An exotic intestinal infusion

Jeff Leach, at the “Human Food Project”, has written pungently about a bout of microbiome self-experimentation: “(Re)Becoming Human: what happened the day I replaced 99% of the genes in my body with that of a hunter-gatherer”.

AS THE SUN set over Lake Eyasi in Tanzania, nearly thirty minutes had passed since I had inserted a turkey baster into my bum and injected the feces of a Hadza man – a member of one of the last remaining hunter-gatherers tribes in the world – into the nether regions of my distal colon. I struggled to keep my legs in the air with my toes pointing towards what I thought was the faint outline of the Southern Cross rising in the evening sky. With my hands under my hips – and butt perched against a large rock for support – I peddled an imaginary upside down bicycle in the air to pass the time as I struggled to make sure my new gut ecosystem stayed put inside me.

I have to say, this is just wrong.

For one thing, many people around the world carry potentially harmful parasites, from tapeworms to treponema. Shooting these up your anus is a bad idea. Leach admits later in the post that he blithely ignored this risk:

However, I had no data on the parasites he might carrying at the time of the transplant as those analysis were still ongoing at Jack Gilbert’s lab at the University of Chicago. Oh well, parasites be damned, onward with the science!

For another thing, the Hadza have their own long evolutionary history. Their diet is merely one representative of the marked dietary diversity of recent hunter-gatherers. Other foraging groups, for example, the Ache of Paraguay, have a very different dietary composition. The study of these microbiomes is scientifically very interesting, and we may discover commonalities among them. But the idea that the microbiome of any Hadza person represents an “ancestral” or “healthy” human population is nonsense. They have their own distinctive set of challenges affecting their microbiomes, including the aforementioned parasites. A microbial community that has formed within a Hadza gut might work equally well anywhere else, but there’s really no reason to expect that it will.

Scientists are working to establish which aspects of microbial communities may be associated with health outcomes, and an important part of that process is understanding how human populations vary. Westernization of diet is one of the major influences on microbiomes, and studying forager microbiomes is a good idea. Fecal transplants have proven useful in cases of recurrent infection by pathogenic bacteria, and it is possible to imagine that intestinal health or obesity might reflect the action of the microbiome.

Still, there seems to be a lot of quackery here – almost a New Age belief in the power of a gut unspoiled by burgers and fries.