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Approved as a "natural health supplement" in the USA and Canada, L-carnitine has been long recommended for for heart protection in people who have already had heart attacks. But a recent study suggests that L-carnitine worsens atherosclerosis. Does it?

The reason for the difference, the scientists believe, is that vegans don't have Acinebacter in large numbers in their colons, so their bodies don't receive toxic TMAO from their food. The researchers also note that mice given antibiotics to kill gut bacteria likewise don't have dangerous levels of TMAO in their blood.

But the analysis doesn't support the idea that certain foods, like red meat, are the real source of artery-clogging TMAO. In fact, many plant foods and most seafoods cause the body to release far more TMAO than red meat.

The Truly "Toxic" Foods May Surprise You

Scientists have found that servings of certain foods cause the creation of less than 100 mM (a chemical measurement) of TMAO in the eight hours after the meal. These include:

  • Oranges,
  • Apples,
  • Pineapples,
  • Pears.
  • Soybean products, and
  • Beef, beef leading to lower levels of TMAO than soy.

Servings some of certain other foods cause the creation of more than 100 mM but less than 200 mM of TMAO in the eight hours after the meal. These foods include:

  • Mushrooms,
  • Eggs,
  • Cheese,
  • Peas,
  • Cauliflower, and
  • (Irish or white) potatoes.

In other words, eating 3-1/2 ounces (100 grams) of cauliflower releases more of the artery-clogging TMAO than eating 3-1/2 ounces (100 grams) of rib eye steak.

An ovo-lacto vegetarian diet is, by this measure, more harmful than a diet including red meat.

But there are other foods that cause the release of even more TMAO.

  • Eating a 3-1/2 ounce (100 gram) serving of squid leads to the formation of over 6000 mM of TMAO.
  • Eating the same sized serving of skate leads to the formation of over 5000 mM of TMAO.
  • Eating the same sized serving of prawns leads to the formation of over 4000 mM of TMAO.
  • Eating the equivalent serving of crab leads to the formation of over 2000 mM of TMAO.
Certain sea foods are over 80 times more "toxic" than pork, more than 100 times more toxic than beef, more than 120 times more toxic than chicken, and more than 500 times more toxic than duck. And most common vegetables are more toxic than any of the meats listed in this paragraph.

But that isn't all that the headline stories leave out.

Even in Vegans, the Body Can Make TMAO

Even in vegans, the body makes L-carnitine. The authors of the study use that fact to point out (the references to figures are in the original article) that:

"In most subjects examined, despite clear increases in plasma d3-carnitine and d3-TMAO concentrations over time (Fig. 1e), post-prandial changes in endogenous (unlabeled) carnitine and TMAO concentrations were modest (Supplementary Fig. 5), consistent with total body pools of carnitine and TMAO that are relatively very large in relation to the amounts of carnitine ingested and TMAO produced from the carnitine challenge."

In plain language, a vegan eating steak experienced only about half the rise in TMAO as an omnivore eating steak, and the total rise in TMAO was very, very small, most of it coming from the fact that the steak was served with vegetables.

And the study's authors failed to address the previously established fact that more L-carnitine is converted to TMAO in the presence of estrogen. That is, foods that are high in L-carnitine, which is really sea foods and certain veggies, produce more of the artery-clogging chemical TMAO in women than in men.

The recent headlines about the toxic effects of red meat seem to  be greatly overstated. If you choose not to eat meat because you respect animals, good for you. But don't refuse lean red meat because it's not good for your heart. Take a closer look at calamari, instead.

  • Koeth RA, Wang Z, Levison BS, Buffa JA, Org E Sheehy BT, Britt EB, Fu X, Wu Y, Li L, Smith JD, Didonato JA, Chen J, Li H, Wu GD, Lewis JD, Warrier M, Brown JM, Krauss RM, Tang WH, Bushman FD, Lusis AJ, Hazen SL. Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med. 2013, April 7 [Eub ahead of print].
  • Mendelsohn AR, Larrick J. Dietary modification of the microbiome affects risk for cardiovascular disease. Rejuvenation Res. 2013 May 8.
  • Photo courtesy of Óscar by Flickr : www.flickr.com/photos/ocreactive/3025556205/
  • Photo courtesy of IwateBuddy by Flickr : www.flickr.com/photos/brucewood/535612522/

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