A few words here about red meat.
We have all heard for decades that red meat is unhealthy. The original recommendation by the medical community to reduce red meat consumption was based on the (now false) assumption that dietary animal fat was the chief cause of obesity, and heart disease. However, while it is now clear that animal fat (including the fat in beef) is actually healthy in small amounts, good studies continue to link regular consumption of red meat with increased risk of cardiovascular disease. Why?
Red meat is high in a particular compound called carnitine which is synthesized from two amino acids (methionine and lysine). Certain gut bacteria feed on carnitine producing a waste product which is turned into something called TMAO. Recent studies have shown that high levels of TMAO cause tiny puncture wounds form along the cells lining our arteries (the endothelium). These endothelial wounds are the initiating event for plaque formation (atherosclerosis). Humans and animals who eat red meat regularly have higher levels of TMAO which is directly associated with atherosclerosis and increased risk of heart attack.
Should we avoid carnitine then? Not so fast. Carnitine is an essential compound used by all cells of the body for energy and for fatty acid metabolism. It helps muscles heal after injury and intense workouts. Carnitine plays a vital role in health. But like any healthy substance, too much of it can become a problem. Too much carnitine over time results in too much TMAO.
TMAO levels do not go up after eating red meat in people who only eat it occasionally. Vegans given meat/carnitine do not show a rise in TMAO levels because the bacteria which feed off of carnitine die off after prolonged periods without carnitine to sustain them. Animals fed a diet rich in carnitine over time show the same rises in TMAO and the same endothelial ulcers as do humans. However, if these animals are given bacteria-killing antibiotics prior to being fed carnitine, TMAO levels remain low, supporting the idea that gut bacteria are the source of the TMAO.
In a nutshell, certain gut bacteria feed on carnitine which leads to production of TMAO, which in turn damages our blood vessels. This is what makes regular consumption of red meat (the most potent source of carnitine) a risky dietary behavior.
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