” she said. “Say, ‘Look, I love you no matter what size you are, but if you would like, I will support you. I suggest we focus not so much on your weight but on your eating patterns and behaviors. What would be helpful for you?’”

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Eat Whole Grains, Live Longer?

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Credit Karsten Moran for The New York Times

Two large review studies have reached the same conclusion: Eating whole grains is associated with significant reductions in the risk for premature death.

One report, in BMJ, found that whole grain consumption was associated with a reduction in the risk for death from cancer, coronary heart disease, respiratory disease, infectious disease and diabetes. Using data from 45 studies, researchers calculated that compared with eating none, eating 90 grams of whole grains a day reduced the risk for all-cause mortality by 17 percent.

The other analysis, in Circulation, used data from 14 prospective studies with 786,076 participants and found that compared with those who ate the least whole grain foods, those who ate the most had a 16 percent reduced risk for all-cause mortality and an 18 percent reduced risk for cardiovascular mortality. Each 16-gram increase in whole grain intake reduced mortality risk by 7 percent.

A slice of 100 percent whole grain bread contains about 16 grams of whole grains, and current dietary guidelines recommend 48 grams or more of whole grains daily.

The senior author of the Circulation study, Dr. Qi Sun, an assistant professor of nutrition at Harvard, cautions that eating whole grains is not a panacea.

“You shouldn’t hope that you will cure diseases with whole grain foods,” he said. “You still have to pay attention to other good dietary and behavioral practices.”

Ask Well: Getting the Most Out of Whole Grains

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Is Sugar Really Bad for You? It Depends

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The federal government’s decision to update food labels last month marked a sea change for consumers: For the first time, beginning in 2018, nutrition labels will be required to list a breakdown of both the total sugars and the added sugars in packaged foods. But is sugar really that bad for you? And is the sugar added to foods really more harmful than the sugars found naturally in foods?

We spoke with some top scientists who study sugar and its effects on metabolic health to help answer some common questions about sugar. Here’s what they had to say.

Why are food labels being revised?

The shift came after years of urging by many nutrition experts, who say that excess sugar is a primary cause of obesity and heart disease, the leading killer of Americans. Many in the food industry opposed the emphasis on added sugars, arguing that the focus should be on calories rather than sugar. They say that highlighting added sugar on labels is unscientific, and that the sugar that occurs naturally in foods like fruits and vegetables is essentially no different than the sugar commonly added to packaged foods. But scientists say it is not that simple.

So, is added sugar different from the naturally occurring sugar in food?

It depends. Most sugars are essentially combinations of two molecules, glucose and fructose, in different ratios. The sugar in a fresh apple, for instance, is generally the same as the table sugar that might be added to homemade apple pie. Both are known technically as sucrose, and they are broken down in the intestine into glucose and fructose. Glucose can be metabolized by any cell in the body. But fructose is handled almost exclusively by the liver.

“Once you get to that point, the liver doesn’t know whether it came from fruit or not,” said Kimber Stanhope, a researcher at the University of California, Davis, who studies the effects of sugar on health.

The type of sugar that is often added to processed foods is high-fructose corn syrup, which is the food industry’s favored sweetener for everything from soft drinks to breads, sauces, snacks and salad dressings. Made commercially from cornstarch, high-fructose corn syrup is generally much cheaper than regular sugar. It contains the same components as table sugar – glucose and fructose – but in slightly different proportions.

What about “natural” sweeteners?

Food companies like to market agave nectar, beet sugar, evaporated cane juice and many other “natural” sweeteners as healthier alternatives to high-fructose corn syrup. But whatever their source, they are all very similar. To suggest one is healthier than another is a stretch, experts say. In fact, last month, the F.D.A. urged food companies to stop using the term evaporated cane juice because it is “false or misleading” and “does not reveal that the ingredient’s basic nature and characterizing properties are those of a sugar.”

Is high-fructose corn syrup worse than regular sugar? How is it different?

High-fructose corn syrup and regular sugar are so similar that most experts say their effects on the body are essentially the same.

The main difference is that the variety of high-fructose corn syrup used in soft drinks tends to have more fructose. In one 2014 study, researchers analyzed more than a dozen popular soft drinks and found that many sweetened with high-fructose corn syrup – including Pepsi, Sprite, Mountain Dew, Coca-Cola and Arizona Iced Tea – contained roughly 40 percent glucose and 60 percent fructose. Regular sugar contains equal parts glucose and fructose.

Why doesn’t the F.D.A. require that added sugars be listed in teaspoons rather than grams?

When the new food labels go into effect, the daily recommended limit for added sugars will be 50 grams, or roughly 12 teaspoons, daily. (One teaspoon of sugar is 4.2 grams.) But the new food labels will list the amount of added sugars solely in grams.

Many nutrition advocates have urged the F.D.A. to require that food labels list added sugars in both teaspoons and grams on food labels, arguing that Americans often underestimate the actual amount of sugar in a product when it’s expressed in grams alone.

But the F.D.A. ultimately sided with the food industry, which opposed the teaspoon proposal.

“It would be difficult, if not impossible, for a manufacturer to determine the volume contribution that each ingredient provides toward the added sugars declaration,” the agency said. “For example, a cookie made with white chocolate chips and dried fruit would have added sugars in the form of sugar in the batter as well as in the white chocolate chips and the dried fruit.” The F.D.A. also said that requiring both grams and teaspoons would “cause clutter and make the labels more difficult to read.”

But Michael Jacobson, the president of the Center for Science in the Public Interest, an advocacy group that had petitioned the F.D.A. to require the teaspoon measurement, said the agency was under enormous pressure from the food industry, “which knows that consumers would be far more concerned about a product labeled 10 teaspoons than 42 grams.”

So what’s the issue with added sugars?

