Full of crap? Fecal transplants' dirty little secrets

Let’s face it: Fecal microbiota transplants (FMTs) have been a hot topic for over a decade, touted for their ability to treat recurrent C. difficile infections and other gut-related issues. But there may be more to the story than just replacing bacteria.

Potential health consequences of fecal transplants

A new study in Cell involving mice revealed that microbes transplanted from the colon can colonize the small intestine and upper gut—where they don’t belong—and stay there for months. ^[]

These misplaced microbes altered the physiology of their new home—modifying metabolism, gene expression in the liver, energy regulation, and even behavior.

“There are microbes along the entire intestinal tract, and we just study predominately the last third of it (the colon), so, how can you expect [a transplant], with microbes from a third of the intestinal tract at the end of it, to fix the rest of the intestine?” said lead study author Orlando “Landon” DeLeon, PhD, in a statement. ^[]

What this means for humans isn't clear, but the study authors advise for more caution to be taken with fecal transplants in the future. They suggest an approach that would transfer microorganism from every region of the intestine—not just the colon.

“We have absolutely no idea what’s in FMT, except that it’s a combination of microbes,” said Eugene Chang, MD, senior study author, in a statement. “But even a single FMT will cause a change in the host-microbe relationships in these very different regions of the bowel that may be very difficult to reverse.” ^[]

This isn’t just confined to academia—doctors in the trenches should be aware of how these issues might impact real-world practice. While FMT remains approved by the FDA for C. diff, the organization already issued safety alerts for FMT in 2019 after two patients died from infections transmitted through donor stool. ^{[] []}

The wild world of DIY fecal transplants

Of course, not everyone is getting FMT in a clinical setting. One patient with Crohn’s disease tried a home-brewed transplant—injecting himself with his mother’s feces in an attempt to calm his gut inflammation. ^[]

Meanwhile, some new moms have taken to feeding their infants “poo milkshakes”—breast milk mixed with their own stool—to try to pass on healthy gut bacteria. ^[]

And if that’s not enough to turn your stomach, consider the latest skincare trend: smearing poop directly onto the face. Yep, some people are hoping that microbes in feces might somehow rejuvenate skin. ^[]

What should docs do?

For physicians, the takeaway is clear: Patients are experimenting with these gut-focused therapies far outside of medical guidelines.

As FMT’s potential downsides become more apparent, there’s an urgent need to counsel patients on the real risks involved.

Even in regulated clinical trials, screening donor stool for pathogens and assessing patients for susceptibility to metabolic shifts is critical.

And when patients show up at your office asking whether a “poo milkshake” or a DIY transplant is worth the risk? Well, it’s safe to say the answer is probably no.