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. Does L Carnitine Work for Fat Loss? A Dietitian Explains Get Rid of Fishy L Carnitine Smell: Essential Fixes Tonum Trimethylaminuria (Fish Odor Syndrome or TMAU) L Carnitine: Benefits, side effects, and dosage