Does Carnitine Cause Body Odor? Lume Deodorant 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 always smell sweaty, sour, or like onions, you need to check your gut because most body odor starts inside; constipation, yeast overgrowth, and poor bile flow create toxic sweat, so L carnitine: Health Benefits, Side Effects, Uses, Dose & Precautions 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.