New study links L-carnitine in red meat to heart disease

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Is red meat bad for your heart? A new study suggests it is, but not for the reasons you might expect.

There’s long been a perception—not necessarily backed by strong evidence—that eating steak, hamburger, lamb, and other red meat ups the risk of heart disease. The saturated fat and cholesterol they deliver have been cited as key culprits. A team from a half dozen U.S. medical centers says the offending ingredient is L-carnitine, a compound that is abundant in red meat.

According to this work, published online in the journal Nature Medicine, eating red meat delivers L-carnitine to bacteria that live in the human gut. These bacteria digest L-carnitine and turn it into a compound called trimethylamine-N-oxide (TMAO). In studies in mice, TMAO has been shown to cause atherosclerosis, the disease process that leads to cholesterol-clogged arteries. We know that clogged coronary arteries can lead to heart attacks.

So, case closed—don’t eat red meat? Sorry, nutritional science isn’t that simple.

“The studies of red meat and heart disease in humans are conflicting,” says Dr. Dariush Mozaffarian, associate professor of medicine at Harvard-affiliated Brigham and Women’s Hospital. “This new research was well-done and compelling, but it’s too early to decide that this molecule, TMAO, causes atherosclerosis in humans or that this is responsible for some of the associations of meat intake and risk.”

Dr. Mozaffarian, a cardiologist and epidemiologist, studies the health effects of dietary habits and other lifestyle factors in large populations. His team has previously pooled the findings of the best studies available on red meat and health and found that people who eat unprocessed red meat regularly have, at worst, only a slightly higher risk of developing heart disease. Unprocessed red meat includes virtually all fresh cuts of beef, pork, lamb, and the like.

“If you look at people who eat unprocessed red meat, there is a relatively weak association with heart disease,” Dr. Mozaffarian says. “It’s not protective—and healthier dietary choices exist—but major harms are also not seen.”

In the bigger picture, we do have pretty damning evidence about the harms of eating a particular type of meat. “Processed red meats—bacon, sausage, salami, deli meats—are associated with much higher risk of heart disease,” Dr. Mozaffarian says.

Research at the Harvard School of Public Health has shown that people who eat the most processed meats have a higher overall risk of death. The ultimate reason for this is not yet clear, says Dr. Mozaffarian, but it may be the huge doses of sodium delivered by all those low-fat deli sandwiches and salami-festooned platters.

And here comes other spoilers against the L-carnitine study: Processed meats generally contain less L-carnitine than does fresh red meat. Heart-healthy fish and chicken also contain L-carnitine, Dr. Mozaffarian points out—although five to 10 times less of it than red meat. “TMAO needs to be studied more in humans to understand the implications for public health,” Dr. Mozaffarian says. “This new research is very interesting but is not yet the final word.”

To further complicate matters, a study published online today in the Mayo Clinic Proceedings suggests that supplements of L-carnitine may help heart attack survivors reduce the chances of dying prematurely or reduce symptoms of angina (chest pain with exertion or stress).

L-carnitine supplements: “Think three times before taking”

There’s still a long way to go before we know the full story about L-carnitine and heart disease. Even so, the Nature Medicine report is very important, Mozaffarian says. It suggests that regularly eating red meat boosts the number of L-carnitine-loving bacteria in your gut. “It’s the best demonstration so far of two-way communication between ourselves and the bacteria in out gut: what we eat affects the bacteria, and what they do with what we eat can influence health.”

“Based on the Nature Medicine study, I’d be concerned about taking L-carnitine supplements,” Dr. Mozaffarian says. “There was no strong reason to take such supplements before the study, and now this well-done study suggests there may be harm. I would definitely think three times before taking an L-carnitine supplement.” The studies in the Mayo report were mostly small with short follow-up, and included only heart attack survivors.

Of course, there are reasons to avoid eating red meat that aren’t directly related to individual health. Cattle farming has devastating environmental effects, including production of greenhouse gases, water pollution, and deforestation. “Health effects in humans aside, red meat consumption is clearly bad for the health of our planet,” says Mozaffarian.


  1. Aaron

    This article was at least decent until this crap:

    “Cattle farming has devastating environmental effects, including production of greenhouse gases, water pollution, and deforestation. “Health effects in humans aside, red meat consumption is clearly bad for the health of our planet,” says Mozaffarian.”

    This is more opinion than science. Not that I’m an expert, but there have been so many studies that find contrary results. Pretty bold statement to say that red meat consumption is bad for the health of our planet.

  2. Frankie

    Question… Is this study performed with commercial beef? Meaning beef sold in your typical grocery store? I wonder what the results would be for someone whose diet is primarily organic and consumes grass fed beef with no hormones, pesticides, herbicides etc. is the bacteria from the farming process and in the meat already before it becomes part of the intestinal flora? This study is interesting but I think more specifications need to be looked at to determine if its the processing that is the true culprit. People have been eating red meat for thousands of years. The prevelance of heart disease occurs more now than in our paleo ancestors… Why?? This I think is the question that remains unanswered in scientific articles. It’s a no touch zone because the commercial farming industry would fail if the truth (although already known theoretically, yes an oxymoron I know) was proven.

  3. Kingsley

    What if the meat is well dried by smoke will it stil contian L carnitine

  4. Nalliah Thayabharan

    Meat is very environmentally unfriendly now. Large proportion of agricultural land is used to grow feed for livestock rather than food for people. In terms of food security, that’s not the greatest way to go. Livestock are also breeding grounds for disease epidemics such as various influenza strains.

