Odor After Certain Foods

Your result, the one DNA position behind it, and what the research says.

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About Odor After Certain Foods

When gut bacteria break down choline and related compounds, found in eggs, fish, liver and legumes, they produce trimethylamine, which smells strongly of fish. Normally the liver enzyme FMO3 converts it into an odorless form before it reaches your breath or skin. This common variant lowers that enzyme's efficiency somewhat. In most people the reserve capacity is more than enough and nothing is noticeable; the effect, where it appears at all, is mild and tied to eating a lot of those foods at once.

Good to know: The smell comes from gut bacteria acting on food, not from the food itself. One working copy of the enzyme is normally more than enough. Any effect here is mild, temporary and tied to specific choline-rich meals.

Fun fact: Trimethylamine is the compound that makes old fish smell, formed there by bacteria breaking down a compound marine fish carry naturally, and your own gut bacteria make the same amine from choline.

Discovery: The reduced activity of this enzyme variant was characterized in 1999.

The Variant

The single variant behind this trait

Gene: FMO3

Variant (rsID): rs2266782

Location: Chr 1:171,107,825

dbSNP rs2266782

The studies

Trimethylamine N-Oxide Response to a Mixed Macronutrient Tolerance Test in a Cohort of Healthy United States Adults (James KL et al., International journal of molecular sciences, 2023)

Genetic and Nongenetic Factors Associated with Protein Abundance of Flavin-Containing Monooxygenase 3 in Human Liver (Xu M et al., The Journal of pharmacology and experimental therapeutics, 2017)

Divergence between circulating trimethylamine and trimethylamine-N-oxide associated with common flavin-containing monooxygenase 3 variation (Tang J et al., iScience, 2026)

Other lifestyle traits

Lactose Tolerance: Variants near the LCT gene that set whether you keep producing lactase, the enzyme for digesting milk, into adulthood.

Galactose Handling: A common change in GALT, the enzyme that processes galactose, half the sugar in milk. It marks a lower-activity version without settling whether you carry it.

Histamine Clearance: A change in diamine oxidase, the gut enzyme that breaks down histamine arriving in food, affecting how quickly you clear it.

Back to All Traits

Content updated September 2026.

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