Why broccoli can trigger a fishy odor in some people
Broccoli is nutritious, but in people with a rare inherited condition called trimethylaminuria, eating it can contribute to an unmistakable fish-like body odor. The condition is not an allergy and does not mean broccoli is unhealthy; it reflects how the body handles certain compounds produced during digestion.
The odor comes from a chemical the body cannot clear normally
Gut bacteria make trimethylamine, a strong-smelling compound, as they break down nutrients in food. In most people, a liver enzyme called FMO3 converts much of it into trimethylamine N-oxide, a form that has little odor and can be excreted.
In trimethylaminuria, inherited changes can leave FMO3 less able to do that job. Trimethylamine then builds up and leaves the body in sweat, breath, and urine. Foods containing nutrients that feed its production—including some cruciferous vegetables such as broccoli—can make the odor more noticeable. The effect varies from person to person; eating broccoli does not cause the genetic condition.
Why the same meal affects people differently
A person with the condition may notice the smell more after certain foods, while someone without it processes the resulting compound normally. The practical implication is that a fishy odor after eating broccoli is not, by itself, proof of trimethylaminuria: the condition is uncommon, and persistent unexplained odor warrants medical assessment rather than a broad restriction of healthy foods.
