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 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. Frontiers Gut Metabolite Trimethylamine N Oxide in Atherosclerosis: From Mechanism to Therapy Scientists make breakthrough in studying the enzyme involved in fish odor syndrome Trimethylamine N Oxide (TMAO) and cancer risk: Insights into a possible link ScienceDirect