Red meat, especially processed meat, gets a bad rap, mostly because studies link it with a greater risk for heart disease and some types of cancer. Until now, experts believed the greater risk of heart disease could be blamed on the saturated fat in red meat, but a new study points to another possible cause – a compound called carnitine in red meat.
What is Carnitine?
Carnitine is a compound produced from two amino acids by your liver and kidneys. It’s found in the largest quantity in muscle cells and the cells of your heart. Its function is to transport fatty acids into the mitochondria of cells so they can be used to make ATP as an energy source. Because it plays a role in fat oxidation, carnitine is sometimes promoted as a supplement to help with fat loss, although there’s limited evidence that it works. It’s also an ingredient in some energy drinks and is found naturally in red meat and in smaller quantities in poultry, fish and dairy foods.
Carnitine, Red Meat and Heart Disease
By looking at both mice and humans undergoing cardiac testing, researchers found that carnitine in red meat, energy drinks, and carnitine supplements can be converted by intestinal bacteria to a compound called trimethylamine-N-oxide, or TMAO, once it reaches the intestinal tract. TMAO can then be absorbed and enter the bloodstream. Once it does, it alters cholesterol metabolism in a way that’s not “heart-healthy.” It does this by causing cells lining the inside of arteries to take up more cholesterol and remove less. This acts as a stimulus for atherosclerosis and plaque formation inside blood vessels.
Even more interesting is the fact that red meat lovers who eat beef and other forms of red meat accumulate greater numbers of bacteria that convert carnitine to TMAO. This increases the amount of TMAO the arteries of red meat eaters are exposed to. In contrast, vegetarians and vegans don’t produce significant amounts of TMAO even when they consume carnitine. Researchers believe vegetarians and vegans lack the bacteria that convert carnitine to TMAO because they haven’t eaten red meat and altered the bacteria in their intestines as a result. It’s possible that this explains, at least partially, the fact that vegans and vegetarians have a lower risk for heart disease.
Would Probiotics Make a Difference?
Since intestinal bacteria convert carnitine to artery-clogging TMAO, it’s possible that probiotics might alter the types of bacteria that dwell in the intestinal tract and reduce the conversion of carnitine to TMAO, but that’s a topic for future research. Until then, it’s important to know that it’s not just the saturated fat in meat that could explain why people who eat lots of red meat are at greater risk for heart disease – it may be the carnitine as well. In fact, recent research suggests that certain types of saturated fat like coconut oil may actually be beneficial by raising HDL-cholesterol levels, the kind that’s linked to a lower risk for heart disease.
What Does This Mean?
With so many other sources of protein available, it’s a good idea to limit the amount of red meat in your diet. It also wouldn’t be advisable to take carnitine supplements or drink energy drinks until more is known. Why not diversify your diet a bit by adding more fish and plant-based sources of protein to your diet?
Lentils, nuts, tempeh, and beans are good sources of protein that lack the saturated fat and carnitine that red meat has. Chicken is also low in carnitine. Four ounces of beef steak has between 56 and 162 milligrams of carnitine whereas a similar amount of chicken breast has only 3 to 5 milligrams. Eating red meat once or twice a week probably won’t greatly increase your risk for heart disease, but until more is known it’s probably best not to eat it every day. It’s also a good idea to avoid processed meat as much as possible. Fortunately, red meat isn’t the only source of protein and you can enjoy sources like chicken, fish, nuts, and legumes to avoid excessive amounts of dietary carnitine.
References:
BMC Medicine. 11:63. doi:10.1186/1741-7015-11-63.
Medical News Today. “New Link Discovered Between Heart Disease and Red Meat”
WebMD. “Vegetarian Diet May Cut Heart Disease Risk”
NIH Office of Dietary Supplements. “Carnitine”
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