Do Antibiotics Cause Weight Gain?

The antibiotics you’re taking to tackle that sinus or chest infection may be a factor in weight gain. Ranchers have known since the 1940s that giving cattle regular low doses of antibiotics improves the amount of weight cattle gain for every pound of food given. A study in Nature helps explain why.

The study showed that after giving mice regular low doses of antibiotic for seven weeks, a change took place in the gut microbiome. (The microbiome is a trendy name given the millions of bacteria that live in our gut and elsewhere in our body.) The mice in this study gained 10-15% more weight, which means the antibiotic made the mice more efficient at extracting energy out of food. The team of researchers also analyzed data from a study of infants born in 1991-92, to look for a correlation between antibiotic exposure and children’s weight. The study involved 11,000 children under six months of age, and investigators found that babies who had been exposed to antibiotics had a 22% chance of excess weight.

For some, this finding raises another question. What about very low levels of antibiotics in meat we consume? ”We may not understand the biological relevance of exposures through consuming meat at those levels,” says Keeve Nachman, who researches antibiotic use in the meat industry for the Johns Hopkins Center for a Livable Future. Clearly, as they say, more research is needed.

Click here to read more in Mother Jones, click here to read the mouse study in Nature, and click here to read the study of infants exposed to antibiotics.

Methicillin-resistant Staph image by NIAID / Wikimedia.