L Carnitine: Does it help with weight loss? Stabilizing the enzyme in fish odor syndrome 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. CUD Deficiency Primary Carnitine Deficiency 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.