Recent Advances in Microbiota Associated Metabolites in Heart Failure L Carnitine Tartrate SFI Health US 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 l carnitine, a friend or foe for cardiovascular disease? A Mendelian randomization study BMC Medicine Springer Nature Link