I've seen a flurry of published fecal microbiota transplantation papers lately -- and just in case anyone is getting the wrong idea (erm, biohackers), I want to emphasize: FMT is interesting to study at this point but it is rarely the endgame.

Yes, FMT is a treatment for critically ill people who have recurrent C. difficile infection. It can be lifesaving in that context...

But in a research sense, FMT -- in animals and then in humans -- is merely a crude way to find out whether even a *smidge* of causality can be attributed to the gut microbiome in a certain disease or condition. This is where the field is right now.

As these researchers point out, FMT from humans seems to induce a disease almost *every time* in mice: https://www.cell.com/cell/fulltext/S0092-8674(19)31387-X

But humans are more complex. If a study shows FMT is associated with some clinically detectable difference in a disease, it's a sign that a follow-up study should be planned. It's not a sign that FMT is suddenly a valid DIY treatment for that disease.

I think researchers understand this when they design FMT studies... but it's important to make this clear to members of the general public who may be hearing about the research.