Anyone hear the recent findings the it’s the carnitine in red meat that causes heart disease rather than the saturated fat or cholesterol? They say that bacteria in our gut convert the carnitine to a substance called TMAO which causes heart disease. A little concerning for me being a big red meat eater. Anyone have any input on this?
Doctors have long assumed that saturated fat and cholesterol in red meat are what raise the risk of heart disease. But a study in the journal Nature Medicine fingers another culprit: carnitine, a compound abundant in red meat that also is sold as a dietary supplement and found in some energy drinks.
Health reporter Melinda Beck points out a compound found in red meat, energy drinks and several other foods has been found to raise the risk of heart disease. Photo: Getty Images.
Carnitine typically helps the body transport fatty acids into cells to be used as energy. But researchers at the Cleveland Clinic found that in both humans and mice, certain bacteria in the digestive tract convert carnitine to another metabolite, called TMAO, that promotes atherosclerosis, or a thickening of the arteries.
The researchers, led by Stanley Hazen, chief of cellular and molecular medicine at the Cleveland Clinic’s Lerner Research Institute, tested the carnitine and TMAO levels of omnivores, vegans and vegetarians, and examined records of 2,595 patients undergoing cardiac evaluations. In patients with high TMAO levels, the more carnitine in their blood, the more likely they were to develop cardiovascular disease, heart attacks, stroke and death.
Many studies have linked consumption of red and processed meat to cardiovascular disease and some cancers. The Harvard School of Public Health reported last year that among 83,000 nurses and 37,000 male health professionals followed since the 1980s, those who consumed the highest levels of red meat had the highest risk of death during the study, and that one additional serving a day of red meat raised the risk of death by 13%.
The new findings don’t mean that red meat is more hazardous than previously thought. But they may help explain the underlying risk of eating red meat, which some researchers have long thought was higher than the saturated fat and cholesterol content alone could explain.
Dr. Hazen speculated that carnitine could be compounding the danger. “Cholesterol is still needed to clog the arteries, but TMAO changes how cholesterol is metabolized?like the dimmer on a light switch,” he said. “It may explain why two people can have the same LDL level [a measure of one type of cholesterol], but one develops cardiovascular disease and the other doesn’t.”
One surprising finding, Dr. Hazen said, was how a long-term diet that includes meat affected the amount of TMAO-producing bacteria in the gut and thus magnified the risk. In the study, when longtime meat-eaters consumed an eight-ounce steak and a carnitine supplement, their bacteria and TMAO levels rose considerably. But when a vegan ate the same combination, he showed no increase in TMAO or bacterial change.
“Vegans basically lose their ability to digest carnitine,” said Dr. Hazen.
The study, sponsored by the National Institutes of Health, didn’t assess how little red meat people could consume and still have elevated TMAO. Nor did it look at how long someone had to abstain from red meat to end the process. “We know it will be longer than one week, but shorter than one year,” Dr. Hazen said.
He and his colleagues have been exploring how altering gut bacteria might influence the risk of heart disease. “In the future, maybe there will be a heart-healthy yogurt, or a drug to block the formation of TMAO,” he said.
Consumption of red meat?primarily beef, veal, lamb and pork?has been falling gradually since 1970.
Trade groups for meat producers have questioned the link to cardiovascular disease, saying studies that ask people to recall what they ate over long periods are imprecise.
“Cardiovascular disease?is a complex condition that appears to have a variety of factors associated with it, from genetics to lifestyle,” said Betsy Booren, chief scientist at the American Meat Institute Foundation.
As a dietary supplement, carnitine is designated as “generally regarded as safe” by the Food and Drug Administration, but few studies have looked at its long-term safety. A 2006 risk assessment found no adverse effects when subjects consumed 2,000 milligrams a day for six months. (An eight-ounce steak has roughly 200 mg of carnitine.)
Ads for supplements promote carnitine as helping boost energy levels, particularly in endurance sports, and assisting in recovery after intense exercise; some also claim that it helps shed pounds and improve brain function.
Duffy MacKay, vice president for scientific and regulatory affairs at the Council for Responsible Nutrition, a trade group for the supplement and energy-drink industries, called the study “a new, emerging hypothesis,” but said the researchers were drawing large conclusions from small studies of mice, bacteria and human biomarkers. “The concept that one component of your diet, or one molecule, is responsible for your health woes is questionable,” he said.
Dr. Hazen noted that some energy drinks have more carnitine in a single can than a porterhouse steak. “I worry about what happens in 10, 20 or 30 years of consumption,” he said.
He said humans generally have plenty of carnitine in their diet, which also is found in small amounts in nuts, beans, vegetables and fruit, and don’t need to take it in supplement form.
Man this is an eye opener,thanks Dr.P.I supplement with carnitine and eat meat of course so i’m going to drop the supplement side of this at least.
Yes Dr. P that’s exactly the reports I had read. My question is what types of bacterial gut bacteria are they talking about? Is it as simple as good vs bad and just supplementing with pro and prebiotics? Is there a way to stop the conversion of carnitine to TMAO?
While I’d like to see what bacteria are specifically implicated in this, as far as I know various members of the Enterobacteriaceae family (a group famous for its strict/opportunistic pathogens but also comprised of numerous commensal organisms) can make use of dietary carnitine as an electron donor.
They usually mind their own business until they get a chance to sucker punch us (unless you get shafted with food poisoning or something), which is typically in states of inflammation where they are seen to be able to capitalize on the inverse relationship they have with the obligate anaerobes associated with health.
As far as using probiotics to inhibit this conversion… well, it never hurts to take care of your gut, but my guess is these guys won’t REALLY be going anywhere unless you already have a genuine imbalance going on. I couldn’t access the article, but from the abstract it looks like the only thing they did to modulate GI flora was suppress it. Which is good enough for their experiment, but I guess not enough for the rest of us who just want to eat a burger in peace.
Red meat is associated with heart disease in about as many studies as show that it’s inversely associated.
There is little to no evidence linking saturated fat and heart disease.
Hell, even note in this article that red meat consumption has been decreasing since 1970 while instance of heart disease has been exploding.
Hmm this is interesting, considering I have been taking supplementary carnitine for quite some time (and now take it through Brain Candy). My question is would there be any difference between L-carnitine-tartrate and Acetyl-L-Carnitine Propionate? My guess is no.
This is ridiculous. There are literally thousands of studies showing the health benefits of carnitine. But people stir up a storm when one negative study comes out (and obviously is published in the media).
IMO, there is clearly much more to this. There’s nothing to be said about the specificity of the intestinal bacteria - how do we know that it’s not a pathogenic bacteria and not something that is present in healthy individuals?
Furthermore, the entire human genome evolved on eating meat. Some cultures have had incredibly high meat consumption. But somehow we’ve made it to today eating meat.
Something about this just doesn’t add up.