"It's just a reality check that in itself, promoting breastfeeding, while a good thing and will have other health benefits, is unlikely to have any effects on stemming the obesity epidemic," said the study's lead author, Richard Martin, from the University of Bristol, UK.
Past research has suggested babies who are breastfed are less likely to grow up to be obese children. But those studies compared mothers who chose whether or not to breastfeed - so they and their kids could have been different in other important ways, researchers said.
The new study included 17,000 mothers and their infants in Belarus. About half of the babies were born at maternity hospitals that used a World Health Organization-designed initiative to promote breastfeeding.
All mothers originally breastfed their babies, so the study was meant to compare how long infants were breastfed, rather than whether they were breastfed at all, Martin noted.
The program to encourage breastfeeding seemed to work - by three months out, 43 percent of mothers who gave birth at intervention hospitals were still exclusively breastfeeding, compared to six percent of women in the comparison group.
Martin said that over the years, his team's study has found fewer stomach infections and eczema and better thinking and memory skills among kids in the breastfeeding-promotion group.
In this stage of the trial, however, the researchers compared weight and body fat in about 14,000 children who were tracked through age 11 and found no differences tied to breastfeeding. Between 14 and 16 percent of all the kids were overweight and about five percent were obese, the team reported Tuesday in the Journal of the American Medical Association.
Dr. Ruth Lawrence, a breastfeeding researcher from the University of Rochester Medical Center in New York, said she still believes that starting breastfeeding in the first place can help ward off obesity. She said past studies have shown breastfed babies have more appetite control than those started on formula, for example.
"Of course it's disappointing that there wasn't a dramatic difference," Lawrence, who wasn't involved in the new study, told Reuters Health.
Researchers said the study doesn't detract from the importance of breastfeeding, given its other known benefits for mothers and babies.
"There's no evidence from this to say you shouldn't continue to follow current recommendations, which are to breastfeed for six months, and breastfeed exclusively," Martin told Reuters Health.
Alison Ventura, a nutrition scientist at Drexel University in Philadelphia, agreed.
"Maybe we shouldn't be touting breastfeeding as an obesity prevention method, but it's still important," Ventura, who wasn't part of the research team, told Reuters Health.
She recommended that new parents learn about when they should introduce certain foods to their baby's diet, and in what portions, as part of thinking about promoting healthy growth long-term.
"Breastfeeding is just one factor," she said, "and maybe studies like this suggest that it's not just one factor that is going to reduce obesity rates, it's probably more the combination of factors."
This website includes materials that are protected by copyright, or other proprietary rights. Transmission or reproduction of protected items beyond that allowed by fair use, as defined in the copyright laws, requires the written permission of the copyright owners.