Researchers discover new link between heart disease and red meat

red meat
An uncooked rib roast. Credit: Michael C. Berch/Wikipedia

A compound abundant in red meat and added as a supplement to popular energy drinks has been found to promote atherosclerosis – or the hardening or clogging of the arteries – according to Cleveland Clinic research published online this week in the journal Nature Medicine.

The study shows that living in the metabolize the compound carnitine, turning it into trimethylamine-N-oxide (TMAO), a the researchers previously linked in a 2011 study to the promotion of atherosclerosis in humans. Further, the research finds that a diet high in carnitine promotes the growth of the bacteria that metabolize carnitine, compounding the problem by producing even more of the artery-clogging TMAO.

The research team was led by Stanley Hazen, M.D., Ph.D., Vice Chair of Translational Research for the Lerner Research Institute and section head of Preventive Cardiology & Rehabilitation in the Miller Family Heart and Vascular Institute at Cleveland Clinic, and Robert Koeth, a medical student at the Cleveland Clinic Lerner College of Medicine of Case Western Reserve University.

The study tested the carnitine and TMAO levels of omnivores, vegans and vegetarians, and examined the clinical data of 2,595 patients undergoing elective cardiac evaluations. They also examined the cardiac effects of a carnitine-enhanced diet in normal mice compared to mice with suppressed levels of gut microbes, and discovered that TMAO alters cholesterol metabolism at multiple levels, explaining how it enhances atherosclerosis.

The researchers found that increased carnitine levels in patients predicted increased risks for cardiovascular disease and major cardiac events like heart attack, stroke and death, but only in subjects with concurrently high TMAO levels. Additionally, they found specific gut microbe types in subjects associated with both plasma TMAO levels and dietary patterns, and that baseline TMAO levels were significantly lower among vegans and vegetarians than omnivores. Remarkably, vegans and vegetarians, even after consuming a large amount of carnitine, did not produce significant levels of the microbe product TMAO, whereas omnivores consuming the same amount of carnitine did.

"The bacteria living in our digestive tracts are dictated by our long-term dietary patterns," Hazen said. "A diet high in carnitine actually shifts our gut microbe composition to those that like carnitine, making meat eaters even more susceptible to forming TMAO and its artery-clogging effects. Meanwhile, vegans and vegetarians have a significantly reduced capacity to synthesize TMAO from carnitine, which may explain the cardiovascular health benefits of these diets."

Prior research has shown that a diet with frequent red meat consumption is associated with increased cardiovascular disease risk, but that the cholesterol and saturated fat content in red meat does not appear to be enough to explain the increased cardiovascular risks. This discrepancy has been attributed to genetic differences, a high salt diet that is often associated with red meat consumption, and even possibly the cooking process, among other explanations. But Hazen says this new research suggests a new connection between red meat and cardiovascular disease.

"This process is different in everyone, depending on the gut microbe metabolism of the individual," he says. "Carnitine metabolism suggests a new way to help explain why a rich in promotes atherosclerosis."

While carnitine is naturally occurring in red meats, including beef, venison, lamb, mutton, duck, and pork, it's also a dietary supplement available in pill form and a common ingredient in . With this new research in mind, Hazen cautions that more research needs to be done to examine the safety of chronic carnitine supplementation.

"Carnitine is not an essential nutrient; our body naturally produces all we need," he says. "We need to examine the safety of chronically consuming carnitine supplements as we've shown that, under some conditions, it can foster the growth of bacteria that produce TMAO and potentially clog ."

This study is the latest in a line of research by Hazen and his colleagues exploring how gut microbes can contribute to , uncovering new and unexpected pathways involved in heart disease. In a 2011 Nature study, they first discovered that people are not predisposed to cardiovascular disease solely because of their genetic make-up, but also based on how the micro-organisms in their digestive tracts metabolize lecithin, a compound with a structure similar to carnitine.

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Researchers find link between common dietary fat, intestinal microbes and heart disease

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Journal information: Nature Medicine

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Citation: Researchers discover new link between heart disease and red meat (2013, April 7) retrieved 26 August 2019 from
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User comments

Apr 07, 2013
in summary:

"Food will kill you eventually, but you need it to live."

The only meats they didn't ax here are poultry, fish, worms, shellfish, and insects.

Let's see, The American Memory Institute says Poultry is bad for the brain. Not to mention chickens and turkeys are the biggest carriers for bird flu pandemics, so your food would still be killing you.

Shellfish is bad.
Worms bad.

Insects are good.
Fish are good.

If everyone ate the recommended amount of fish the rivers, lakes, and oceans would be depleted in a year or two.

