Did You Know? Some people report a fishy smell after supplementing with L carnitine. This happens because certain gut bacteria convert carnitine to trimethylamine, a malodorous compound found in rotting fish. Trimethylamine and Trimethylamine N Oxide, a Flavin Containing Monooxygenase 3 (FMO3) Mediated Host Microbiome Metabolic Axis Implicated in Health and Disease Drug Metabolism and Disposition Breakthrough in studying the enzyme that ultimately produces fish odour syndrome Effect of dietary fiber on trimethylamine N oxide production after beef consumption and on gut microbiota: MEATMARK a randomized cross over study European Journal of Clinical Nutrition Trimethylaminuria, or fish odour syndrome is an uncommon condition that causes an unpleasant, fishy smell. The body is unable to turn a strong smelling chemical called trimethylamine produced in the gut when JCI l Carnitine in omnivorous diets induces an atherogenic gut microbial pathway in humans