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Breastfed Children Less Likely to Become Obese

New research from Ireland finds 9-year-olds are far less likely to be obese if their mothers breastfed them for at least six months.
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The Walt Disney Company’s announcement that its child-oriented television channels and websites will reject ads for unhealthy foods has been widely welcomed. But a new study from Ireland suggests there’s something mothers can do long before their kids reach cartoon-watching age to decrease the kids' odds of becoming obese.

Breastfeed them. And do so for at least six months.

This recommendation isn’t radically new: A 2004 review of nine studies concluded that breastfeeding “reduced the risk of obesity in childhood significantly.” But the Irish study, recently published in the journal Social Science and Medicine, provides what is arguably the strongest evidence yet of its effectiveness.

Using a large and representative sample of 8,568 Irish children—one-seventh of all the kids born in that nation between 1997 and 1998—it finds extended breast feeding can cut the risk of childhood obesity in half.

“Breastfeeding for between 13 and 25 weeks was associated with a 38 percent reduction in the risk of obesity at 9 years of age,” report Cathal McCrory and Richard Layte of Dublin’s Economic and Social Research Institute. “Being breastfed in excess of 26 weeks was associated with a 51 percent reduction in risk of obesity.”

The researchers designed their study to address a criticism of past research on this topic: Previous studies often failed to take into account the weight of a child’s parents. They note that the parents’ BMI (Body-Mass Index) is “amongst the strongest determinants” of children being overweight.

Using the aforementioned large sample of 9-year-olds, McCrory and Layte compared their height and weight with their parents’ memories of whether and how long they were breastfed. They factored in other conditions associated with childhood obesity, including low socioeconomic status and a lack of physical activity.

Taking all that into account, they found a strong link between breastfeeding and obesity, so long as the mother didn’t stop after just a few months. The benefits of breastfeeding didn’t show up statistically unless it continued for at least 13 weeks, and increased significantly for those children breastfed for 26 weeks or more.

The researchers offer two potential mechanisms to explain this connection: one nutritional, the other behavioral. The first suggests that the composition of human breast milk (compared to infant formula) protects against obesity.

For example, they note, “it could be that bioactive compounds such as leptin or ghrelin which have a role in satiety and the negation of hunger occur naturally in human breast milk and are absent in infant formula.”

The behavioral hypothesis suggests that breastfeeding mothers “may be more responsive to children’s cues indicating satiety.” In other words, breast-fed children are more likely to be guided from a very early age to eat when they are hungry and stop when they are full. In contrast, babies encouraged to finish a bottle’s worth of formula may be learning a very different behavior—one with harmful long-term consequences.

Either way, these findings are “tantalizing,” according to the researchers, in that they point to a teachable behavior that “has the potential to improve the health of the population.” True enough. Now if we can only remove some of the practical barriers that make it difficult for many mothers to perform this most natural of acts.