It mainly comes down to the way they’re packaged.

Naturally occurring sugar is almost always found in foods that contain fiber, which slows the rate at which the sugar is digested and absorbed. (One exception to that rule is honey, which has no fiber.) Fiber also limits the amount of sugar you can consume in one sitting.

A medium apple contains about 19 grams of sugar and four grams of fiber, or roughly 20 percent of a day’s worth of fiber. Not many people would eat three apples at one time. But plenty of children and adults can drink a 16-ounce bottle of Pepsi, which has 55 grams of added sugar – roughly the amount in three medium apples – and no fiber. Fiber not only limits how much you can eat, but how quickly sugar leaves the intestine and reaches the liver, Dr. Stanhope said.

“You can’t easily eat that much sugar from fruit,” she said. “But nobody has any problem consuming a very high level of sugar from a beverage or from brownies and cookies.”

Why is it a problem to have too much sugar?

Many nutrition experts say that sugar in moderation is fine for most people. But in excess it can lead to metabolic problems beyond its effects on weight gain. The reason, studies suggest, is fructose. Any fructose you eat is sent straight to your liver, which specializes in turning it into droplets of fat called triglycerides.

“When you ingest fructose, almost all of it is metabolized by the liver, and the liver is very good at taking that fructose and converting it to fat,” said Dr. Mark Herman, an assistant professor of medicine at Harvard. Studies show a predictable response when people are asked to drink a sugary beverage: A rapid spike in the amount of triglycerides circulating in their bloodstreams. This also leads to a reduction in HDL cholesterol, the so-called good kind.

Over time, this combination – higher triglycerides and lower HDL – is one major reason sugar promotes heart disease, said Dr. Aseem Malhotra, a cardiologist and adviser to the United Kingdom’s national obesity forum. This sequence of events may even overshadow the effects of LDL cholesterol, the so-called bad kind.

“What many people don’t realize is that it’s triglycerides and HDL that are more predictive of cardiovascular disease than LDL cholesterol,” Dr. Malhotra said. “I’m not saying LDL isn’t important. But if there is a hierarchy, triglycerides and HDL are more important than LDL.”

Dr. Malhotra said that when people reduce their sugar intake, “their overall cholesterol profile improves.”

“I see this in so many of my patients,” he added. “The effects are rapid.”

How much sugar is too much?

One of the largest studies of added sugar consumption, which was led by the Centers for Disease Control and Prevention, found that adults who got more than 15 percent of their daily calories from added sugar had a higher risk of cardiovascular disease. For the average adult, that translates to about 300 calories, or 18 teaspoons of added sugar, daily. That may not sound like a lot. But considering that a single 12-ounce can of Coca-Cola has almost 10 teaspoons of sugar, it can add up quickly

The study found that most adults got more than 10 percent of their daily calories from added sugar, and that for 10 percent of people, more than 25 percent of their calories came from added sugar. The biggest sources for adults were soft drinks, fruit juices, desserts and candy.

While those might seem like obvious junk foods, Dr. Malhotra said, about half of the sugar Americans consume is “hidden” in less obvious places like salad dressings, bread, low-fat yogurt and ketchup. In fact, of the 600,000 food items for sale in America, about 80 percent contain added sugar.

Everyone’s tolerance for sugar is different. Studies show, for example, that people who are already obese may be more susceptible to metabolic harm from sugar than others. But Dr. Malhotra said that he generally advises people to follow the World Health Organization’s guidelines, which recommend that adults and children consume no more than about six teaspoons daily of added sugar.

“Could I tell you the exact limit where sugar starts to definitely impact cardiovascular health?” he said. “That’s difficult. But I think if people stick within the W.H.O. limits, then their risk is reduced.”

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Should You Take a Vitamin? Do You Know What a Vitamin Is?

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Credit Catherine Price

Many people can rattle off the names of the most popular vitamins and the foods that contain them in abundance. But understanding exactly what vitamins are and what roles they play in the body is far more complicated. In fact, though scientists recognize that there are 13 vitamins that are essential for good health, there is no real consensus on what they actually do and exactly how much of them we truly need.

Catherine Price, a science journalist, explores these questions and more in a book that was recently released in paperback, called “Vitamania: Our Obsessive Quest for Nutritional Perfection.” Ms. Price traces the history of vitamins from their discovery as lifesaving organic compounds that prevented strange diseases to their ubiquity today in foods, beverages and dietary supplements. Ms. Price sheds surprising light on the mythology surrounding vitamins and explains why even basic advice promoted by experts – like the nutrient requirements for healthy adults known as the recommended dietary allowance, or RDA – may be misguided.

Recently, we sat down with Ms. Price to discuss some of the most common misconceptions about vitamins, the reasons vitamin D testing can be misleading, and which questions you should ask yourself before deciding whether to take a multivitamin. Here are edited excerpts from our conversation.

Q.

Why did you write this book?

A.

I have Type 1 diabetes, which forces me to think about how food interacts with our bodies every time I eat. And yet when my husband turned to me out of the blue one day and asked, “What is a vitamin?” I realized I didn’t know the answer. Vitamins turned out to be a perfect subject for me. I love investigating things that seem so familiar to us that we never think to ask questions about them. They were a mystery hiding in plain sight, and I was intrigued.

Q.

How have vitamins changed the way we think about food?

A.

Vitamins were the first “superfoods”— they introduced the idea that there are particular foods, ingredients and dietary chemicals that have health benefits that go beyond mere nutrition. It turns out that there’s a direct line between the discovery and early marketing of vitamins and our current beliefs in the magical powers of kale. Learning about the history of vitamins made me much better at recognizing nutritional hype, which helps me make much better — and calmer — decisions about what to eat.

Q.

What are some of the most common misperceptions about vitamins?

