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. 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 N Oxide in Aquatic Foods Journal of Agricultural and Food Chemistry Stabilizing the enzyme in fish odor syndrome Carnitine Deficiency: What Is It, Causes, Symptoms, and More Osmosis Trimethylaminuria: FMO3 mutations that cause malodorous body odor