Diet (animal products) and the Gut Bacteria: A Protective and Non-Protective Mechanism?

Lately, I’ve been reading more and more about biome inhabitants that have both good and bad effect.  I first introduced you to the word pathobionts in 2018 which is used to describe them.  Last week, I wrote about the sometimes-probiotic bacteria, L. reuteri, and MS.  A year ago. I wrote about the two faces of B. fragilis.  I find this idea truly fascinating.

Another interesting story I’ve been following for my own edification: have you ever wondered why it is that “animal products” are associated with higher rates of cardiovascular disease?  In the last few years it was discovered that this is, at least in part, because such foods are high in a compound called trimethylamine, which is converted into trimethylamine-N-oxide, known as TMAO for short.  TMAO promotes a buildup of fatty plaque in arteries, leading to atherosclerosis, which, in turn, can cause heart attacks and strokes.  The parties responsible for the production of TMAO?  You guessed it:  gut bacteria.

Today’s research, out of Oregon State University, shows that a common gut bacterium – one which is actually sometimes associated with inflammation, gut abscesses, bowel diseases and cancer – actually has an important beneficial effect as well.[i] This is a weird one.

First, a little background:  animal products contain the nutrients choline and carnitine.  Unto themselves, these are actually pretty important for health.  Carnintine, for example, is a transporter of fatty acids into the mitochondria of cells, which are used for energy.  It also happens to be a food for many gut microbes, and when these bacteria metabolize it, they produce TMAO. In the research I’m covering today, the scientists discovered that bacteria of the Bilophila genus, which are associated with meat consumption, can take TMA (and its precursors) and metabolize it without producing harmful TMAO.  As the lead researcher states, “That means those bacteria are in effect severing a key link in the cardiovascular disease chain.”  Their evidence suggests that something in the bacteria’s genetic code allows them to avoid making TMAO.  These bacteria are commonly present in people but for those who consume an animal-based diet, levels of the bacteria rapidly rise.

They conclude that their findings suggest that Bilophila’s role in health may depend upon context and certainly more research needs to be done to find out what their role might be as a probiotic in mitigating the negative effects of a  diet high in animal proteins.  It does make me wonder why, if levels go up when people eat meat, TMAO would ever be a problem.   Perhaps it has to do with the level of meat consumption or the level of Bilophila?  Or perhaps there are other cofactors in the gut, like other bacteria?  Time will tell – and since most people have no intention of giving up meat, and the rates of cardiovascular diseases continue to rise in the industrialized world, this is certainly a continuing story I’ll keep an eye on.

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[i] Veronika Kivenson et al. An Expanded Genetic Code Enables Trimethylamine Metabolism in Human Gut Bacteria, mSystems (2020). DOI: 10.1128/mSystems.00413-20