  5. James Alsop

    See “Six Reasons to Eat Less Red Meat”
    Nutrition Action Health Letter June 2013
    Bottom Line: (But do study the research data therein)
    Eat as little red and processed meat as possible.
    Replace red meats with beans, lintels, soy-based veggie meats. (Love it when alternatives are recommended)
    Don’t take carnitne, lecithin, or choline supplements.

    Gasp! This person has been taking L-carnitine for years.

  6. paul

    Shocked to know that..

  7. Solmar

    So, the body builders with high blood pressure who take these supplements?

  8. Joao S. de Queiroz

    Once again, like the tobacco industry — an effort to muddle things. When are we going to learn that reductionist hypothetic- deductive studies that try to attribute a causal linkage between one factor (carnitine) and the result of a complex process (heat disease) are a waste of money. There is ample evidence world wide based on statistical associations that lead us to conclude — eating significant amounts of red meat is bad for you. We should not wait to know exactly “why” that is to change behavior —

  9. John Lerch

    It would seem to be a simple experiment to see if culturing bacteria with carnitine and various preservatives in meat might lead to greater production of TMAO

  10. Valerie

    Moderators, can you please delete my previous post on THIS article? I meant to post it on a more recent article. Sorry about that. I had two tabs open and posted on the wrong one.

    Thank you,


  11. Lisa Jackson

    Hi friends i have read lot of stuff about red meat effect on heart and found that it really lead to heat attack.

  12. Heart Fit Clinic

    This does confuse a lot of things. I think a great study that was posted in circulation March 2010 compared 3 different diets; low fat, Mediterranean diet, and low carb diet. This study showed a decreases in arterial wall thickness through carotid ultrasound and showed that diet can reverse heart disease.
    The common thread is that all these diets focused on reducing blood pressure, and decrease body weight and waist circumference. What is also mentioned that all these diets contained natural foods that are not processed.
    You can make a big difference in your heart health focusing on a diet that you can maintain long term focusing on foods that will lower inflammation and that are not processed. Nutrition containing natural foods we know works best on arterial health reducing the chance of heart attacks and strokes.

  13. Diamond Fernandes

    Interesting post. Yes the research is conflicting, however l-carnitine has been shown to improve heart health. I think the more natural the food we eat the better it is. This is evident in the case of processed vs un-processed (natural) meats). At the end of the day it is important to follow a natural diet high in natural fiber, and vegetables.

  14. Pavel

    It’s frustrating to see conflicting scientific studies. The reason I started taking the L-Carnitine with alpha-lipoic acid supplement is because the study by Bruce Ames showed that these chemicals (in combination) actually improved health in rats and increased their longevity. Having been taking the supplement on and off, I noticed a difference (and yes, I realize it might be just a placebo effect or spurious relationship). Regardless, I want to keep taking the supplement, but this news is troubling.

    I’d greatly appreciate it if somebody can answer the following though: the article says “In studies in mice, TMAO has been shown to cause atherosclerosis, the disease process that leads to cholesterol-clogged arteries. We know that clogged coronary arteries can lead to heart attacks.” Question: Do clogged arteries strongly correlate with the levels of LDL or total cholesterol? I’m an athlete with good diet habbits and (relevant) genes, so my cholesterol levels are pretty good. Does this mean that I don’t have high risk of clogging arteries or does presence of TMAO clog the arteries regardless of what the cholesterol levels are? You can see where I’m going with this.

    Thank you !

  15. Price Weston

    The human study part of this had N=6. If someone came out with a study saying supplement x had significant benefits, do you think it would get all this media attention? See the well researched paleo responses.

  16. shawn Johnson

    This study does not take into account that many vegetables raise the TMAO much higher than red meat does. Perhaps L-carnitine is not the problem.

    See this article:

    “He points out that red meat is only one of many foods that increases TMAO when eaten, and cites data from a 1999 study that evaluated TMAO excretion following consumption of 46 different foods, which shows that red meat generated no more TMAO than fruits and vegetables. In fact, some veggies, such as peas, cauliflower and carrots generated more TMAO than beef did! Still, none of the foods generated TMAO at levels that were statistically different from the control. (Similarly, there was no statistically significant difference between different kinds of meats, compared to the control.)”

  17. healthy old man

    I’ve been taking L-carnitine (as Acetyl-L-carnitine) supplements for years. At my physical earlier this month my BP was 102/62, which suggests my 69-year-old arteries aren’t being blocked. I am a vegetarian … perhaps something else in red meat is needed for carnitine to be a problem?

    • Dan Pendick

      The Nature Medicine research suggest that vegetarians may not have the mix of gut flora to convert L-carnitine into TMAO, the substance implicated in atherosclerosis. But this is only one study–albeit a very well conducted study–so it’s too early to make any conclusions about what you should and should not eat.

  18. fire proof door

    Does that mean that having L carnitine drinks can cause heart disease? I thought it helps your metabolism at pace!

    • david jackson

      Yes its raises the metabolic rate and the rate of early of death….I am no never eating red meat ever again.But isn’t carnitine in pork too?

      • Richard

        If you read the article, you’ll see they mention pork is a red meat too:
        “Unprocessed red meat includes virtually all fresh cuts of beef, pork, lamb, and the like.”

        The only people saying pork is a white meat is the pork industry.

      • Dan Pendick

        Yes, L-carnitine is in pork, and also in poultry and fish (at substantially lower levels than in red meat). Perhaps you could say “pork is the other-white-red meat.” 😉

      • fire proof door

        I guess there no safe food afterall.. sigh

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