Neha Alang and Colleen R. Kelly recently reported that a patient who had received fecal microbiota transplantation (FMT) developed obesity (1). Although it is impossible to be sure about the role of FMT in this very case, it seems wise to exclude obese donors from FMT.

This 32-year-old patient required FMT for recurrent Clostridium difficile infection (CDI). Before FMT she had some overweight (Body mass index, or BMI, 26 kg/m2) but this increased dramatically after FMT and apparently without etiology. Her BMI was 33 after 16 months and 34.5 after 3 years.

The fecal donor (her daughter) had overweight at the time of FMT (BMI 26.4). Experiments in animal models have shown that FMT from an obese mouse can be associated with transmission of obesity (2,3). It is thus (at this stage) wise, as proposed by the authors and applied in many centres, to exclude subjects with overweight from fecal donation.

Expanding knowledge in this field would also be helpful in knowing whether transferring the microbiota from lean subjects would help obese subjects, and whether some microbiota would help improve specific situations of denutrition.


1) Neha Alang and Colleen R. Kelly. Weight Gain After Fecal Microbiota Transplantation. Open Forum Infect Dis (Winter 2015) 2 (1): doi: 10.1093/ofid/ofv004
2) Ridaura VK et al. Gut microbiota from twins discordant for obesity modulate metabolism in mice. Science. 2013;341:1241214
3) Bäckhed F et al. The gut microbiota as an environmental factor that regulates fat storage. Proc Natl Acad Sci U S A. 2004;101:15718-23.