Does L carnitine cause fishy body odor? Surprising Truth and Solutions Tonum A recurring fishy odor could indicate a larger medical problem. Microbiota and MalodorEtiology and Management Acetyl L carnitine erectile dysfunction: What the evidence and real world use actually show 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.