L carnitine is primarily synthesized in the liver from the amino acids lysine and methionine through a series of four enzymatic reactions, with the liver and kidneys converting the precursor butyrobetaine into active TMAO: The Gut Metabolite Linking Red Meat to Cardiovascular Disease Carnitine Deficiency: What Is It, Causes, Symptoms, and More Osmosis Cardiovascular Disease Linus Pauling Institute Oregon State University