Tuesday, April 9, 2013

Red Meat, Carnitine, TMAO, and Cholesterol

I wrote recently about blueberries and strawberries and their link to heart health. It is thought that berries promote cholesterol cleanup. Now we find that red meat may have the opposite effect.

The specific component of red meat that creates this effect is carnitine, a chemical combination of two amino acids. Gut bacteria that thrive on carnitine produce trimethylamine N-oxide (TMAO) in huge quantities after a person eats red meat. This creates a spike in blood levels of TMAO, and in blood vessels, it appears to block cholesterol cleanup.

This is the interesting part: it is not the red meat itself that creates the TMAO spike. It is the gut bacteria. If you eat red meat almost every day you have lots of this kind of bacteria, and you are guaranteed a TMAO spike every time you eat red meat. If you eat red meat only occasionally, you don’t have the same bacteria and you don’t get a TMAO spike when you eat red meat.

This is some of the best evidence yet that it matters what kinds of digestive bacteria you have, and that what you eat largely determines what digestive bacteria you have. There are other reasons not to eat a lot of meat, but for this particular effect the key is not to eat red meat day after day.

Here is another twist: carnitine is a popular food supplement, thought to promote weight loss, reduce asthma symptoms, and ironically, prevent heart attack recurrences. There is every reason to imagine that carnitine as a supplement feeds the same gut bacteria that thrive on red meat. Many people take food supplements every day, but that seems a risky way to use carnitine. Perhaps the most problematic scenario is the combination of daily carnitine supplements and occasional large meals of red meat.

As a general rule, it is better not to have strong tendencies in the way you eat and live — if you spend much of your time trying to repeat the same things, it can turn into a rut. The carnitine-TMAO connection is just the latest illustration of why this is so.