FMT Donor BMI Not Correlated to Recipient Weight Gain

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Fecal microbiota transplantation recipients did gain weight following the procedure.

New research shows fecal microbiota transplantation (FMT) donor body mass index did not necessarily correlate with weight gain for recipients.

A team, led by Kanika Sehgal, MBBS, Mayo Clinic, determined if there was a change in recipient body mass index following fecal microbiota transplantation corresponding with donor BMI.

Fecal Microbiota Transplantation

FMT is considered a top treatment for recurrent clostridium difficile infections (CDI), with evidence suggesting human metabolic profiles could be influenced by the treatment. In addition, recent studies found body mass index of donors can also influence the BMI of recipients.

The investigators identified patients who underwent FMT at the Mayo Clinic between August 2012 and August 2019 using a maintained database.

They also recorded the demographics of recipients and corresponding donors using the same database and extracted recipient BMI 1 year before and after FMT and donor pre-FMT BMI measurements from a query of electronic medical records.

The investigators also classified BMI between 18.5-24.9 kg/m2 as normal and ≥25 kg/m2 as overweight.

Using mixed linear regression models, the team analyzed trends in BMI changes of the recipients.


Overall, there were 403 patients included in the study with pre- and post-FMT BMI recordings with a median age of 59.1 years for recipients at the time of FMT.

The median pre-FMT recipient BMI was 26.7 kg/m2 and the median donor BMI was 24.5 kg/m2.

In addition, stool from donors with BMI in the normal range represented 58.2% of the transplants, while 41.8% of the recipients received stool from overweight donors.

However, donor BMI information was missing from 3.2% of the recipients.

The investigators found recipient BMI increased by an average of 0.05 per month after FMT within the 1 year follow-up period (95% CI, 0.01-0.09; P = 0.020), while donor BMI did not have a significant effect on recipient BMI change over time (P = 0.24) or the BMI level (-0.18 per donor BMI point; 95% CI, -0.48 to 0.12; P = 0.233).

“Recipient BMI increases post-FMT,” the authors wrote. “However, donor BMI did not correlate with recipient BMI changes post procedure. Recipient weight gain after FMT might be reflective of recovery towards baseline weight.”

High Failure Rates

The investigators expect large, prospective, controlled trials focusing on weight in the context of FMT are needed before finalized conclusions can be made.

Recently, investigators found a high failure rate for potential FMT donors.

A team, led by Yuk Kam Yau, Center for Gut Microbiota Research, Faculty of Medicine, The Chinese University of Hong Kong, examined the outcomes of screening and recruitment of fecal donors for fecal microbiota transplantation.

Potential FMT donors underwent a pre-screening telephone interview, a detailed questionnaire, and blood and stool investigations. Between 2017-2020, the investigators assessed 119 potential donors, 75 of which failed for a variety of reasons including inability to come back for regular and long-term donation (n = 19), high body mass index (n = 17), underlying chronic illness or on long-term medications (n = 11), being healthcare professionals (n = 10), use of antibiotics within 3 months (n = 5), and others (n = 13).

A total of 44 donors completed questionnaires, while 11 participants did not fulfill the clinical criteria. For the remaining 33 donors with both stool and blood tests, 21 failed the stool investigations.

Of this subgroup, 19 had extended-spectrum beta-lactamase (ESBL) organisms, 1 had a Clostridioides difficile infection, and 1 had C difficile with Methicillin Resistant Staphylococcus aureus.

There was also 1 failed blood test due to high serum alkaline phosphatase level, 1 participant who required long-term medication, and 9 individuals who withdrew consent and/or lost to follow-up.

The investigators found only 1 (0.8%) of the entire recruited 119 potential donors was successfully recruited as a regular donor.

The study, “Body Mass Index Changes After Fecal Microbiota Transplantation for Recurrent Clostridioides difficile Infection,” was published online by ACG.