L Carnitine is Underrated. New Meta Review Reminds Us Why. Does L carnitine cause fishy body odor? Surprising Truth and Solutions Tonum 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. CUD Deficiency Primary Carnitine Deficiency