Breastfeeding has many benefits for babies, but protection from obesity may not be one of them, a UK research team reports.

Instead, the researchers say, the protective effect of breastfeeding some studies have found is likely due to the fact that women who breastfeed their infants also tend to have qualities that make them less likely to raise obese children.

“There are several reasons for why mothers should breastfeed their children, independent of obesity,” Dr. Andre M. Toschke of Kings College London, the study’s lead author, told Reuters Health. “(Our) study questions a little bit the argument of breastfeeding for protection against obesity.”

To better understand the breastfeeding-obesity link, Toschke and his team used a technique called dual-energy X-ray absorptiometry (DXA) to measure fat mass in a group of 4,325, 9- to 10-year-olds. Most studies to date have used body mass index (BMI) to measure overweight, which is less precise, the researchers note in the June issue of the American Journal of Clinical Nutrition.

Children who were breastfed, who represented 82 percent of the total, had lower fat mass percentages. But once the researchers used statistical techniques to control for factors linked to both breastfeeding and obesity risk, including mother’s education and socioeconomic class, maternal BMI, time the mother spent watching television daily, and time spent in a car for each weekday, the effect of breastfeeding was weakened.

The association did remain strong, however, for children who had been breastfed for six months or longer. They were 55 percent less likely than their non-breastfed peers to fall into the top tenth of the group based on body fat percentage.

To get a definitive answer on whether breastfeeding truly protects children from becoming overweight later on, it would be necessary to randomly assign mother-infant pairs to breast or bottle-feeding, which would be unethical, Toschke said.

But studies of breastfeeding promotion interventions with adequate follow-up could also help answer this question, he added, and would be free of the confounding factors at play in other research.

SOURCE: American Journal of Clinical Nutrition, June 2007.