Americans love their hamburgers, but today, there is more evidence than ever to suggest that eating red meat increases the risk of heart disease — and it has less to do with cholesterol and saturated fat than with trimethylamine N-oxide, or TMAO, a compound made by gut-bacteria during digestion.
Dr. Stephen Hazen of the Cleveland Clinic and colleagues wanted to learn more about how gut-bacteria — the normal microorganisms in the intestinal tract that help break down food — affect cardiovascular health, and the result were surprising. In dual studies, the team discovered that eating red meat causes gut-bacteria to turn choline, carnitine and lecithin, found in abundance in red meat, dairy products and egg yolks, into large amounts of trimethylamine, or TMA.
TMA is then transformed by the liver into TMAO and absorbed by the bloodstream where it contributes to inflammation in blood vessels and the development of unstable atherosclerotic plaques. Together, these processes increase the risk of heart attack, heart failure and stroke.
One unexpected finding, however, was the effect of TMAO on kidney function. Over a five-year period, high levels were shown to play a startling role in the development of chronic renal disease. Dr. Hazen explains that the compound causes the kidneys to become less efficient over time, leading to even higher levels of it in the bloodstream and progressively raising the risk cardiovascular illness.
Study subjects eating red meat saw up to a 10-fold rise in TMAO levels, something not found in vegetarians or those with poultry and fish in their diets. Consumption of eggs and dairy products was not a factor in these studies, but prior research indicates both may also increase levels of TMAO.
There is more research to be done, but these discoveries are shedding light on potential new pathways for treatment. Where known risk factors like high cholesterol don’t fully explain the cause of heart disease, it’s possible that gut-bacteria play a significant part — and when conventional treatments fail, lowering elevated TMAO may be a key to better health.
Until more is known, Dr. Hazen points out that TMAO levels drop within four weeks of eliminating red meat and encourages everyone to continue following current heart-healthy diet recommendations that emphasize fewer animal products and more whole grains, fruits, vegetables and protein-rich legumes.