Breastfeeding moms with healthy eating habits have slimmer infants, who could then be protected from obesity later, researchers say.
Rapid weight gain and fat accumulation during an infant's first six months of life is a risk factor for obesity later on, they explained.
"A baby who is shooting up through the percentiles in weight-for-length during the first six months is two to three times more likely to become obese as early as adolescence," said study author Ellen Demerath, a professor of public health at the University of Minnesota.
She and her colleagues investigated the effect a nursing mother's diet has on infant growth and body fat.
Their study included 354 mothers who were breastfeeding exclusively. They were asked about their eating habits during pregnancy and at one and three months after giving birth.
Children of mothers who had a healthier diet at any of those points were slimmer, weighed less and had a lower body fat percentage in the first six months than those whose moms had poorer diets.
A mother's diet did not affect how much fat-free tissue, including bone and muscle, the child had, according to the study published recently in the journal Nutrients.
"This is evidence that breastfeeding mothers with high-quality diets may help their babies be slimmer and have lower-percent body fat than those who have lower-quality diets, while also supporting healthy growth in length and lean body mass. This bodes well for their risk of obesity later in life," Demerath said.
The next step is to find out what it is in breast milk that could help infants have healthy size and body composition as they grow.
That information could help mothers decide what to eat to make the most nutritious milk, according to Demerath.
About 1 in 5 kids in the United States between ages 6 and 19 is obese, according to the U.S. Centers for Disease Control and Prevention.
The American Academy of Family Physicians has more on children and weight.