A new study has come to a surprising conclusion: children may be gaining significant weight due to antibiotics they are taking.

A study of 164,000 children in Pennsylvania found that kids at age 15 who were prescribed antibiotics at least seven times in their childhood were, on average, 3 pounds heavier than other children, according to a Wall Street Journal report.

Brian Schwartz, the lead author of the study and a physician and epidemiologist at the Johns Hopkins Bloomberg School of Public Health, said that antibiotics at any age appear to be connected to weight gain. His research was published in the International Journal of Obesity this week.

Antibiotics have been tied to weight gain before — farmers even feed them to their animals in order to cause them to put on weight and thus boost their profits.

It appears to have the same effect on humans, including children. Studies indicate that children who are 1 or 2 years of age and get antibiotics tend to gain weight.

Why is this the case? Possibly because antibiotics kill bacteria in the gut in such a way that it breaks down the food differently, resulting in more food being stored by the body and thus more fat reserves.

Antibiotics, also referred to as antibacterials, are a treatment for bacterial infections. They are aimed at killing bacteria or at least inhibiting their growth. They can be extremely powerful and thus are used in the medical community carefully. One of the most common antibiotics, penicillin, was discovered in 1929 when he noticed spores of green mold on his culture plates.

A news release on the findings were published on Johns Hopkins’ website, which can be found here.