Within a week, the other shoe dropped. The same researchers that published the first carnitine-is-bad study (Stanley Hazen’s group at the Cleveland Clinic) came out with another paper about lecithin. Expanding on a similar 2011 paper
, this study associated TMAO with heart disease risk in humans. Once again, food (in this case, egg yolks) resulted in higher TMAO levels. The effect was gone, however, after a course of antibiotics.
What’s really amazing here–whether the results hold up or not–is that we are finally hearing about what gut bacteria do
, not just who they are. Many studies on our internal ecosystems are just cataloguing the players, creating a modern-day version of the medieval bestiary
without really understanding how the species interact and what they do for us. The meat-eaters, for example, had guts dominated by Prevotella
bacteria, but who’s to say Prevotella
was the microbe responsible for making TMAO, or even that meat-eating was what caused the TMAO makers to grow in meat-eaters’ stomachs? There is evidence linking Prevotella to consumption of whole grains
, so the dietary culprit, if there is one, could be a meat/grain combo.
There are hundreds of species in our intestines, many of which we can’t grow in the lab, and the tough questions of what exactly they do, how they interact, and how they make use of our food are not ones we are currently able to answer with any sense of completeness. We have crude tools that have only advanced a little since the must-read parables of the geneticist and biochemist
. (I’ll wait while you read the whole thing, but here’s a taste: Trying to understand how cars are made, the biochemist grinds one up and announces that cars are 10% glass, 25% plastic, 60% steel, and 5% other. Meanwhile, the geneticist ties the hands of workers going into the factory and examines how and whether the resulting cars crash. He concludes that seatbelts are vestigial since the cars still function without them.)
The other reason these studies are hard to wrap our heads around, aside from the sheer complexity of the question (what else was in that steak, anyway? Does it matter if it was grass-fed or factory farmed? How similar is one carnivore’s gut microbiome to another’s?) is that we like answers we can act on now
. I can read a study about steak today and switch to veggie burgers tomorrow. Messing with diet is popular because it’s totally within our control and we can do it three times a day. Popping a pill is not much more of a commitment, but understanding the metabolic pathways of a collection of symbiotic organisms? That’s going to take a little longer.