(CNN) — We've heard a lot about the benefits of breastfeeding, and the idea that it reduces the risk of a child becoming overweight or obese has been around for decades.
But a new study in the Journal of the American Medical Association contradicts that idea. It suggests that though breastfeeding has many benefits, reducing the likelihood that a child becomes obese or overweight may not be one of them. The evidence to support this conclusion is strong as the study was based on a large randomized controlled trial.
This study was conducted in Belarus at maternity hospitals and the clinics affiliated with them.
Researchers initially looked at information about more than 17,000 pairs of mothers and infants who were breastfeeding. Of them, about 14,000 participated in the follow-up period between January 2008 and December 2010; the children by that time were around 11 years old.
Only healthy, singleton babies who were born weighing at least 2,500 grams (5.5 pounds) were included in the research. Their mothers had initiated breastfeeding and didn't have any conditions that could impact their ability to breastfeed.
This was a randomized controlled study, meaning it is unlikely that other factors besides the breastfeeding intervention influenced the outcomes, said Richard M. Martin, lead study author based at the University of Bristol's School of Social and Community Medicine.
Sixteen of the health facilities were randomly chosen to receive a breastfeeding intervention based on the Baby-Friendly Hospital Initiative, which the World Health Organization and United Nations Children's Fund developed. This initiative helps mothers to start breastfeeding soon after birth and demonstrates breastfeeding to new mothers.
The other 15 clinics did not receive the intervention. Instead, they proceeded with their standard practices, which included early introduction of non-breast liquids and promoting scheduled breastfeeding rather than breastfeeding on demand. "The mothers weren't encouraged to breastfeed early on," Martin said.
Those who received the intervention were more likely to breastfeed longer, compared to those who were not exposed to the breastfeeding initiative. At 3 months, babies whose mothers received the intervention were seven times more likely to be exclusively breastfed, and twice as likely to be predominantly breastfed.
When the children were older, researchers didn't find a significant difference in the weight of the children. Breastfeeding also did not appear to influence levels of later-life serum insulin-like growth factor, a natural chemical that regulates a child's stature and body composition.
Although the intervention appeared to promote breastfeeding, it did not appear to lower the prevalence of children who were overweight or obese. Keep in mind Belarus has a lower incidence of obesity than the United States.
Previous research published by Martin and colleagues from the same trial did document benefits of breastfeeding. They found that in the first year of life, children who were breastfed others had less-frequent gastrointestinal infections and eczema than those who were not. Around age 6, they tended to have higher scores on IQ tests.
"Efforts to promote, protect and support breastfeeding should continue," Martin said.
But for policy-makers aiming to reduce the levels of obesity across a population, they may want to focus on other efforts; breastfeeding may not be an effective one, Martin said.