The gut bacteria that produce trimethylamine (the fishy-odor compound) — why some people smell worse than others, and what to do about it.

TMA and TMAO: Why Your Body Produces Trimethylamine (and What It Means for Gut Health)

Meta:

Category: Microbiome
Author: ImproveGutHealth Team
Date: July 7, 2026
Read Time: 7 min
Tags: [TMA, TMAO, Trimethylamine, Body Odor, Fish Odor Syndrome, Cardiovascular, Microbiome, Choline]

Disclaimer

This content is for informational purposes only and is not medical advice. It is not a substitute for professional diagnosis or treatment. Strong or persistent body odor changes should be discussed with a clinician — primary trimethylaminuria is a rare genetic condition that requires specialist evaluation.

The quick answer

Trimethylamine (TMA) is produced by certain gut bacteria when they break down choline, carnitine, and lecithin (from foods like eggs, red meat, fish, and some legumes). Most people have liver enzymes (FMO3) that convert TMA to odorless TMAO and excrete it. But when:

Gut bacteria over-produce TMA
FMO3 enzyme activity is reduced
The liver is overloaded

...then TMA accumulates and gets excreted in sweat, breath, and urine — causing fishy body odor or "fish odor syndrome." TMAO levels in blood are also linked to cardiovascular disease risk.

Three situations commonly produce elevated TMA/TMAO:

High-choline, high-carnitine diet without enough fiber to keep the responsible bacteria in check
Dysbiosis — overgrowth of TMA-producing species (especially with low fiber)
Genetic FMO3 deficiency (primary trimethylaminuria, rare but real)

The mechanism: gut bacteria + liver chemistry

The pathway:

You eat foods containing choline, carnitine, betaine, or lecithin
Specific gut bacteria (notably Prevotella, some Bilophila, Desulfovibrio, and others) produce an enzyme called TMA-lyase
TMA-lyase cleaves those nutrients into trimethylamine (TMA) — volatile, fishy-smelling
In healthy people, FMO3 (flavin-containing monooxygenase 3) in the liver oxidizes TMA → TMAO
TMAO is excreted in urine (odorless)

When this pathway is off:

High TMA production (TMA-producing bacteria blooming) → fishy odor in sweat/breath/urine
Low FMO3 activity (genetic, enzyme-suppressing medications, liver stress) → TMA accumulates
High blood TMAO (recently emerging as a cardiovascular risk marker)

Why this matters for gut health

Three big reasons this is more than just about smell:

1. TMAO as a cardiovascular risk marker

Multiple large studies (Cleveland Clinic research, etc.) have linked elevated blood TMAO to increased risk of heart attack, stroke, and cardiovascular death. The mechanism is debated — TMAO may promote atherosclerosis, alter platelet function, and affect bile acid metabolism.

Important nuance: TMAO from diet isn't the same as TMAO from gut overproduction. Eating fish (high TMAO itself) is associated with lower cardiovascular risk. The carnitine/choline → gut bacteria → TMA → liver TMAO pathway is the concerning one.

2. Dysbiosis indicator

High TMA producers bloom when:

Fiber intake is chronically low
Protein (especially red meat) dominates the diet
Choline/carnitine intake is high without plant diversity
The gut lacks the bacteria that prefer fiber fermentation

If your TMA production is elevated, your gut community is signaling dysbiosis.

3. The fishy odor signal

For people who experience body odor changes after antibiotic courses, during high-protein diets, or with chronic digestive symptoms, TMA-elevation is often a piece of the puzzle.

Three scenarios that produce elevated TMA/TMAO

Scenario 1: High animal-product, low-fiber diet

The classic pattern. Lots of eggs, red meat, and minimal plant diversity = lots of TMA substrate + lots of TMA-producing bacteria. Reducing animal products and adding 30+ plant foods per week usually normalizes this within weeks.

Scenario 2: Post-antibiotic dysbiosis

Antibiotics can wipe out the bacteria that prefer fiber fermentation, leaving TMA-producers to bloom. After a course of antibiotics, you may notice changes in body odor for weeks. Recovery of fiber-fermenting species with prebiotics + diverse diet restores balance.

See gut recovery timeline.

Scenario 3: Primary trimethylaminuria (rare)

Some people carry FMO3 gene variants that significantly reduce enzyme activity. They produce fishy body odor from childhood, independent of diet. Diagnosis requires specialist evaluation (urine TMA testing, sometimes genetic testing). Management includes low-choline/carnitine diet, antibiotic protocols to reduce gut TMA producers, and riboflavin + FMO3 cofactor support.

If the odor pattern is severe and persistent regardless of diet, see a metabolic specialist.

What to do about elevated TMA

Diet-level changes

Reduce choline/carnitine-rich foods if heavily consumed: red meat, eggs (2/day → 1/day), liver, some fish
Increase fiber dramatically — 30+ plant foods per week, especially leafy greens, legumes, whole grains
Prebiotic foods: oats, garlic, onion, asparagus, bananas (these feed fiber-fermenters and crowd out TMA-producers)
Choline is essential — don't eliminate entirely (needed for liver, brain function). Just balance with plant diversity.

Probiotic and microbiome support

Avoid L-carnitine supplements and excessive choline supplements
Strain-specific probiotics: Lactobacillus rhamnosus GG, Bifidobacterium longum (some evidence for shifting TMA production balance)
Prebiotic supplementation: PHGG, inulin (in moderation — can flare in sensitive people)

Medications to be aware of

Some medications suppress FMO3:

Certain antidepressants (SSRIs, especially)
Tagamet / cimetidine (H2 blocker)
Some antibiotics (especially metronidazole)
Some antifungals

If you're on a medication that affects FMO3 and notice fishy odor, discuss with your prescriber.

Testing

Urine TMA test (after choline load): clinical testing for trimethylaminuria
Blood TMAO: emerging cardiovascular risk marker; Cleveland Clinic and other specialty labs offer it
Stool microbiome testing — if dysbiosis is the suspected driver

The cardiovascular question

Multiple observational studies link blood TMAO to cardiovascular events. Some cardiologists now include TMAO in cardiovascular risk panels.

Current interpretation:

Elevated TMAO from gut bacterial overproduction (low-fiber, dysbiosis-prone diet) → probably worth addressing
Elevated TMAO from eating fish (which contains TMAO directly) → associated with lower CV risk, neutral or positive
Genetic FMO3 variants → moderate CV risk elevation, manageable

If your TMAO is elevated, optimizing fiber intake + reducing processed red meat is the primary intervention. Adding fish as a protein source can be protective.

The good news

For most people with mild TMA-elevation, simple interventions work:

Increase fiber: this is the single biggest lever
Diversify the diet: 30+ plants per week
Reduce red meat: 2-3 servings/week instead of daily
Avoid L-carnitine supplements unless medically needed
Probiotics and prebiotics: support fiber-fermenting species

Most people see normal TMA/TMAO within 4–8 weeks of these changes. Body odor changes resolve in days to weeks.

The bottom line

TMA and TMAO are real biomarkers and real gut health signals. For most people, elevated TMA reflects a fiber-deficient, dysbiosis-prone diet. Fixing fiber intake and diversifying the diet is the primary intervention. If you experience persistent fishy body odor independent of diet, see a metabolic specialist for primary trimethylaminuria evaluation. If your cardiovascular risk workup includes elevated TMAO, addressing gut dysbiosis through diet + lifestyle often normalizes it.