Eat steak, boost your risk of a heart attack

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      Red-meat lovers beware.

      That’s because Science Now has reported that new research has linked a nutrient in red meat, L-carnitine, to a higher risk of heart disease.

      L-carnitine is also added to energy drinks and energy supplements, but it comes in the highest quantities in red meat.

      According to Science Now, Cleveland cardiologist and biochemist Stanley Hazen became curious about L-carnitine after he and his colleagues published a paper in Nature on a blood compound called trimethylamine N-oxide (TMAO).

      Hazen noticed a correlation between levels of TMAO in mice and future heart-attack risk.

      He and his colleagues then reportedly devised a clever study involving feeding steak to “young, hungry students” to discover that when bacteria in the gut break down L-carnitine, it’s converted to TMAO.

      “To pin this down, they gave five of their volunteers broad-spectrum antibiotics for a week to suppress gut microbes and then repeated the experiment,” Science Now's Jennifer Couzin-Frankel reported. “This time, there was virtually no TMAO in the blood or urine after the volunteers ate steak, suggesting the conversion couldn’t happen without the bacteria present.”

      A study in Nature Medicine notes that mice fed L-carnitine for 15 weeks had far higher TMAO levels than a control group.

      “It’s still unclear why TMAO seems to promote atherosclerosis,” Science Now's Couzin-Frankel wrote. “Work by Hazen’s group hints that TMAO may make it easier for immune cells in the arteries to accumulate cholesterol.”

      Fish, chicken, and milk also have TMAO, albeit at much lower levels.

      Comments

      2 Comments

      DavidH

      Apr 9, 2013 at 9:35am

      This is just reckless scientific research. Who would deliberately feed steak to a mouse, or a "young, hungry student"?

      Pellets are fine for the former, and K.D. works great for the latter.

      Or vice versa.

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      Bob Geary

      Apr 13, 2013 at 12:43pm

      This sentence - "Fish, chicken, and milk also have TMAO, albeit at much lower levels" - is completely incorrect. You probably meant, "Fish, chicken, and milk also have CARNITINE, albeit at much lower levels."

      If carnitine were the only source of TMAO in the blood & urine, then the mistake wouldn't matter - carnitine would be a good stand-in for TMAO, since you can't have one without the other.

      But carnitine processed by a carnivore's gut bacteria is NOT the body's only source of TMAO. It's not even a very good one. Other food compounds such as choline (found in grains, dairy, eggs, poultry, fish, and beef) can also be broken down into TMAO in the body.
      And some foods already contain TMAO, so no breaking-down has to happen.

      The only natural food sources that contain significant amounts of TMAO are, in direct contradiction of your last sentence, fish.

      A 1999 study (http://www.ncbi.nlm.nih.gov/pubmed/10456680) examined the effect that 46 different foods had on urine levels of TMAO - the following is from their summary (emphasis mine):

      "Of 46 different foods investigated, ***only fish and other sea-products*** gave rise to significant increases in urinary trimethylamine and N-oxide. Ingestion of fruits, vegetables, cereal and dairy produce, and ***meats*** had no measurable effects. Reasons for the apparent lack of trimethylamine provision by foods previously thought to be precursors are given and the role of gut microflora highlighted."

      Beef (one of the 46 foods they tested on humans) did not raise or lower TMAO levels any more or less than their "control" meal did, nor any more or less than chicken, soybeans, mushrooms, pineapples, rice, apples, or plenty of others.

      Seafood, on the other hand, raised TMAO levels by as much as 100 TIMES MORE than their control meal did.

      Example: after eating a steak, volunteers excreted ~75 mmol of TMAO, which is roughly consistent with the results of this new study when the carnivores ate steak. After eating halibut, however, the volunteers excreted over EIGHT THOUSAND mmol of TMAO. If steak is bad for you because of TMAO, then seafood is literally 10,000% worse.

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