Trimethylaminuria, or fish odour syndrome is an uncommon condition that causes an unpleasant, fishy smell. The body is unable to turn a strong smelling chemical called trimethylamine produced in the gut when L Carnitine Benefits for Male Erectile Dysfunction 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. Acetyl L carnitine is a white crystalline solid that resembles snow. It has a mild odor similar to vinegar. It is a metabolite of L carnitine, derived from the amino acid L lysine in a series IAMS PROACTIVE HEALTH Adult Healthy Dry Cat Food with Chicken, 16 Pounds Pet Supplies Plus 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.