Unexpected Weight Gain Post Fecal Matter Transplant

A woman successfully treated with fecal microbiota transplantation (FMT) for recurrent Clostridium difficile(C. difficile) from an overweight donor’s stool found herself quickly gaining weight afterward to the point of obesity, reported a case published in the journal Open Forum Infectious Diseases.

While FMT had been touted as a promising treatment for relapsing C. difficile infections, the case report suggested clinicians should avoid choosing stool samples from overweight donors. Unsurprisingly, the report also inspired questionsregarding the gut bacteria’s exact role in metabolism and health.

As reported in the journal, during the 32-year-old woman’s 2011 FMT procedure, she weighed a stable 136 pounds, and her Body Mass Index (BMI) was 26.

However, upon using donor stool froman overweight, but otherwise healthy, teenager, the woman’s weight, merely 16 months later, increased to 170 pounds, and her BMI to 33 — hitting the benchmarkfor obesity. Despitea strict liquid protein diet and exercise program, her weight gain persisted, and 3 years after the transplant, she weighed 177 pounds with a BMI of 34.5. Even today, she still remains obese.

Colleen R. Kelly, MD, of the Warren Alpert Medical School of Brown University, co-author of the case report with Neha Alang, MD, of Newport Hospital in Rhode Island, weighed in, "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."

The authors specified the link between bacteria in the gastrointestinal tract and weight as supported by prior research with mice models that produced significant fat increase when gut bacteria was transferred from obese to normal-weight mice.

Researchers also noted that the FMT should not be regarded as the sole cause of the woman's weight gain, since aside from C. difficile treatment, she was also treated with several antibiotics for Helicobacter pylori infection. As such, other potential contributing factors to her weight gain include “the resolution of her C. difficile infection, genetic factors, aging, and stress related to illness”.

Ana A. Weil, MD, and Elizabeth L. Hohmann, MD, both of Massachusetts General Hospital, highlighted the significance of monitoring FMT’s long-term outcomes: "Careful study of FMT will advance knowledge about safe manipulation of the gut microbiota. 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."

Until further evidence is procured, the authors recommendedfinding FMT stool donors who are not overweight.