Health issues
Studies published in 2013 indicate that high levels of TMAO in the blood are associated with an increased risk of major adverse cardiovascular events.[9] The concentration of TMAO in the blood increases after consuming foods containing carnitine[10] or lecithin[9] if the bacteria that convert those substances to TMAO are present in the gut.[11] High concentrations of carnitine are found in red meat, some energy drinks, and some dietary supplements; lecithin is found in soy, eggs,[11] as an ingredient in processed food and is sold as a dietary supplement. Some types of normal gut bacteria (e.g. species of Acinetobacter) in the human microbiome convert dietary carnitine to TMAO. TMAO alters cholesterol metabolism in the intestines, in the liver, and in artery wall. In the presence of TMAO, there is increased deposition of cholesterol in, and decreased removal of cholesterol from, peripheral cells such as those in the artery wall.[12]
The link between cardiovascular diseases and TMAO is disputed by other researchers.[13] Clouatre et al. argue that choline sources and dietary L-carnitine do not contribute to a significant elevation of blood TMAO, and the main TMAO source in the diet is fish.[14]
Another source of TMAO is dietary phosphatidylcholine, again by way of bacterial action in the gut. Phosphatidyl choline is present at high concentration in egg yolks and some meats.
It has been suggested that TMAO may be involved in the regulation of arterial blood pressure and etiology of hypertension[15] and thrombosis (blood clots) in atherosclerotic disease.[16]