Sunday, November 02, 2014

Romanticising the microbiome

There's a really good Ed Yong piece at the New York Times which argues convincingly that there is a lot of premature excitement about the possibilities of influencing health by deliberately altering the gut microbiome.  Sure, fecal transplants work for one particular problem, but the fact that  gut bacteria are changing rapidly all the time anyway means it's no simple task to fix other problems.

You should read the whole thing, but I found this section particularly interesting:
Take the Hadza. Their microbial roll call is longer than a Western one, with both omissions and additions. They are the only adult humans thus far sequenced who are devoid of Bifidobacteria — a supposedly “healthy” group that accounts for up to 10 percent of the microbes in Western guts. But they do carry unexpectedly high levels of Treponema, a group that includes the cause of syphilis.

Is this menagerie worse than a Western one? Better? I suspect the answer is neither. It is simply theirs. It is adapted to the food they eat, the dirt they walk upon, the parasites that plague them. Our lifestyles are very different, and our microbes have probably adapted accordingly. Generations of bacteria can be measured in minutes; our genomes have had little time to adapt to modern life, but our microbiomes have had plenty.

It may be that a Hadza microbiome would work equally well in an American gut, but incompatibilities are also possible. The conquistadors proved as much. As they colonized South America, they brought with them European strains of Helicobacter pylori, a stomach bacterium that infrequently causes ulcers and stomach cancer, and these European strains also displaced native American ones. This legacy persists in Colombia, where some communities face a 25-fold higher risk of stomach cancer, most likely due to mismatches between their ancestral genomes and their H. pylori strains.
 Yong mentions earlier in the article who the Hadza are:
In September, the archaeology writer Jeff Leach used a turkey baster to infuse his guts with the feces of a Hadza tribesman from Tanzania.....

 He experimented on himself because he views the Western microbiome as “a hot microbial mess,” he wrote on his blog. Poor diets, antibiotics and overly sanitized environments have gentrified the Western gut, he wrote, “potentially dragging us closer to ill health.” The Hadza, with their traditional hunter-gatherer lifestyle, carry diverse microbial communities that are presumably closer to a healthier and disappearing ideal. Hence the stunt with the turkey baster. Mr. Leach billed it as “(re)becoming human.”

This reasoning is faulty. It romanticizes our relationships with our microbes, painting them as happy partnerships that were better off in the good old days.
Yong's a fine science writer.

1 comment:

John said...

I think he is right. It is not uncommon in biomedicine for fads to happen. I'm more interested in the microbiome from a symbiotic point of view than a health angle. Fact is our gut flora change very quickly so it seems unlikely to be a major health issue. I regard it is a generally very lower order causation.