Fecal microbiota transplantation (FMT) involves the transfer of fecal material from a healthy donor to the digestive tract of an ill recipient (most commonly, someone with refractory, or difficult to manage, C. difficile diarrhea). Transplanting the gut microbiota from a healthy individual to someone with C. diff has resulted in an impressive 90+ percent cure rate of the disease. Brenda and I have blogged about this topic a few times.

In a recent paper published in the journal Open Forum Infectious Diseases, Neha Alang, MD, and Colleen Kelly, MD report weight gain in a patient who received FMT from a donor who also gained weight shortly after the donation took place, suggesting that the microbes themselves may be to blame for the weight gain.1

“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,” noted Kelly.

The patient was a 32-year-old healthy, normal weight female who had been unsuccessfully treated for C. diff infection on multiple occasions. Upon discussion of FMT with her physician, she requested that her 16-year-old daughter be the donor. At the time, her daughter’s weight was normal (~140 pounds), but later increased to 170 pounds. The patient improved after the transplant and did not experience a relapse of C. diff.

Sixteen months later, however, the patient had gained 34 pounds and had become obese. She was unable to lose the weight despite dietary and exercise practices. She continued to gain weight—twenty months later she weighed 177 pounds and had developed constipation and indigestion.

The physicians suggest that, due to her previous history of never being obese and the weight gain that had also occurred in her daughter, the obesity may be a consequence, at least in part, of the bacteria transferred via the fecal microbiota transplantation. Animal studies support the hypothesis that an obese microbiota can be transferred and that it can induce obesity in the recipient.2

Unfortunately, there is no baseline stool evaluation to determine what the before and after microbiomes looked like. Fortunately for us, it is possible to evaluate the microbiome of our stool using an affordable test ($89) from UBiome.

As a result of this case study, the physicians have altered their FMT practice policy to require FMT donors be non-obese. This study highlights the importance of rigorous donor selection, and may discourage FMT recipients from choosing family members as donors. This study is yet one more indication that our microbes are truly in control of our health. Or, on the flipside, perhaps one day we will treat bulimia and anorexia with fecal microbiota transplants.


  1. Alang N and Kelly CR, “Weight gain after fecal microbiota transplantation.” Open Forum Infect Dis. Winter 2015 2(1): doi: 10.1093/ofid/ofv004.
  2. Ridaura VK, Faith JJ, Rey FE, et al., “Gut microbiota from twins discordant for obesity modulate metabolism in mice.” Science. 2013 Sep 6;341(6150):1241214.