When women who were obese prior to becoming mothers followed national breast-feeding recommendations, they weighed almost 18 pounds less than obese mothers who didn't breast-feed. If mothers were overweight or had a normal weight before pregnancy, their weight six years later didn't appear to be related to whether they breast-fed their children or not.
While this study was able to link weight loss in obese mothers and breast-feeding, it could not show that breast-feeding caused the weight loss. Still, Dr. Lori Feldman-Winter, pediatrician and a professor of pediatrics at Children's Regional Hospital at Cooper University Health Care in Camden, N.J., said it's definitely possible that it contributed.
"Breast-feeding not only burns extra calories but it also changes the metabolism through a series of hormonal effects required to lactate," Feldman-Winter said. "The full understanding of how breast-feeding leads to improvements in metabolism for both mother and her baby is incomplete, but there are multiple epidemiological studies showing the association."
Feldman-Winter, who reviewed the findings but was not involved in the study, said that women who are not obese may also experience a metabolic benefit from breast-feeding. But, because they are less likely to try to lose much weight, a study would require a much larger group of women to see the possible effects in weight loss for those women, she said.
"It is not clear why we did not observe an association among normal-weight or overweight mothers," said the study's lead researcher, Andrea Sharma, an epidemiologist at the U.S. Centers for Disease Control and Prevention in Atlanta.
Lifestyle might be a possible reason why obese mothers experienced a weight loss benefit.
"Many mothers choose to eat a healthier diet when breast-feeding, and through these dietary modifications, they may actually improve their overall diets and therefore achieve a more healthy weight," Feldman-Winter said.
Results of the study were published online Sept. 2 in the journal Pediatrics.
The researchers tracked more than 700 women six years after they gave birth and compared weight retention between those who did and did not breast-feed. Weight retention was the difference between the women's pre-pregnancy weight and their weight six years after giving birth.
Women were considered obese in this study if they had a body mass index (BMI) of 30 or greater. BMI is a measurement used to estimate fat levels and assess whether a person has a healthy weight for their height. A BMI below 25 is considered normal, and a BMI between 25 and 30 is considered overweight.
At the time the women gave birth (2005 to 2007), the American Academy of Pediatrics (AAP) recommended that women exclusively breast-feed at least four months and then continue breast-feeding through 12 months, according to background information in the study.
Almost a third of the women (29 percent) in the study exclusively breast-fed for at least four months, and one in five continued to breast-feed past 12 months. Eighteen percent of the women did not breast-feed at all.
Only obese women who followed the recommendation to breast-feed at least 12 months experienced the weight loss benefit. Obese mothers who exclusively breast-fed at least four months but stopped before one year weighed about 12 pounds less than their non-breast-feeding counterparts, but this finding did not reach statistical significance.
Given that few studies have examined breast-feeding and weight retention for more than a one-year follow-up, this study is an important contribution to understanding the long-term effects of breast-feeding on the mother," wrote Laurence Grummer-Strawn and his colleagues at the CDC in an editorial in Pediatrics that accompanied the study.
Both Sharma and Feldman-Winter stressed that the benefits of breast-feeding for mothers and their babies extend far beyond a mother's potential weight loss. Women who breast-feed have a decreased risk of diabetes, heart disease, breast cancer, ovarian cancer and depression, she said.
"Children who are breast-fed have protection from acute ear infection, gastrointestinal infections, hospitalization for lower respiratory tract diseases in the first year, sudden infant death syndrome, and reduced risk of a number of chronic diseases, including asthma and obesity," Sharma said.
Learn more about the benefits of breast-feeding from the U.S. Office on Women's Health.