Carnitine Deficiency: What Is It, Causes, Symptoms, and More Osmosis Lets talk about L Carnitine, If youre in the gym community, youve probably heard of L Carnitine but what actually is it?, L Carnitine is a naturally occurring compound that plays a role in helping 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. Carnitine: the claims and why it may not work L carnitine supplements can cause a fishy odor in the breath, sweat, and urine. This is likely due to the formation of trimethylamine (TMA). TMA is also responsible for the pungent smell of