A.

My biggest pet peeve is that when we hear the word “vitamin,” we automatically think of pills instead of food — and then use “vitamin” to refer to all dietary supplements. This is incorrect. There are only 13 vitamins, which are essential for health, compared to over 85,000 dietary supplements for sale in America. Also, we assume that scientists know exactly what vitamins do in our bodies and how much of each we need, but they don’t. We assume that all vitamins and dietary supplements are required to be tested for safety and effectiveness before they’re sold. But they’re not.

Q.

Should the average person take a multivitamin?

A.

Ask yourself what you eat. Does your plate look like the cover of a Michael Pollan book? Then you’re already getting plenty of vitamins and other nutrients from your food. Do you eat a lot of fortified foods like breakfast cereal and sports drinks? Then you probably don’t need to take a multivitamin either, because you’re essentially eating one. The people who benefit the most from multivitamins are those with restricted diets or health issues that make it hard to absorb nutrients from food, or who get most of their calories from foods that are so junky that they haven’t even been enriched with synthetic vitamins. Man cannot live on potato chips alone.

Q.

In your book you say it’s a bad idea to get tested for blood levels of vitamin D and other nutrients. Why?

A.

I wouldn’t say it’s necessarily bad — it’s more that it’s not particularly helpful. We know that vitamin D is essential for healthy bones, but the jury’s still out on what else it might do. This makes it impossible to determine what our requirements actually are, which in turn makes it impossible to figure out what an optimal level should be. And despite an ongoing standardization effort, results for the same blood sample can differ depending on which lab they’re sent to. It’s like taking an exam that doesn’t have an answer key — and that’s scored differently depending on who grades it.

Q.

Why is taking large doses of some vitamins a bad idea?

A.

It’s a bad idea to assume that just because something is essential in small doses, bigger doses must be better. Some vitamins are known to be toxic in high doses. Vitamin A is the most notorious. In some cases, high doses of vitamins that we thought would be helpful have been shown to cause more harm than good. In the 1990s, high doses of beta-carotene, which is a precursor to vitamin A, were tested as a possible prevention for cancer, but were eventually linked to an increased risk for lung cancer, especially among smokers. Remember: Even water can kill you if you drink too much of it.

Q.

In your book you argue that the “Percent Daily Value” figures on food and supplement labels are close to meaningless. Why?

A.

First of all, we each have different vitamin requirements, which means that 100 percent for me is not 100 percent for you. Second, the recommended dietary allowances aren’t meant as personalized recommendations to begin with. And third, most of the percentages in the “percent daily value” column on current food and supplement labels are calculated off of the RDAs from 1968. Yes, 1968. The FDA plans to use more updated recommendations in the next version of the nutrition and supplement facts panels, but for now, most of those numbers are still based on recommendations that are nearly a half a century old.

Q.

What are some of the most peculiar things you learned about vitamins while writing this book?

A.

That synthetic vitamin D is made by irradiating grease from sheep’s wool. That American politicians became convinced that thiamin deficiencies would make us lose World War II. That the guy who discovered vitamin B12 did so by eating raw meat, regurgitating it, and then tube-feeding it to his unknowing patients. And that before being affiliated with vitamins, Fred Flintstone and Barney Rubble used to advertise Winston cigarettes. It turns out that the story of vitamins is much bigger, weirder, more interesting and more useful than I ever could have anticipated.

Diet High in Saturated Fats May Be Linked to Dense Breasts

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Teenage girls who eat a diet high in saturated fat are at increased risk of developing dense breasts, a study concludes. Dense breasts contain more fibrous and connective tissue than normal and are a risk factor for breast cancer.

Researchers studied 177 girls, ages 10 to 18 at the start of the study, who periodically filled out dietary recall questionnaires. The scientists measured breast density by M.R.I. when the members of the group were 25 to 29 years old. The study is in Cancer Epidemiology, Biomarkers & Prevention.

Average dense breast volume in those in the lowest quarter for saturated fat intake was 16.4 percent, compared with 21.5 percent for those in the highest quarter.

Consumption of unsaturated fats had the opposite associations — the higher the consumption of unsaturated fats, the lower the average dense breast volume.

“We looked only at the associations of breast density with fat intake,” said the senior author, Joanne F. Dorgan, an epidemiologist at the University of Maryland School of Medicine. “Whether this will then be related to an increase in breast cancer later in life, we don’t know. But breast density itself is associated with increased risk.”

The authors controlled for many health factors, but they acknowledge that unknown variables could have affected their results.

“This is all observational data,” Dr. Dorgan said, “and needs to be confirmed before we can make health recommendations.”

The New Performance Enhancer in High School Sports? Nutrition

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Jordan Burg, 18, learned to make smart food choices for sports through a nutrition program at his school.

Jordan Burg, 18, learned to make smart food choices for sports through a nutrition program at his school.Credit Jenna Schoenefeld for The New York Times

Jordan Burg, 18, who plays varsity football and baseball and runs track, never used to think about what he was eating. But after he learned at school that nutrition was as important to his athletic performance as attending practice, he changed his diet.

Before, “I figured that I worked out so hard, it didn’t matter,” he said. “I ate ice cream whenever I pleased, cheese on everything and soda every day.” Now, he said, “I find myself at the salad bar having grilled chicken salads,” and on game days “I eat chicken breast and fish, and I make sure I drink as much water as possible.” He also avoids processed foods and red meat.

Jordan, a senior at the Windward School in Los Angeles, a private co-ed school for grades 7-12, said, “I am experiencing far fewer muscle cramps as well as less muscle fatigue.”

He credits this change to Windward’s heavy focus on nutrition as part of its athletic program, something that appears to be a new trend in high schools, said Molly Wong Vega, a dietitian who provides her services to three public school districts in the greater Houston area. Long a standard part of professional and college programs, the emphasis on diet is shifting to the high school level.

