British science writer Ed Yong's new book I Contain Multitudes: The Microbes Within Us and a Grander View of Life is a history of gut flora and bacteria, which first entered our consciousness as a scourge to be eliminated and has lately become something between a cure-all (see the universe of "probiotic" food supplements) and a superfood (think of the fecal transplants that have shown such promise in treating a variety of debilitating and dangerous health conditions).
In an NPR interview, Yong runs down the truth, promise and speculation of microbial science and therapy. Long and short of it: eat a lot of fiber, use turd transplants to treat c diff infections, and they may or may not work for IBS and related conditions.
The results are very clear for treating infections of Clostridium difficile, a very hardy bacterium that causes recurrent and often intractable cases of diarrhea. Fecal transplants have been used to treat this condition many times over in many countries. It's been tested in randomized controlled studies, which is the gold standard. The first trial had to be stopped early because [the transplants were so successful that] it seemed unethical to not put all of the patients on this treatment.
That said, the results for other conditions like irritable bowel syndrome and inflammatory bowel disease have been far more inconsistent. That's because C. diff. is kind of a special case. It's a very invasive microbe that has repeatedly been assaulted by antibiotics which have caused a collapse in other microbes. So it's an easy environment for [microbes in] a donor stool to invade.
It might just be that C. diff. was the low hanging fruit. That said, fecal transplants are arguably our most successful microbiome-based therapy. They show some important principles that we might like to take heed of like the fact that [the treatment] is a community-based approach. There are lots of questions to be answered. [For example], we don't know what the long-term risks are, if any.
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