Carnitine: Genetic Variants Affecting Mitochondrial Energy and Health Does L carnitine cause fishy body odor? Surprising Truth and Solutions Tonum L Carnitine: Everything You Need to Know 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. If you are like a lot of people, you may have never heard of carnitine but this important nutrient is critical for our body's ability to optimally burn fat required for energy.