Frontiers The effect of L carnitine supplementation on lipid profile in adults: an umbrella meta analysis on interventional meta analyses 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 Linus Pauling Institute Oregon State University L Carnitine Linus Pauling Institute Oregon State University