Carnitine Deficiency: What Is It, Causes, Symptoms, and More Osmosis A recurring fishy odor could indicate a larger medical problem. 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 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.