Apr 07, 2013
Seems like the answer is a highly targeted antibiotic aimed at the specific bacteria in the gut that are causing the problem.

Apr 07, 2013
@Lurker: Fish have been radioactive since Fukushima. Guess that leaves just insects. Hmmm... Fried cockroach mmm..

Apr 08, 2013
There is always Soylent Green

Apr 08, 2013
Worms bad.


Regarding all those other invertebrates, I expect that with enough applied technology, we can make anything taste at least like hamburger.

Apr 08, 2013
or stop feeding the bacteria with high-carb diets, fix the flora, and eat meat.

Apr 08, 2013
Since numerous studies have shown vegans and vegetarians live somewhat shorter lives than people who eat a well balanced diet - one has to conclude that the research only helps define what a balanced diet might mean.

Apr 08, 2013
The Masai have traditionally lived exclusively off of the meat, blood, and milk of their cattle, and they have no heart disease at all. Explain that.

Apr 09, 2013
@DavidW: sstritt is not quite as wrong as he might appear to be. I googled 'maasai diet' and came up with some pretty consistent stuff, that does appear to support his contention. Anyway, here are two of them:
The second site also gives some possible reasons why they appear to be bucking the trend despite their diet. Note that there are some key differences between them and the typical sedentary Westerner primed for his coronary; one is that they do an awful lot of moving around. Perhaps that ongoing version of 'exercise' allows the body to deal with the fat more healthily and appropriately. Even in the West, the big recommendation is for regular and frequent moderate exercise to keep the body in better shape. Not that some seem to be paying heed.
Best Regards, DH66

Apr 09, 2013

That's a lie.

We now know for a fact that humans are not designed to eat animals. We may have done it and something may be better than nothing, but the genetically proper human diet is vegan.

On the contrary, vitamin B12 is only available in our diets from meat-supplements don't count since they are a byproduct of technology. B12 is necessary for folic acid to do its work and for proper maintenance of the myelin sheath of our nerves. Only bacteria make B12, and those bacteria don't live in the right section of our gut to allow us absorb it. Hence only B12 in meat, processed by an enzyme in the stomach, is available. People without a working version of the enzyme get pernicious anemia. So do vegans who don't have access to technology, ie. supplements.

Apr 11, 2013
wow. now i don't have anything against ethical vegetarians, but to claim anything other than that humans are omnivores is just pissing against the wind. ie. stupid.

Jun 05, 2013
Humans are humans
WAIT - let me write that one down. Wow.
We are not vegetarians or carnivores or omnivores. These are actions and do not define who we are
We are what we eat. And all too often in the course of human history, we eat what we are.
Humans have developed almost no genetic changes for the digestion of flesh
Thats because we didnt need to. We were already very well adapted to eating meat.
We choke to death on it
No you choke to death on it. Dogma CAN induce palpable physiological reactions.
I bet your jaw muscles will fatigue before you manage to properly chew a piece of raw cow
Depends on what part. For instance this part is very edible on the verge of rawness:

As Ive pointed out before, meat became a prominent part of our diet when we began living in wintery climes where meat was often the only food available. See Eskimos and mongols.

Mongols conquered the world you know.

Jun 05, 2013
No they have not, or they would be dead. There are many necessary nutrients that are not in the diet you describe
The obvious example is the esquimaux who survive quite well exclusively on animal products.

"In the 1920s anthropologist Vilhjalmur Stefansson lived with and studied a group of Inuit.[40] The study focused on the fact that the Inuit's extremely low-carbohydrate diet had no adverse effects on their health, nor indeed, Stefansson's own health. Stefansson (1946) also observed that the Inuit were able to get the necessary vitamins they needed from their traditional winter diet, which did not contain any plant matter. In particular, he found that adequate vitamin C could be obtained from items in their traditional diet of raw meat such as Ringed Seal liver and whale skin (muktuk)."
They also have one of the highest infant mortality rates in the world
Well we all die. High violent death rates in the tropics are the result of overgrowth and resulting tribal conflict.

Jun 07, 2013
Chris Masterjohn thrashed this pretty thoroughly over here:


Of note is a different study which compared 8 ounces of 64 different foods against a control meal to the control meal alone. Some quotes:

"We can see that none of these foods statistically stands out from the control. Looking at the numbers alone, this "light breakfast" alone, along with carrots, cauliflower, peanuts, peas, potatoes, soybeans, and tomatoes generated more trimethylamine and TMAO than beef."

"Here we see that, unlike beef, all the invertebrate seafoods tested except cockles produced statistically significantly more TMAO than the "light breakfast" control alone. Based on my own statistical test, all of the seafoods shown in the graph except clams and cockles produced significantly more TMAO than beef."

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