Frontiers Trimethylamine N Oxide Pathway: A Potential Target for the Treatment of MAFLD Trimethylaminuria (Fish Odor Syndrome or TMAU) 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 Carnitine Deficiency: What Is It, Causes, Symptoms, and More Osmosis