For my previous blog entry, I wrote about the discovery of arterial plaque-buildup in the mummified remains of various ancient populations. With heart disease consistently being the leading cause of death in the United States year after year, it is clear that our relationship with our hardest-working organ has not much improved despite hundreds of years of technological and medical innovation and discovery.
But that’s not to say that progress is non-existent. Doctors and clinical researchers are working hard to uncover the roles of lifestyle, diet, and genetics in the development of heart disease. Still, there are some paradoxes that are hard to explain based on our current understanding of high-cholesterol and fatty diets promoting heart disease.
Take red meat, for example. A food that is high in protein and relatively low in fat and cholesterol. Theoretically these qualities are heart-healthy and a green light for incorporating as a staple into your diet. Why, then, is red meat the first thing to get kicked to the curb when trying to lower blood cholesterol levels? The connection to increased atherosclerosis was identified years ago, but not explained until quite recently, when researchers were able to put the blame on an unlikely source – the bacteria in our guts.
The gut microbiome is essential in the digestion of food and the proper function of our digestive system. It is a dynamic community of bacteria that changes in response to diet, disease, and antibiotic use, among many other factors. Dysfunctions of the microbiome may promote the development of Crohn’s disease or other gastrointestinal issues.
Researchers discovered that bacterial processing of L-carnitine, a molecule found in red meat, into trimethylamine-N-oxide (TMAO) caused increased cholesterol levels by slowing the removal of cholesterol from the blood stream. They confirmed their findings by observing that mice which were fed high levels of L-carnitine had double the risk of developing atherosclerosis. When the same mice were treated with antibiotics (diminishing their gut microbiome) they did not see the increased plaque deposits.
Furthermore, meat-eaters who took L-carnitine were found to have higher levels of TMAO than vegans who had the same treatment, suggesting the difference between their gut bacteria was the determining factor for TMAO levels. Meat-eaters are likely to have more L-carnitine converting bacteria simply because the consumption of meat promotes the growth of these bacteria. Vegans do not have enough of the bacteria to cause significant conversion of the L-carnitine into TMAO.
This research adds further insight towards the role of diet in the development of heart disease and opens up avenues for possible treatment or prevention plans that can hopefully put a dent in America's greatest health problem.
Koeth RA, Wang Z, Levison BS, et al. Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med. 2013;
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Posted by Joseph Starrett(3)