“Schools are starting to bring in dietitians to discuss the importance of nutrition with young athletes to complete the circle,” Ms. Wong Vega said. “Suggesting a snack of bell peppers with hummus may be a way to help increase vitamin A and C intake and give a little zinc as well,” which she says can help with muscle and tissue repair.

Ms. Wong Vega said public school districts often have tighter budgets than private schools, making it harder to hire specialists in sports nutrition. She is not employed directly by the schools but works with their athletic trainers through the Houston Methodist System, a network of hospitals. She said it took her and another dietitian a full semester to talk to all the coaching staff members and 900 athletes at just one high school.

The Chandler Unified School District in Arizona, a public district in the suburbs of Phoenix, has three dietitians on staff. One is Wesley Delbridge, also a spokesman for the Academy of Nutrition and Dietetics, a trade group representing some 75,000 registered dietitians and other nutrition professionals.

“By hiring a dietitian, districts receive that extra skill set that can improve their meals and increase health,” said Mr. Delbridge, a registered dietitian who directs the district’s food and nutrition department. “I have been advocating for school nutrition departments and food service departments to hire dietitians for some time, and I’m happy to see more and more schools incorporate nutrition not only into their athletic programs but into its core programs.”

Mr. Delbridge and his team developed “peak performance packs,” boxes of food that students in the district’s high schools can buy in the cafeteria for $5. There are three choices: endurance, muscle building and rapid recovery packs, each aimed at giving student athletes solid nutritional choices for their sport.

The endurance pack, for example — for sports like soccer, cross country, track and wrestling – contains whole-grain pasta salad, fresh fruit, string cheese, vegetables, hummus and a beverage high in electrolytes, intended to help prevent cramping and muscle fatigue. The muscle-building pack contains foods that are high in lean protein, both plant- and animal-based, to encourage muscles to repair and build up again.

Sports nutritionists concede that getting kids to eat healthfully remains a struggle.

“We don’t say ‘don’t eat this, don’t eat that,’” said Kermit Cannon, who heads the Windward School’s program to incorporate healthy eating into its curriculum. “We emphasize that good nutrition, along with sleep and exercise, will not only benefit you as a student athlete, but those habits will benefit you for a lifetime.”

Tackling eating disorders is also often part of the nutrition programs, with some dietitians providing one-on-one sessions with students. Mr. Delbridge is sometimes asked by a coach or a counselor to talk with student athletes who have eating disorders, and their parents.

“We would discuss their current weight, exercise activity and intensity, and I would show them what the final amount of calories they need in a day to maintain that activity level,” Mr. Delbridge said. “This can sometimes shock the student, because it seems like a lot of calories. Then we discuss how to meet these needs with healthy choices.”

Roberta Anding, a sports dietitian at the Kinkaid School, a private school in Houston for pre-kindergarten to 12th grade, said both boys and girls can struggle with body image. “How we provide these young men and women the life skills to navigate food choices, a college cafeteria, see how alcohol plays a negative role in your performance, how to recover properly — that’s truly focusing in on wellness for life.”

Robert Bach, the principal of Stillwater Area High School in Minnesota, said for several years now, students have had access to individual sessions with a nutritionist to help them make smart food choices. “It’s about lifelong health so that our students can lead a healthy lifestyle they carry beyond their classes,” he said.

Sela Kay, a sophomore at the Windward School, said that learning about nutrition at school has made it easier for her to make healthier food choices.

“Even after I am done with organized sports someday, I want to continue leading this healthy lifestyle,” said Sela, 16, who plays varsity basketball and runs track. “I know now that will start with my food choices.”

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How Well Do You Know Your Food Labels?

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New food products making claims about health and nutritional attributes are on the rise. With the average American grocery store carrying 42,214 items, it’s easy to see why a trip down the aisle can leave you scratching your head. Test your supermarket savvy with this quiz.

Sophie Egan is the author of “Devoured: From Chicken Wings to Kale Smoothies — How What We Eat Defines Who We Are,” on which this quiz is based.

A High-Fat Diet May Lead to Daytime Sleepiness

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Credit Tony Cenicola/The New York Times

Eating a high-fat diet may lead to daytime sleepiness, a new study concludes.

Australian researchers studied 1,800 men who had filled out food-frequency questionnaires and reported on how sleepy they felt during the day. They were also electronically monitored for obstructive sleep apnea, which causes people to wake up many times during the night.

After adjusting for factors that could influence sleep — smoking, alcohol intake, waist circumference, physical activity, medications, depression and others — they found that compared with those in the lowest one-quarter for fat intake, those in the highest one-quarter were 78 percent more likely to suffer daytime sleepiness and almost three times as likely to have sleep apnea.

The connection of fat intake to apnea was apparent most clearly in people with a high body mass index, but the positive association of fat intake with daytime sleepiness persisted strongly in all subjects, regardless of B.M.I. Thestudy is in the journal Nutrients.

“The possible mechanism could be meal timing, but we didn’t have that information,” said the lead author, Yingting Cao, a doctoral candidate at the University of Adelaide. “But we have reason to believe that circadian rhythm, hormones and diet all work together to create these effects.

“Everyone knows that diet has an important effect on health,” she continued. “Extremely high fat intake is not good for sleep. So the key message here is to eat healthy. But that’s easier to say than to do.”

Dr. Thomas Farley Takes on Big Food and Big Tobacco

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Credit Dan Deitch

A century ago, most local health departments concentrated their efforts on fighting infectious diseases like cholera, polio and tuberculosis. But today, many health departments have a very different focus: cancer, heart disease and Type 2 diabetes, some of America’s leading killers. Fighting these diseases often means promoting changes in lifestyle and behavior, and no health department has done that more aggressively than New York City’s.

