One woman experienced sudden and unexpected weight gain after a fecal transplant from an overweight donor. Photo by bikeriderlondon/Shutterstock

PROVIDENCE, R.I., Feb. 4 (UPI) -- The medical process known as fecal microbiota transplantation (FMT) -- often simply called a stool or fecal transplant -- has garnered quite a few headlines and accolades as a way to restore healthful gut bacteria and as a treatment for patients diagnosed with a problematic Clostridium difficile infection (CDI).

But a new case study warns that even a successful fecal transplant can have unintended and unhealthy consequences, like rapid weight gain.


According to a new report published in the journal Open Forum Infectious Diseases, a woman who had always been of a healthy weight quickly became obese in the wake of a fecal transplant from an overweight donor.

Prior to the woman's 2011 fecal transplant, she weighed 136 pounds and registered a Body Mass Index (BMI) of 26. To treat ongoing CDI-related diarrhea problems, the woman received a fecal transplant from her overweight but healthy daughter, via colonoscopy. Sixteen months later and the woman was clinically obese, weighing 170 pounds with a BMI of 33. Her weight gain continued despite a medically supervised liquid protein diet and exercise regimen.

"We're questioning whether there was something in the fecal transplant, whether some of those 'good' bacteria we transferred may have had an impact on her metabolism in a negative way," Dr. Colleen R. Kelly, a researcher at the Warren Alpert Medical School of Brown University, said in a press release.

Kelly and her colleagues say there are other potential explanations for the woman's rapid weight gain. The patient was also being treated with a number of antibiotics for another gut infection (Helicobacter pylori). It's also possible the eradication of her Clostridium difficile infection encouraged her to quickly amass extra pounds.

Still, researchers say the phenomenon is unique enough to warrant extra attention and a reminder that the long-term effects of fecal transplants (an increasingly popular medical procedure) need to be studied more closely.

"Careful study of FMT will advance knowledge about safe manipulation of the gut microbiota," authors of the new study wrote. "Ultimately, of course, it is hoped that FMT studies will lead to identification of defined mixtures of beneficial bacteria that can be cultured, manufactured, and administered to improve human health."