A woman who had gone to the doctor to treat a bacterial infection in her intestines experienced rapid weight gain after the procedure — suggesting that gut bacteria might play a vital role in the body’s metabolism.

The case was recently analyzed in the journal Open Forum Infectious Diseases, and it involved a 2011 fecal transplant to deal with a woman’s C. difficile infection, according to a Fox News report.

The woman was 32 and weighed just 136 pounds, and the donor was her teenager daughter, who was overweight but healthy. Just over a year later, the woman had packed on 38 pounds, and three years later she weighed 177 pounds despite going on a medically supervised diet and exercise program.

It is leading doctors to wonder whether they may have inadvertently removed “good” bacteria during the procedure, causing an extreme change in her metabolism.

Other factors could have led to the weight gain, such as the use of antibiotics and genetic factors, but the woman had never been overweight until she had the surgery. Also, scientists have long suspected a link between gut bacteria in the gastrointestinal tract and weight gain. Studies involving mice show that fat increases when certain bacteria are removed.

The case led the paper’s authors to suggest that doctors be more careful about who is allowed to donate to deal with the C. difficile infection, avoiding those who are overweight. Just last year, the U.S. Food and Drug Administration expressed concern over the safety of fecal transplants to deal with C. difficile infections, even though they appear to be an effective way to treat people with the disease.