A recent article in Nature Medicine (2013) suggests that the nutrient L-carnitine, found in red meat and nutritional supplements, promotes atherosclerosis as a result of enteric bacteria in the gut forming a toxin called trimethylamine (TMA), which is further metabolized to trimethylamine-N-oxide (TMAO). Two other articles by many of the same authors similarly argue that gut bacteria transform dietary choline and phosphatidylcholine to yield TMA with negative cardiovascular consequences. Furthermore, omnivorous human subjects produce more TMAO than do vegans or vegetarians; this difference is possibly related to the higher dietary L-carnitine intake of the non-vegetarians. We argue that the conclusions from these studies relating TMO/TMAO to dietary L-carnitine, whether from food or dietary supplements, are misleading and, in fact, L-carnititne is cardioprotective.
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