The Perfect Waistline, in the Not-So-Perfect Past

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Most people wouldn’t look to their college days for insights into improving their health. But maybe there is something those of us in middle age can learn from our 20-year-old selves.

What did you weigh at age 20? As it turns out, that’s when your body probably settled into its ideal weight. By 20, almost everyone has stopped growing, and the pounds gained in the years following are mostly fat, says Dr. Walter Willett, a nutritional epidemiologist at Harvard University.

For most of us, what you weighed at age 20 is a far better gauge for judging your ideal weight than the standard weight and body mass index charts. Most of those tables cover such a wide range of weights that they can be misleading. According to many of them, the perfect weight for a woman who is 5-foot-7 could range anywhere from 118 to 159 pounds.

But what if that same woman weighs 159 pounds today, at age 40, but weighed 120 pounds in her early 20’s? That means her body has packed on 39 pounds — a gain of more than 30 percent, or about two pounds a year. The charts may say she’s healthy, but studies show that even a modest weight gain in adulthood is associated with a higher mortality risk.

In one Harvard analysis, women who gained eight to 22 pounds had a 15 percent higher risk of dying during the 24-year study period. Excess fat predicts many health problems, according to Dr. Willett, including heart disease, diabetes, many cancers, arthritis and even cataracts. Ideally, he adds, none of us should gain more than five pounds after the age of 20.

Obviously people who had serious weight problems or eating disorders in their 20’s, or someone who has bulked up from muscle building, can’t use their weight at 20 for predicting their ideal weight. And unfortunately, the weight-at-20 rule may not apply when the next generation reaches middle age. “An increasing part of the population is arriving at age 20 already overweight,” said Dr. Willett. “But even for these people, the first goal is to not gain more weight.”