Under former Mayor Michael R. Bloomberg, New York’s health commissioners — first Dr. Thomas R. Frieden, and then Dr. Thomas A. Farley — took on smoking, sugary drinks, sodium, trans fats and binge drinking. Those battles weren’t always successful. A state court struck down the city’s controversial soda tax initiative, and critics complained that New York City was becoming a “nanny” state.

But Dr. Farley, who served as New York’s health commissioner from 2009 to 2014, says the city’s efforts helped demonstrate that the key to eradicating lifestyle-related diseases is by changing environments — making bad choices harder and good ones easier. He makes a case for this approach in his latest book, “Saving Gotham: Billionaire Mayor, Activist Doctors, and the Fight for Eight Million Lives,” which shares the behind-the-scenes story of the Bloomberg administration’s radical approach to fighting chronic disease.

Dr. Farley, who later served as the Joan H. Tisch Distinguished Fellow in Public Health at Hunter College and chief executive of the Public Good Projects, is now the health commissioner of Philadelphia, where earlier this month the mayor proposed a soda tax as a way to fund schools, libraries, and parks and recreation centers. Recently we caught up with Dr. Farley to talk about his book, his battles with the beverage industry and how his approach to public health may have influenced other health departments around the world. Here are edited excerpts from our conversation.

Q.

Why did you write your latest book, “Saving Gotham”?

A.

I wanted to show that there’s a way to fight disease other than through expensive medical care. In the United States, we spend roughly twice as much per capita for medical care as other high-income countries, and our health statistics are close to last. People naturally assume we’re going to solve this problem through medical care. But it doesn’t fit with those statistics. There’s a different approach — a public health approach — that costs very little. The book tells the story of how with using that public health approach we were able to prevent the leading causes of death and save many lives.

Q.

As New York City’s health commissioner you led many public health campaigns. Which had the most impact?

A.

I would say it was our efforts to reduce smoking. During the time of the Bloomberg administration, smoking rates fell by about 25 percent in New York. Since then they’ve fallen by about a third. That’s about 400,000 fewer smokers. And that alone should save thousands if not tens of thousands of lives. At the same time, sugary drink consumption fell by about a third, and heart disease mortality fell by about 40 percent.

Q.

Did these efforts ultimately translate into an increase in life expectancy?

A.

Absolutely. During the Bloomberg years, life expectancy at birth in New York City increased by about 3.2 years. During the same period, life expectancy in the U.S. as a whole increased by 1.8 years. So we were fast outpacing the rest of the country, and that increase in life expectancy was bigger than it was in any other big city in America.

Q.

Some of your health initiatives created a lot of controversy. Where did you find the most resistance?

A.

There was controversy, but most of the resistance came from industry. In the book, I show how some of the biggest risks today are coming from companies that make, sell and market products that over a lifetime make us sick, like cigarettes and sugary drinks.

When New York City passed the smoke-free air rule that made bars and restaurants smoke free, it was a radical idea. And that idea has now spread across most of the U.S. and almost all of Europe — so much so that it’s almost hard to imagine what it would be like to have smoking in a bar or restaurant. The book shows how those good ideas can quickly spread from one city to others, despite resistance from industry.

Q.

The beverage industry says that sugary drink taxes disproportionately hurt the poor economically. How do you respond?

A.

I would say that the poor are disproportionately suffering from obesity and Type 2 diabetes as a consequence of sugary drinks. They drink more sugary drinks now than people who have more money. Because people with lower incomes are more price-sensitive, they will disproportionately benefit from efforts to reduce sugary drink consumption.

Q.

The new soda tax proposal in Philadelphia was presented as a way to generate more revenue for the city, rather than as a “sin tax.” Do you think that will make it more appealing to the public?

A.

This is something that is central to the mayor’s agenda, and I think his way of approaching it is terrific. The revenue from the sugary drink tax will go for pre-K, for what they call community schools — which is providing services for children so they can stay in school and learn — and for rebuilding the city’s parks and recreation centers. All of those preferentially benefit people of lower income in Philadelphia. All of those are very popular and will benefit health over the long term. It’s a great way to match up the benefits of the tax revenue with a source of revenue that is also good for health.

Q.

You have spent a lot of time fighting the beverage industry. Have you seen any change in their response over the years?

A.

The beverage companies understand that they’re going to have to change the way that they do business. And they are making changes — but they’re not making changes fast enough. They still market very heavily these products that are major contributors to our health problems. In the end, they will move only as fast as we push them.

Q.

How did New York’s health initiatives impact the greater public health landscape?

A.

That was another theme I tried to bring out in the book. This is the story of a local health department reinventing itself to take on the biggest health problems of our time. Before the Bloomberg period, most local health departments were seen as organizations that did restaurant inspections and rat control. We showed that local health departments could take on smoking and make a meaningful difference in life expectancy. That model is now being copied by local health departments around the country. And that’s why I think local health departments are where you’re seeing public health innovation right now.

Q.

Are there any common misconceptions about the role of public health agencies that you have tried to dispel?

A.

A thing that people often don’t understand and that I hoped to show in the book is that health is political, but not in the way that most people think. If you ask most reporters about the politics of health, they’re going to talk about Obamacare. But as you saw in the book, the fights we faced over health were with the tobacco industry and with the food industry. I hope people read the book just for the story, because it’s a great story, but that in the end they will have learned the great value of public health.

A Decades-Old Study, Rediscovered, Challenges Advice on Saturated Fat

A four-decades-old study — recently discovered in a dusty basement — has raised new questions about longstanding dietary advice and the perils of saturated fat in the American diet.

The research, known as the Minnesota Coronary Experiment, was a major controlled clinical trial conducted from 1968 to 1973, which studied the diets of more than 9,000 people at state mental hospitals and a nursing home.

