By the time my third child was born, I was in pediatric practice, advising new mothers about the American Academy of Pediatrics guidelines: exclusive breast-feeding for the baby’s first six months. Then, as foods are introduced, continuing breast-feeding until at least the first birthday.

I had not managed either with my first two children, one born while I was in medical school, the second right at the end of my residency. I had breast-fed them both, but relied on formula to get through day care days, and the breast-feeding had ended altogether by seven or eight months.

But with my third, since I was a full-fledged practicing pediatrician, I felt a moral obligation to follow the recommendations that I had been earnestly dispensing. So I borrowed an electric breast pump and got serious.

Like most pediatricians, I am a true believer in the benefits of breast-feeding, though I myself was bottle-fed, along with many in my cohort (what can I say, I was born in the 1950s). But my own decision was mostly about that feeling that I had to un-hypocrite myself.

Dr. Michael Kramer, a professor of pediatrics and epidemiology at McGill University Faculty of Medicine, who was the lead author of a 2012 review of research on the optimal duration of exclusive breast-feeding, said that the case for exclusivity and longer duration starts with the realization that, “some breast-feeding benefits are realized only during the time of breast-feeding.” These include protection against infections and a lower risk of sudden infant death syndrome, and the effects are stronger when the breast-feeding is exclusive.

In poorer countries, Dr. Kramer said, breast-feeding children beyond 6 months leads to lower mortality rates. “For parents in a developed country, one of the main motivators is neurocognitive development, accelerated brain development,” he said.

“We really don’t know what it is about breast-feeding, whether it’s something in the milk, whether it has to do with increased physical contact between lactating mother and nursing baby, or if just the time it takes to breast-feed means increased opportunities for verbal exchange between mother and baby,” Dr. Kramer said. “I think that is an interesting topic for future research.”

Dr. Kramer was the lead researcher on the Promotion of Breast-feeding Intervention Trial (Probit), which studied 17,000 mother-infant pairs in Belarus starting in the mid-90s and demonstrated these neurocognitive effects. Half of the mothers, who had all begun breast-feeding at birth, received additional support and encouragement to keep breast-feeding.

In many past studies, it was hard to know whether some of the differences between breast-fed and bottle-fed infants could be attributed to other factors that affected who chose to breast-feed and who didn’t. The Probit experimental design let researchers measure the effects of longer and more exclusive exposure to breast milk, and the results have helped shape recommendations from the World Health Organization and American Academy of Pediatrics.

Dr. Maryam Sattari, an associate professor of medicine at the University of Florida, was the lead author of a 2016 study on the breast-feeding intentions and practices of 72 internal medicine physicians. The study found that 78 percent of the babies were exclusively breast-fed at birth and 40 percent of them at 12 months, though 63 percent of the mothers had planned to go to a year. “These are moms who are highly educated, highly motivated, they all want to do it,” Dr. Sattari said.

What helped these mothers, she said, was encouragement from medical leadership, as well as appropriate space and time to pump.

The internists did better than the general population in the Centers for Disease Control and Prevention’s breast-feeding report card on women in the United States breast-feeding babies born in 2013. While breast-feeding overall is on the rise, the numbers show that many mothers in this country are not following the A.A.P. recommendations. Compared to 2003, more women in 2013 were initiating breast-feeding (81 percent, up from 73 percent), and still breast-feeding at a year (31 percent, up from 20 percent).

Cria Perrine, an epidemiologist in the C.D.C.’s Division of Nutrition, Physical Activity and Obesity, said that those numbers don’t show some of the differences between demographic groups; breast-feeding rates are lower among African-Americans, and among less educated women and low-income women. Our culture needs to do a better job of supporting women who breast-feed, she said.

It’s also really important not to make someone who can’t or doesn’t — like my own mother — feel like a bad parent. And it would be terrible to make someone who breast-feeds as long as she can feel that she has in some sense failed. We should be cheering mothers on, and acknowledging their choices.

Dr. Julie Lumeng, a professor of pediatrics at the University of Michigan, had her first child as a pediatric resident. She recalls that it was difficult to find the time that she needed for pumping, and that she knew that just mentioning it made some of her colleagues uncomfortable, even in pediatrics. Still, she was deeply aware of the pediatric recommendation and the need to live up to it. “I would have stopped a lot earlier, but it was just not socially acceptable as a pediatrician among my peers to not be breast-feeding,” she said.

With my own third child, I made it to six months exclusively, me and my trusty electric breast pump. At times I felt I had gone a little off the deep end in my intense curation of those bags of frozen breast milk, carefully ferried to the day care center every day. It was a great relief when my son began avidly eating other foods, and it was then easier to go on breast-feeding him, evenings and weekends and whenever it made sense. We kept going till he was a little over a year old.

The experience made me deeply aware of how much this advice I give is asking of women, and how hard it would have been to do this if my own life were less privileged and less well supported.