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 Carnitine: Genetic Variants Affecting Mitochondrial Energy and Health Comparison of short term and long term effects of peroral L carnitine intake: clinical implications of elevated TMAO levels in cardiovascular complications