Understanding How Breastfeeding Affects Obesity

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Recent studies questioned whether breastfeeding can lower rates of obesity among kids, and the latest analysis will only add to the confusion.

Researchers from Okayama University in Japan reported that among 43,300 Japanese children, those who were only breastfeed at six to seven months were less likely to be overweight or obese at ages seven or eight compared to kids who drank formula.

That’s reassuring for advocates of breastfeeding, who have always maintained that the practice has health benefits for both mom and baby that include helping both to keep up healthy weights. But a study published in the Journal of the American Medical Association in March undermined the association by noting that in a population of babies born in Belarus breastfed babies experienced fewer health issues but were not slimmer than formula fed babies. “There’s a lot of other evidence out there to continue to support breast-feeding, but in terms of breastfeeding reducing obesity, it’s unlikely to be effective,” the study’s lead author, Dr. Richard Martin, a professor of clinical epidemiology at the University of Bristol in the U.K. told TIME.

Currently, the World Health Organization and the American Academy of Pediatrics recommend that mothers breastfeed babies exclusively for at least six months in order to avoid diarrheal and infectious diseases and to provide the energy that newborns need in their first few months of life. Both also cite the lower risk of childhood obesity as a reason for supporting breastfeeding and rely on several studies to support their position. In 2011, a paper published in the journal JAMA Pediatrics encouraged mothers to breastfeed in order to combat weight gain among their kids. The researchers wrote that early introduction of solids like cereal or dried baby food was linked to a greater risk of both obesity and food allergies: “Breast milk provides your baby with food that is easy to digest and very nutritious, and your child helps decide how much to eat and when to eat it. Both the breast milk itself and the way your baby feeds help him or her to develop healthy eating patterns. Breastfed babies seem to be better able to regulate their food intake and thus are at lower risk for obesity.”

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Even mothers can benefit from healthier weights while breastfeeding. A 2010 study from University of Pittsburgh suggested that breastfeeding helps moms lose the abdominal fat they gain while pregnant, which is good for nourishing the developing baby, but not so healthy for moms after birth. In TIME’s report on the study, lead investigator Dr. Eleanor Bimla Schwarz at University of Pittsburgh said, “When women don’t breastfeed after pregnancy, or lactation is curtailed or prematurely discontinued, women end up retaining more fat than they would have if they breastfed. Then the mother’s health can suffer.”

Other studies have found breastfed infants have lower rates of type 2 diabetes, higher IQs and even higher social status as adults than their formula-fed counterparts.

The AAP stands by the evidence that breastfeeding can protect against obesity, noting that differences in the way the current study and the earlier one questioning breastfeeding’s influence on weight could explain the conflicting results. “Many of the studies have just looked at any breastfeeding vs. formula feeding and those are the kinds of studies where the evidence is the least strong. It’s really the studies that look at exclusive breastfeeding for about six months that provide the strongest evidence for the link between breastfeeding and obesity protection,” says Dr. Lori Feldman-Winter, a spokesperson for the AAP and division head of adolescent medicine at Cooper University Hospital.

(MOREIs the Medical Community Failing Breastfeeding Moms?)

And Feldman-Winter says it may be that both breastfeeding — with the baby attached to mom’s breast — and the breast milk that may be important in influencing babies’ weight. In suckling, it’s the baby that dictates how much he drinks, whereas with bottle-feeding, whether it’s breast milk or formula, it’s mom that tends to determine when baby has had enough. “A baby who is breastfeeding at the breast will suckle, and some of that time will be spent in nutritive suckling and some of that time in getting nourishment, but a lot of the time babies are suckling at the breast in a non-nutritive way and really self regulating the amount of calories they take in,” she says.

So as confusing as the conflicting studies may seem, Feldman-Winter says the bulk of data still support exclusive breastfeeding for at least the first six months as a healthy way to feed newborns and keep them at healthy weights when they grow older. That’s not always easy, however, and the debate over breastfeeding continues to ignite controversy in political and social, as well as medical communities. When Newark Mayor Corey Booker recently partnered with Nestle Corporation to tackle childhood obesity, breastfeeding advocates were outraged, since the company manufactures Gerber infant formula, and lactation advocates were concerned the city would start to push formula over breastfeeding. Hospitals regularly ignite controversy by sending mothers home with new baby kits that contain formula-based literature or, in the case of about half of New York City hospitals, educating them about the “Latch on NYC” breastfeeding initiative, in which mothers are only provided formula if medically necessary for their babies.

Such extreme measures may not help new moms to make a decision about breastfeeding; what these mothers need is a more comprehensive post-natal experience that educates them about what they need to know to care for their newborn, including how to either breast or formula feed, and provides them with the freedom to make the decision that’s right for their lifestyles.