It’s been known that eating a lot of red meat is linked to having a higher risk for a heart attack, but now new evidence in animal studies and also in humans, shows that the missing link in our understanding as to why this is so, may possibly reside in an overabundance of certain bacteria found in the guts of regular meat-eaters. Gut-microbes seem to have become the darling of our times when it comes to trying to bridge the gap in our rudimentary understanding between the foods we eat and modern diseases, and the science here still remains a big unknown.
According to research just published today in the science journal Nature Medicine, understanding why regular meat-eaters have a higher risk of heart disease is a matter of simple alchemy. A lot of previous research has shown that excessive red meat consumption is correlated to a higher risk for heart disease and hardening of the arteries through increased cholesterol deposits. Now this new study conducted in mice shows that certain intestinal microbes convert a nutrient that is found in high amounts in red meat called L-carnitine into a chemical called trimethylamine-N-oxide (TMAO); and TMAO promotes cholesterol deposition in the arterial walls and reduces the effective removal of cholesterol by the body, resulting in a high risk for heart disease. Certain carnivorous or carnitine-craving bacteria seem to grow to large colonies in the guts of meat eaters that provide them with their favorite sustenance, where they convert the nutrient L-carnitine into the cholesterol-increasing compound that is so deleterious for the heart when it is overly abundant. L-carnitine is also found in smaller amounts in other foods, such as dairy products, but red meat is by far the highest source of this amino acid.
Another study looking at vegans and meat-eaters showed that when the former ate a sirloin steak the conversion of L-carnitine into the compound TMAO that can be measured in the blood was much lower compared to regular meat-eaters, where the conversion was found to be high. This seems to provide proof for the theory that there is an association between the abundance of certain gut bacteria that use L-carnitine as a substrate and the conversion into TMAO in regular meat-eaters. “It may be that a regular diet of meat encourages higher levels of L-carnitine-TMAO converting intestinal bacteria that feed on L-carnitine that in turn increase the risk of heart disease,” according to one of the study authors.
In the accompanying news article study author Stanley Hazen, head of cardiovascular medicine at the Cleveland Clinic in Ohio, stated that the findings of the study “should give pause not only to meat lovers, but also to people who take L-carnitine supplements which are heavily marketed to promote weight loss and improve athletic performance”. In a New York Times article published today, he was quoted as saying that although not a vegan and a lover of red meat, he personally would not eat a steak more than once every 2 weeks and no more than 4 to 6 ounces at a time. His previous red meat consumption was much higher.