Optimizing endurance performance in elite swimmers: effects of L carnitine supplementation and hydration strategies Applied Water Science Springer Nature Link Does L Carnitine Work for Fat Loss? A Dietitian Explains Trimethylaminuria (Fish Odor Syndrome or TMAU) 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.