During the study, which was paid for by the National Heart, Lung and Blood Institute and led by Dr. Ivan Frantz Jr. of the University of Minnesota Medical School, researchers were able to tightly regulate the diets of the institutionalized study subjects. Half of those subjects were fed meals rich in saturated fats from milk, cheese and beef. The remaining group ate a diet in which much of the saturated fat was removed and replaced with corn oil, an unsaturated fat that is common in many processed foods today. The study was intended to show that removing saturated fat from people’s diets and replacing it with polyunsaturated fat from vegetable oils would protect them against heart disease and lower their mortality.

So what was the result? Despite being one of the largest controlled clinical dietary trials of its kind ever conducted, the data were never fully analyzed.

Several years ago, Christopher E. Ramsden, a medical investigator at the National Institutes of Health, learned about the long-overlooked study. Intrigued, he contacted the University of Minnesota in hopes of reviewing the unpublished data. Dr. Frantz, who died in 2009, had been a prominent scientist at the university, where he studied the link between saturated fat and heart disease. One of his closest colleagues was Ancel Keys, an influential scientist whose research in the 1950s helped establish saturated fat as public health enemy No. 1, prompting the federal government to recommend low-fat diets to the entire nation.

“My father definitely believed in reducing saturated fats, and I grew up that way,” said Dr. Robert Frantz, the lead researcher’s son and a cardiologist at the Mayo Clinic. “We followed a relatively low-fat diet at home, and on Sundays or special occasions, we’d have bacon and eggs.”

The younger Dr. Frantz made three trips to the family home, finally discovering the dusty box marked “Minnesota Coronary Survey,” in his father’s basement. He turned it over to Dr. Ramsden for analysis.

The results were a surprise. Participants who ate a diet low in saturated fat and enriched with corn oil reduced their cholesterol by an average of 14 percent, compared with a change of just 1 percent in the control group. But the low-saturated fat diet did not reduce mortality. In fact, the study found that the greater the drop in cholesterol, the higher the risk of death during the trial.

The findings run counter to conventional dietary recommendations that advise a diet low in saturated fat to decrease heart risk. Current dietary guidelines call for Americans to replace saturated fat, which tends to raise cholesterol, with vegetable oils and other polyunsaturated fats, which lower cholesterol.

While it is unclear why the trial data had not previously been fully analyzed, one possibility is that Dr. Frantz and his colleagues faced resistance from medical journals at a time when questioning the link between saturated fat and disease was deeply unpopular.

“It could be that they tried to publish all of their results but had a hard time getting them published,” said Daisy Zamora, an author of the new study and a research scientist at the University of North Carolina at Chapel Hill.

The younger Dr. Frantz said his father was probably startled by what seemed to be no benefit in replacing saturated fat with vegetable oil.

“When it turned out that it didn’t reduce risk, it was quite puzzling,” he said. “And since it was effective in lowering cholesterol, it was weird.”

The new analysis, published on Tuesday in the journal BMJ, elicited a sharp response from top nutrition experts, who said the study was flawed. Walter Willett, the chairman of the nutrition department at the Harvard T.H. Chan School of Public Health, called the research “irrelevant to current dietary recommendations” that emphasize replacing saturated fat with polyunsaturated fat.

Frank Hu, a nutrition expert who served on the government’s 2015 dietary guidelines committee, said the Minnesota trial was not long enough to show the cardiovascular benefits of consuming vegetable oil because the patients on average were followed for only about 15 months. He pointed to a major 2010 meta-analysis that found that people had fewer heart attacks when they increased their intake of vegetable oils and other polyunsaturated fats over at least four years.

“I don’t think the authors’ strong conclusions are supported by the data,” he said.

To investigate whether the new findings were a fluke, Dr. Zamora and her colleagues analyzed four similar, rigorous trials that tested the effects of replacing saturated fat with vegetable oils rich in linoleic acid. Those, too, failed to show any reduction in mortality from heart disease.

“One would expect that the more you lowered cholesterol, the better the outcome,” Dr. Ramsden said. “But in this case the opposite association was found. The greater degree of cholesterol-lowering was associated with a higher, rather than a lower, risk of death.”

One explanation for the surprise finding may be omega-6 fatty acids, which are found in high levels in corn, soybean, cottonseed and sunflower oils. While leading nutrition experts point to ample evidence that cooking with these vegetable oils instead of butter improves cholesterol and prevents heart disease, others argue that high levels of omega-6 can simultaneously promote inflammation. This inflammation could outweigh the benefits of cholesterol reduction, they say.

In 2013, Dr. Ramsden and his colleagues published a controversial paper about a large clinical trial that had been carried out in Australia in the 1960s but had never been fully analyzed. The trial found that men who replaced saturated fat with omega-6-rich polyunsaturated fats lowered their cholesterol. But they were also more likely to die from a heart attack than a control group of men who ate more saturated fat.

Ron Krauss, the former chairman of the American Heart Association’s dietary guidelines committee, said the new research was intriguing. But he said there was a vast body of research supporting polyunsaturated fats for heart health, and that the relationship between cholesterol-lowering and mortality could be deceiving.

People who have high LDL cholesterol, the so-called bad kind, typically experience greater drops in cholesterol in response to dietary changes than people with lower LDL. Perhaps people in the new study who had the greatest drop in cholesterol also had higher mortality rates because they had more underlying disease.

“It’s possible that the greater cholesterol response was in people who had more vascular risk related to their higher cholesterol levels,” he said.

Dr. Ramsden stressed that the findings by he and his colleagues should be interpreted cautiously. The research does not show that saturated fats are beneficial, he said: “But maybe they’re not as bad as people thought.”

