Is Red Meat Dangerous?

A recent paper from the Cleveland Clinic reports more than a dozen studies that add up, say the authors, to the conclusion that red meat and other meats cause heart disease at least partly by increasing trimethylamine-N-oxide (TMAO), which is made from carnitine by intestinal bacteria. Meat, especially red meat, is high in carnitine.

The results were reported all over the world, including the New York Times. There are several reasons to question the conclusion:

1. The association between meat and heart disease is weak. An epidemiological paper from the Harvard Nurses Study found estimated reductions in heart disease on the order of 10-20% when a “healthy” food was substituted for meat. Conclusions about causality (eating Food X causes Disease Y) based on the Harvard Nurses Study have predicted wrongly over and over when tested in experiments, so even this weak association is questionable. A 2010 meta-analysis found no association between red meat consumption and heart disease. The absence of any correlation is surprising because red meat is widely believed to be unhealthy. People who eat more red meat would presumably do more other “unhealthy” things. (Perhaps the error rate of the underlying epidemiology is high. Errors push associations toward zero.)

2. Within the Cleveland paper, the associations between carnitine and TMAO and heart disease are weak. For example, people with the greatest sign of heart disease (“triple” angiographic evidence of heart disease) had only slightly more carnitine in their blood (about 15% more) than people with the least sign of heart disease. (Maybe it is peak levels of carnitine rather than average levels that matter.)

3. A 1996 epidemiological study (via Chris Kresser) that looked at the correlates of various “healthy” habits among people especially interested in health (e.g., they shop at health food stores) found no detectable effect of being a vegetarian. For example, vegetarians had the same all-cause mortality as non-vegetarians. Other factors were associated with reduced mortality, including eating wholemeal bread daily and eating fruit daily. This study looked at a large number of people (about 11,000) for a long time (17 years), so I consider the lack of difference (vegetarians versus non-vegetarians) strong evidence against the idea that modest amounts of meat are harmful.  (And I am going to start eating wholemeal bread in small amounts.)

I don’t dismiss the paper. Among people who eat more than modest amounts of meat, there may be something to it. Now and then epidemiology turns up a powerful risk factor — something associated with a risk increase by a factor of 4 or more (people at a high level of the risk factor get the disease at least four times more often than people at a low level of the factor). History shows that such correlations are likely to tell us something about causality. With weaker correlations (such as the correlation between red meat and heart disease), it is much more a guessing game.

To me, the important clue about heart disease is that it is very low in both Japan and France, much lower than in countries with high rates of heart disease. The two countries that have little in common besides the fact that in both people eat a lot more fermented food than in most places. In France, they drink wine, eat stinky cheese and yogurt. In Japan, they eat miso, pickles, and natto. Maybe fermented food protects against heart disease.

7 Replies to “Is Red Meat Dangerous?”

  1. ” … the telling fact about heart disease is that it is very low in both Japan and France, much lower than in countries with high rates of heart disease. ”


    Seth: I don’t understand your point or question.

  2. From my perspective, the authors of this study immediately lost all credibility based on their interpretation of the results from the recent Med diet trial… It was either a very disingenuous way to support their own conclusions, or they have no idea how to interpret randomized trials. I suspect it was the former. In that trial,BOTH groups were counseled to avoid red meat, so it was in no way a randomized test of the red meat hypothesis like the Cleveland Clinic authors contend.

  3. The fermented foods eaten in Japan and France also have lots of vitamin K2, which is known to help prevent heart disease.

    Of course, eating fermented foods also helps with gut flora, b vitamins and a few other benefits.

    Paul Jaminet has written a good response to that last study on TMAO.

    The major standout, to me was that once they gave the participants antibiotics, to kill their gut bacteria, and then “rebuilt” their gut flora, the TMAO levels increased *seven fold* compared to before.

    So is the problem carnitine, or disordered gut bacteria?

    The French and Japanese use less antibiotics and, from the fermented foods, have much better gut bacteria (and both eat far less “factory foods”)

    Small wonder they are much healthier.

  4. Paul N: from where do you get the idea that the French and Japanese use less antibiotics? You must not know much about those countries.

    Also, Seth, why change your diet to include wholemeal bread? whatever you’ve been doing till now appears to be working given you lowered your coronary calcium score fairly dramatically…

  5. Agreed, the association with cardio disease is weak at best. The association with colorectal cancer is much stronger, but even there, you have a lot of confounding variables (potentially) to consider: method and degree of cooking, fat content, etc. I’m not worried about the carnitine nonsense so much as I am about heterocyclic amines, on which the literature is vast. HCAs are scary.

    Japan is a country of skinny people. France not quite so much, but compared to the U.S., French are lightweights. Low BMI is the route to low CVD.

    Seth: I explain the thinness of people in Japan and France as partly due to a gourmet strain — good taste in food. They eat little “ditto food”. There are few McDonald’s in Tokyo, for example. I think this goes along with a taste for fermented food.

  6. I think that Chris Masterjohn wrote the most interesting dissection of this TMAO study here:

    Seth: I didn’t link to this discussion because I disagreed with its main points. For example, Chris says that fish has much more TMAO than meat. But since TMAO is made from the carnitine in meat, this does not mean that fish causes more TMAO inside the body than meat — which is what matters. Another example is that Chris complains that the mice experiments involved meat dosages that resembled eating 100 steaks per day. He said that was unrealistic. Because of the vast lifespan differences between mice and people, I don’t dismiss this experiment. I don’t think it is obvious what the “equivalent” number of steaks is.

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