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Woman becomes obese after fecal transplant from overweight donor

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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.

Reddit comment:

It's a very interesting question and something that we don't understand well at all yet. A great place to start if you're interested is Martin Blaser's book "Missing Microbes." It's well-written and has a pop-sci feel so it's very approachable for non-microbiologists.

Brief summary: All animals have a resident microbial community, with which they share a long evolutionary history. Due to some very recent (biologically speaking) changes, include increased C-section rates (no longer colonized with maternal bacteria passing through the birth canal, so gut microbiome differs between mother and child more in C-section than natural delivery parents), clean food/water (less H. pylori "infection"), and perhaps decreased parasite burden, microbial community structures today are thought to differ greatly from what they did 100 years ago. There is some moderately strong evidence that taking even 1-2 courses of certain antibiotics as a child (esp. tetracyclines) may increase the risk of obesity later in life, as it may impact and alter community composition. This is NOT to say that antibiotics aren't fantastic, just another reason that we should be more judicious in their use than we currently are.

Dr. Blaser made his reputation studying H. pylori, so he naturally focuses there and proposes that as H. pylori infection rates decrease, stomach acid production increases, so it is easier for "foreign" bacteria to take up residence in the human gut tract, which may lead to obesity. The key players right now are thought to bacteria in the Bacteriodes and Firmicutes groups based on murine models and some studies in humans that showed that different ratios of these two main groups are associated with differences in body weight.

Unfortunately, we know next to nothing about this very complicated ecosystem, so it's impossible to say anything definitive at this point. However, I wouldn't be surprised if many medical advances in the next 20 years don't develop out of this current work on the microbiome, potentially including a "cure" for obesity (but that is pure speculation). It's a really exciting field and I'm glad to see it getting attention!

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