Why are fecal transplants so successful in repairing the gut? Study explores what happens when microbiomes merge

What happens when two gut microbiomes collide? Considering no two gut microbiomes are alike, researchers observed the interactions between microbes of different ecosystems during a fecal transplant. Their research hopes to provide a better understanding of why this fascinating therapy works so well.

Your gut microbiome reflects you—your diet, stress, and physical activity all play a role in shaping what type of microbes thrive and flourish in the gut. For people with Crohn’s disease and bacterial infections, transferring microbes through fecal transplants has helped ease discomforting symptoms. 

The first recorded fecal transplant occurred in fourth-century China and eventually made its way into western medicine in the 1950s. At the turn of the 21st century, gut health became a growing trend, with supplements and diets advertised to give you a happy gut and, therefore, a happy life. The renewed fervor over gut health made its way into the scientific community as well, with scientists investing time and resources towards understanding how this unusual procedure works to treat common gut disorders.

One popular theory is the “super donor” hypothesis. The hypothesis states people with a “good” gut are essential for successful fecal microbiota transplantation, and a good donor can help a variety of patients. Another hypothesis suggests the transferred microbes reverse the damage and bring the recipient’s gut back to a healthy state.

However, the current study offers an alternative explanation. Through studying medical data from 300 fecal microbiota transplantations, the team found it was the recipient, rather than the donor, that determines whether the procedure will be a success or a failure. Microbial diversity in the recipient’s gut and how different both microbiomes are from each other are the main factors influencing whether certain bacteria survive after a transplant.

“Being able to thrive and survive in an entirely new setting is no simple task, especially in a dynamic environment such as the human gastrointestinal tract, where there are constant changes in acidity, oxygen levels, and nutrients, among others,” says lead study author Simone Li in a statement. “As we move towards safer options of microbiome-based therapeutics, what goes in only matters as much as whether they stay long enough to deliver the intended benefits.”

The study dealt with fecal transplants carrying bacteria and archaea, which comprise over 90% of the gut microbiome. “As our understanding of the ecological processes in the gut following FMT improves, we may discover more precise and more targeted links to clinical effects—for example, to displace only specific strains (e.g. pathogens) while minimizing ‘collateral’ effects to the rest of the microbiome,” adds study coauthor Peer Bork.

The researchers note future studies may eventually look at the role of fungi and viruses as well, which play a small but meaningful role in the gut.

The study is published in Nature Medicine.

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