Aug. 21, 2012 -- Taken together, two new studies point to a potentially new culprit in the obesity epidemic: antibiotic use.
Antibiotics, especially when taken by infants less than 6 months old, may shift the balance of bacteria in the gut and may set the stage for obesity. The first study, which appears in the International Journal of Obesity, found that infants treated with antibiotics before 6 months of age were 22% more likely to be overweight when they were just over 3 years old.
A related study in mice showed that antibiotics affect gut bacteria involved in digesting nutrients, resulting in increases in fat mass. These findings appear in Nature.
“Typically, we think of obesity as a byproduct of an unhealthy diet and lack of physical activity. This study suggests a broader paradigm,” says Leonardo Trasande, MD. He is an associate professor of pediatrics and environmental medicine at the New York University Langone School of Medicine and a researcher on the first study. “Antibiotic exposures in early life disrupt the flora in our intestines, and that may influence how we absorb calories.”
Weight Gain Associated With Antibiotics
The effects tended to wane when antibiotic exposure occurred outside of 6 months, the study shows.
So how much of an effect are we talking about?
Early antibiotic exposure is a “modest contributor” to obesity risk, Trasande says. “Every contributor identified to date, including sugar-sweetened beverages, unhealthy diet, and lack of physical activity, all seem to contribute very small percentage points to the obesity epidemic.”
The findings re-emphasize the importance of avoiding the overuse of antibiotics, which has also been linked to a rise in antibiotic-resistance and the development of superbugs.
Ilseung Cho, MD, an assistant professor of medicine at NYU’s Langone School of Medicine, was one of the researchers on the paper in Nature. Cho and colleagues developed a mouse model to illustrate exactly how antibiotics may change the gut microbiome and pave the way toward obesity.
A microbiome refers to a community of bacteria in the gut. The study “adds to our knowledge that the gut microbiome is important for health and disease, and that changing the microbiome may be related to obesity.”
Is it the only cause or even a major cause? No, Cho says. “Obesity is caused by a multitude of factors -- poor diet, sedentary lifestyles, and genetics -- but this is also a factor that many people may have underestimated. While antibiotic resistance is one of the biggest risks associated with overuse of antibiotics, it may not be the only risk.”
Scott Kahan, MD, MPH, says the study is a step forward in understanding the relationship between antibiotics and obesity. He is the director of the National Center for Weight and Wellness in Washington, D.C.
“There have been thoughts and preliminary studies in recent years about the possibility that certain bacteria, viruses, or antibiotics could be one of the factors playing into the obesity problem,” he says. "This takes us a little bit further, but it's far from definitive."
The study should encourage people to rethink some of their preconceived notions about obesity. “Many things play a role. It’s more than just lack of willpower that causes a person to be overweight or obese,” he says.