The research underscores that the science behind dietary fat may be more complex than nutrition recommendations suggest. The body requires omega-6 fats like linoleic acid in small amounts. But emerging research suggests that in excess linoleic acid may play a role in a variety of disorders including liver disease and chronic pain.

A century ago, it was common for Americans to get about 2 percent of their daily calories from linoleic acid. Today, Americans on average consume more than triple that amount, much of it from processed foods like lunch meats, salad dressings, desserts, pizza, french fries and packaged snacks like potato chips. More natural sources of fat such as olive oil, butter and egg yolks contain linoleic acid as well but in smaller quantities.

Eating whole, unprocessed foods and plants may be one way to get all the linoleic acid your body needs, Dr. Ramsden said.

Fruits and Vegetables to Fight Cataracts

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Credit Andrew Scrivani for The New York Times

Here’s another reason to eat your fruits and veggies: You may reduce your risk of vision loss from cataracts.

Cataracts that cloud the lenses of the eye develop naturally with age, but a new study is one of the first to suggest that diet may play a greater role than genetics in their progression.

Researchers had about 1,000 pairs of female twins in Britain fill out detailed food questionnaires that tracked their nutrient intake. Their mean age was just over 60.

The study participants underwent digital imaging of the eye to measure the progression of cataracts. The researchers found that women who consumed diets rich in vitamin C and who ate about two servings of fruit and two servings of vegetables a day had a 20 percent lower risk of cataracts than those who ate a less nutrient-rich diet.

Ten years later, the scientists followed up with 324 of the twin pairs, and found that those who had reported consuming more vitamin C in their diet — at least twice the recommended dietary allowance of 75 milligrams a day for women (the R.D.A. for adult men is 90 milligrams) — had a 33 percent lower risk of their cataracts progressing than those who get less vitamin C.

The researchers concluded that genetic factors account for about 35 percent of the difference in cataract progression, while environmental factors like diet account for 65 percent.

“We found no beneficial effect from supplements, only from the vitamin C in the diet,” said Dr. Christopher Hammond, a professor of ophthalmology at King’s College London and an author of the study,published in Ophthalmology. Foods high in vitamin C include oranges, cantaloupe, kiwi, broccoli and dark leafy greens.

”This probably means that it is not just vitamin C but everything about a healthy diet that is good for us and good for aging,” he added.

Few Americans Follow 4 Main Pillars of Heart Health

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Most Americans know that a heart-healthy lifestyle includes eating a healthful diet, not smoking, being physically active and keeping weight and body fat down. But a new study found that fewer than 3 percent of American adults could claim all four healthy elements.

Only 2.7 percent of the Americans in the study were nonsmokers who ate a reasonably good diet, including eating plenty of vegetables and whole grains and avoiding saturated fat; got at least 150 minutes of moderate exercise a week; and had a healthy percentage of body fat, defined as up to 20 percent for men and 30 percent for women.

The results were “shocking,” said Ellen Smit, an associate professor at Oregon State University College of Public Health and Human Sciences and the senior author of the report. “I think it’s a wake-up call.”

The study, published in Mayo Clinic Proceedings, was based on data gathered from the National Health and Nutrition Examination Survey from 2003 to 2006 and included a nationally representative sample of 4,745 Americans.

Eating habits were self-reported, which can be unreliable, but other measures were based on objective tests, including blood samples to verify smoking status, a sophisticated X-ray test to determine body fat, and accelerometers to measure physical activity.

 

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Intermittent Fasting Diets Are Gaining Acceptance

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Credit Gary Taxali

Mark Mattson, a neuroscientist at the National Institute on Aging in Maryland, has not had breakfast in 35 years. Most days he practices a form of fasting — skipping lunch, taking a midafternoon run, and then eating all of his daily calories (about 2,000) in a six-hour window starting in the afternoon.

“Once you get used to it, it’s not a big deal,” said Dr. Mattson, chief of the institute’s laboratory of neurosciences. “I’m not hungry at all in the morning, and this is other people’s experience as well. It’s just a matter of getting adapted to it.”

In a culture in which it’s customary to eat three large meals a day while snacking from morning to midnight, the idea of regularly skipping meals may sound extreme. But in recent years intermittent fasting has been gaining popular attention and scientific endorsement.

It has been promoted in best-selling books and endorsed by celebrities like the actors Hugh Jackman and Benedict Cumberbatch. The late-night talk show host Jimmy Kimmel claims that for the past two years he has followed an intermittent fasting program known as the 5:2 diet, which entails normal eating for five days and fasting for two — a practice Mr. Kimmel credits for his significant weight loss.

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Credit Gary Taxali

Fasting to improve health dates back thousands of years, with Hippocrates and Plato among its earliest proponents. Dr. Mattson argues that humans are well suited for it: For much of human history, sporadic access to food was likely the norm, especially for hunter-gatherers. As a result, we’ve evolved with livers and muscles that store quickly accessible carbohydrates in the form of glycogen, and our fat tissue holds long-lasting energy reserves that can sustain the body for weeks when food is not available.

“From an evolutionary perspective, it’s pretty clear that our ancestors did not eat three meals a day plus snacks,” Dr. Mattson said.

Across the world, millions of people fast periodically for religious and spiritual reasons. But some are now looking at the practice as a source of health and longevity.

Valter Longo, the director of the Longevity Institute at the University of Southern California, initially studied fasting in mice that showed that two to five days of fasting each month reduced biomarkers for diabetes, cancer and heart disease. The research has since been expanded to people, and scientists saw a similar reduction in disease risk factors.

Dr. Longo said the health benefits of fasting might result from the fact that fasting lowers insulin and another hormone called insulinlike growth factor, or IGF-1, which is linked to cancer and diabetes. Lowering these hormones may slow cell growth and development, which in turn helps slow the aging process and reduces risk factors for disease.

