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"Breast-feeding for longer durations appears to have a protective effect against the early signs of overweight and obesity," said lead researcher Stacy Carling, a doctoral candidate in nutrition at Cornell University, in Ithaca, N.Y.
Carling and her colleagues followed 595 children from birth to the age of 2. They tracked the children's weight and length over this time, and compared individual children's growth trajectories to how long the children breast-fed.
Children at the highest risk for gaining extra weight included those with overweight or obese mothers, mothers with lower education levels and mothers who smoked during pregnancy. Almost 59 percent of the children at risk for being overweight had mothers with one or more of these characteristics, compared to about 43 percent of the children not at risk for excessive weight gain.
Among those children with a higher risk for obesity, babies who breast-fed for less than two months were more than twice as likely to gain extra weight than those who breast-fed for at least four months.
The findings were published in the January print issue of Pediatrics.
The study could not prove that breast-feeding caused the reduced risk for obesity. But there are several reasons why the link between breast-feeding and lower obesity risk may exist, the study authors noted.
"Breast-feeding an infant may allow proper development of hunger and satiety signals, as well as help prevent some of the behaviors that lead to overweight and obesity," Carling said.
"Breast-feeding, especially on demand, versus on schedule, allows an infant to feed when he or she is hungry, thereby fostering an early development of appetite control," she said. "When a baby breast-feeds, she can control how much milk she gets and how often, naturally responding to internal signals of hunger and satiation."
Dr. Lori Feldman-Winter, a professor of pediatrics at Cooper University Hospital, in Camden, N.J., pointed out that in addition to better self-regulation in eating, the composition of breast milk is less likely to lead to obesity as well.
"The microscopic properties of human milk regulate metabolism and reduce risk of obesity," Feldman-Winter explained.
The study did not include information on whether the babies were exclusively breast-fed or how often they were getting milk at the breast versus from a bottle, but the time required to reduce obesity risk was not long.
"The difference of two months of breast-feeding may be enough to reap some benefit," Carling said.
Yet the list of reasons mothers do not breast-feed is long and diverse, she added.
In this study, mothers less likely to breast-feed for four months included younger mothers, those with less education or lower incomes, mothers who did not plan to exclusively breast-feed when they were pregnant and mothers who rated their career and work life as highly important.
Improving breast-feeding rates among these mothers would require multiple layers of support, Carling said.
"Ultimately, increasing breast-feeding rates in the United States means increasing knowledge and support at a variety of levels from institutional to interpersonal," Carling said. "Our study recognizes the benefit of longer duration breast-feeding in a specific population and, hopefully, this and other studies will lead to more customized breast-feeding promotion in those populations at higher risk for overweight and obesity."
The study was funded by the U.S. National Institutes of Health, and the authors reported no conflicts of interest.
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