Red Meat and Heart Disease: The Hidden Role of microbial L Carnitine & Choline Prof Luigi Fontana JCI l Carnitine in omnivorous diets induces an atherogenic gut microbial pathway in humans Role of carnitine in disease Nutrition & Metabolism Springer Nature Link 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