“When you have low insulin and low IGF-1, the body goes into a state of maintenance, a state of standby,” Dr. Longo said. “There is not a lot of push for cells to grow, and in general the cells enter a protected mode.”

Critics say that health benefits or not, various forms of intermittent fasting are too impractical for most people.

The 5:2 diet, for example, advocates eating without restrictions for five days and then consuming just 500 calories — roughly the equivalent of a light meal — on each of the other two days of the week. Another regimen, called alternate-day fasting, involves eating no more than 500 calories every other day.

A third regimen, which Dr. Mattson follows, is known as time-restricted feeding. The idea is to consume all of the day’s calories in a narrow window, typically six to eight hours, and fasting for the remaining 16 to 18 hours in a day. Studies of time-restricted feeding practices in both animals and humans have suggested that the practice may lower cancer risk and help people maintain their weight.

The scientific community remains divided about the value of intermittent fasting. Critics say that the science is not yet strong enough to justify widespread recommendations for fasting as a way to lose weight or boost health, and that most of the evidence supporting it comes from animal research. Advocates say the body of research on intermittent fasting is growing rapidly and indicates that the health benefits are striking.

The 5:2 diet, in particular, is backed by “promising” studies that show that it lowers weight and improves blood sugar, inflammation and other aspects of metabolic health, said Joy Dubost, a registered dietitian and a spokeswoman for the Academy of Nutrition and Dietetics, the country’s largest organization of dietitians. She noted that fasting isn’t appropriate for pregnant women, people with diabetes and people on medications.

“Most people who do this understand that it’s not about binge eating,” Dr. Dubost said. “But they like that it gives them the freedom not to worry about calories, carbs and other restrictions on days when they’re not fasting.”

Krista Varady, an associate professor of nutrition at the University of Illinois at Chicago, has studied the effects of alternate-day fasting on hundreds of obese adults. In trials lasting eight to 10 weeks, she has found that people lose on average about 13 pounds and experience marked reductions in LDL cholesterol, blood pressure, triglycerides and insulin, the fat-storage hormone.

Dr. Varady found in her research that intermittent fasting was easiest when people ate a moderately high-fat diet and were allowed to consume up to 500 calories on their fasting days. In her studies, 10 percent to 20 percent of people usually find the diet too difficult and quickly stop. Those who stick with it typically adjust after a rocky first few weeks.

“We’ve run close to 700 people through various trials,” Dr. Varady said. “We thought people would overeat on their feast days to compensate. But people for some reason, regardless of their body weight, can only eat about 10 or 15 percent more than usual. They don’t really overeat, and I think that’s why this works.”

In 2011, Dr. Mattson and his colleagues reported a study of the 5:2 program that followed 107 overweight and obese women. Half of the subjects were assigned to eat no more than 500 calories each on two consecutive days each week. A control group was assigned to follow a low-calorie diet.

After six months, both groups had lost weight. But the intermittent fasting group lost slightly more — about 14 pounds on average — and had greater reductions in belly fat. They also retained more muscle and had greater improvements in blood sugar regulation.

Dr. Mattson’s interest in intermittent fasting grew out of work on animals that showed that alternate-day fasting protected mice from strokes, Alzheimer’s and Parkinson’s disease, and consistently extended their life spans by 30 percent. Dr. Mattson and his colleagues found that alternate-day fasting increased the production of proteins that protect brain cells, enhancing their ability to repair damaged DNA. Fasting, he said, acts as a mild stress that makes cells throughout the body stronger, shoring up their ability to adapt to later insults.

In this way, intermittent fasting is like exercise, which causes immediate stress and inflammation, but protects against chronic disease in the long run. Eating fruits and vegetables may have a similar effect. While very large doses of antioxidants can cause cancer in humans, moderate amounts of exposure can make cells more resilient, Dr. Mattson said.

“There is overlap between the way cells respond to exercise, to fasting, and even to exposure to some of the chemicals in fruits and vegetables,” he added.

Dr. Mattson is now starting a rigorous clinical trial of people 55 to 70 years old who are prediabetic and at high risk for developing Alzheimer’s disease. He plans to study whether intermittent fasting may slow cognitive decline.

Dr. David Ludwig, a professor of nutrition at the Harvard T. H. Chan School of Public Health, said one benefit of fasting is that it forces the body to shift from using glucose for fuel to using fat. During this process, the fat is converted to compounds known as ketones, a “clean” energy source that burns more efficiently than glucose, like high-octane gasoline, Dr. Ludwig said.

The same process, known as ketosis, occurs when people go on extremely low-carb, high-fat diets. Dr. Ludwig said ketones seem to have unique effects on the brain. High-fat diets, for example, have been used for years to treat people who suffer from epileptic seizures.

“There are extensive reports of children who had debilitating seizures who were cured on ketogenic diets,” Dr. Ludwig said. “If it benefits the brain to prevent seizures, then maybe it benefits the brain in other ways.”

Dr. Ludwig noted that the long-term effectiveness of fasting had not been well studied. He cautioned that for many people, fasting is simply too difficult and may slow metabolism. A potentially more practical approach is to limit sugar and other processed carbohydrates, replacing them with natural fats, protein and unrefined carbohydrates, he said.

“It takes a very disciplined person to skip a couple meals every day,” he added.

But Dr. Mattson, who has been skipping meals for decades, said the adjustment to skipping breakfast and lunch was a lot like the change that occurs when a couch potato starts exercising.

“If you’ve been sedentary for years and then you go out and try to run five miles, you’re not going to feel very good until you get in shape,” he said. “ It’s not going to be a smooth transition right away. It takes two weeks to a month to adapt.”

Have You Tried a Fasting Diet? Tell Us About It.

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