Q & A Library

Fish odor syndrome is a rare genetic disorder that causes people to emit the smell of rotting fish. The odor can be mild or strong, but it has nothing to do with personal hygiene - the problem is an enzyme deficiency that prevents the breakdown of trimethylamine (TMA), a byproduct of protein digestion released by bacteria that live in the gut. The medical name for the condition is primary trimethylaminuria.

Normally, an enzyme called FMO3 (flavin-containing mono-oxygenase 3) takes care of TMA. But in people with fish odor syndrome, this enzyme is defective. As a result, affected individuals release TMA through their breath, sweat and urine. In some cases, the fish odor is strong and constant, but more often it comes and goes.

We don't know how common fish odor syndrome is. Extrapolating from British tests, about one percent of the population worldwide carries at least one copy of a mutated gene that is responsible for the syndrome, but you need two copies of the gene for symptoms to occur. It is estimated that worldwide incidence of the disorder itself is one in 25,000. Rates are highest in Ecuador and Papua New Guinea. The syndrome is more common in women than men; it tends to worsen around puberty, just before and during menstruation, after taking birth control pills and around menopause. To find out if you have the mutated genes, you will have to go to a lab that does genetic testing.

There is no cure, but you may be able to reduce the odor with a low protein diet that restricts the amino acid choline, found in fish, eggs, beans, and organ meats. Limiting lecithin, a common food additive that also occurs naturally in eggs, soybeans, and corn, can also help. Animal studies suggest that the compound indole-3-carbinol (I-3-C) found in broccoli and other dark green vegetables makes things worse; it further inhibits breakdown of TMA. I hate to tell anyone to avoid broccoli and greens, but you should experiment with that to see if it helps.

I would also suggest increasing your intake of water. And you might try taking a good probiotic to increase the number of friendly bacteria in your intestinal tract.

Andrew Weil, M.D.