Can Eating Fish Cause You to Smell Like Fish? Understanding Trimethylaminuria (TMAU)

January 2, 2026 •

3 min read

Approximately 1 in 200,000 to 1 million people worldwide have a rare metabolic disorder called trimethylaminuria (TMAU), which is the primary reason why eating fish can cause you to smell like fish. This condition, also known as fish odor syndrome, is a genetic disorder that affects the body's ability to process a specific chemical.

Quick Summary

This article explores the rare genetic disorder Trimethylaminuria (TMAU), explaining how a faulty FMO3 enzyme prevents the breakdown of a smelly chemical called trimethylamine (TMA). It details the metabolic process, trigger foods, and management strategies for those affected by the condition.

Key Points

Rare Genetic Condition: The primary cause for a fishy body odor after eating fish is a rare metabolic disorder called Trimethylaminuria (TMAU).
FMO3 Enzyme Deficiency: TMAU is caused by a faulty FMO3 enzyme, which prevents the body from breaking down the smelly compound trimethylamine (TMA).
Dietary Triggers: Foods high in choline and carnitine, including seafood, eggs, and beans, can exacerbate the odor in individuals with TMAU.
Release via Body Fluids: The excess TMA builds up in the body and is released through sweat, breath, and urine.
Management Strategies: Symptoms can be managed through dietary restrictions, using low pH soaps, and sometimes with supplements like riboflavin or antibiotics.

What is Trimethylaminuria (TMAU)?

Trimethylaminuria, often called fish odor syndrome, is a rare genetic metabolic disorder characterized by a fishy body odor, which can also present as a scent similar to garbage or stale urine. The smell is not due to poor hygiene but results from the body's inability to break down a specific compound called trimethylamine (TMA). This chemical, responsible for the smell of rotting fish, then builds up in the body and is released through sweat, breath, urine, and other bodily fluids.

The Role of the FMO3 Enzyme

At the heart of TMAU is a genetic defect in the flavin-containing monooxygenase 3 (FMO3) gene. This gene provides instructions for creating the FMO3 enzyme, primarily active in the liver. The enzyme's job is to convert foul-smelling trimethylamine (TMA) into the odorless trimethylamine N-oxide (TMAO). In individuals with primary TMAU, a genetic mutation causes a deficiency or total absence of the FMO3 enzyme, disrupting this metabolic process.

The Metabolic Pathway of TMA

For most people, the ingestion of food containing choline and carnitine, which are found in fish, eggs, beans, and certain meats, leads to gut bacteria producing TMA. The healthy FMO3 enzyme in the liver then quickly and efficiently converts this TMA to TMAO, which is excreted harmlessly. However, when the enzyme is faulty, the body is overwhelmed, and the excess, stinky TMA is released via bodily secretions instead. Deep-sea fish, in particular, contain naturally high levels of TMAO to help them cope with high-pressure environments, which is then converted to TMA by gut bacteria and can exacerbate symptoms in people with TMAU.

Dietary and Lifestyle Triggers

While the underlying cause of TMAU is genetic, dietary and lifestyle factors can significantly affect the intensity of the odor.

Foods that can exacerbate TMAU symptoms include:

Seafood and Shellfish: Particularly deep-sea species.
Eggs: Specifically the yolk, which is high in choline.
Legumes: Such as beans, peanuts, and peas.
Offal: Liver and kidney.
Milk: From certain cows.
Brassica vegetables: Broccoli, cabbage, and cauliflower.
Supplements: High doses of choline, lecithin, and carnitine can overload the system.

Non-dietary triggers include:

Stress: Can increase sweating and worsen odor.
Exercise: Strenuous activity that increases sweating.
Hormonal Changes: Women may experience more pronounced symptoms during menstruation, puberty, or menopause.

Managing the Condition

There is currently no cure for TMAU, but symptoms can be effectively managed with lifestyle and dietary adjustments.

Dietary Management

Working with a specialist dietitian is crucial for creating a meal plan that reduces TMA-precursors without causing nutritional deficiencies. A key part of management is limiting the intake of high-choline foods, particularly seafood and eggs.

Hygiene Practices

Maintaining good personal hygiene is important for managing symptoms, but it won't resolve the underlying issue. Using slightly acidic soaps or body washes (pH 5.5-6.5) can help neutralize the alkaline TMA on the skin and reduce the smell.

Medical Interventions

Antibiotics: Short courses of specific antibiotics can reduce the amount of TMA-producing bacteria in the gut.
Supplements: Your doctor may recommend supplements like riboflavin (Vitamin B2), which can help enhance any residual FMO3 enzyme activity, or activated charcoal, which can bind to TMA in the gut and aid in its removal.

Comparison: TMAU vs. Normal Metabolism


Feature	Normal Metabolism	Trimethylaminuria (TMAU)
FMO3 Enzyme	Fully functional and efficient	Deficient or non-functional due to genetic mutation
TMA Breakdown	Converts smelly Trimethylamine (TMA) to odorless Trimethylamine N-oxide (TMAO)	Unable to convert TMA, leading to its accumulation
Fish Consumption	No lasting body odor caused by fish; TMAO is processed efficiently	Can trigger a strong, pervasive fishy odor
Excretion	TMAO is excreted harmlessly in urine	Excess TMA is released through sweat, breath, and urine

Conclusion

While eating fish will not cause a lasting, pervasive fishy body odor for most people, it can for those with the rare metabolic disorder Trimethylaminuria (TMAU). The condition is caused by a genetic deficiency in the FMO3 enzyme, which impairs the body's ability to break down the compound trimethylamine. Management focuses on dietary adjustments to reduce intake of high-choline foods, maintaining proper hygiene, and potentially medical interventions like antibiotics or supplements. If you suspect you have TMAU, it is important to consult a healthcare professional for a proper diagnosis and treatment plan to manage the condition's social and psychological effects.

For more detailed information on the genetic aspects of this disorder, see the National Center for Biotechnology Information's resource on the FMO3 gene: FMO3 gene - MedlinePlus.

Frequently Asked Questions

The main reason is a rare genetic disorder called trimethylaminuria (TMAU). It prevents the body from properly processing the chemical trimethylamine (TMA), which is found in some foods.

The FMO3 enzyme is a liver enzyme that typically breaks down smelly trimethylamine (TMA) into odorless trimethylamine N-oxide (TMAO). In TMAU, this enzyme is deficient or non-functional.

People with TMAU should limit or avoid foods high in choline and carnitine, such as seafood, eggs, beans, certain meats, and brassica vegetables like broccoli.

There is no cure for TMAU, but the symptoms can be managed. Treatment options include dietary modifications, using specific hygiene products, and, in some cases, medication.

Yes, high doses of supplements containing choline or carnitine can cause temporary symptoms similar to TMAU by overwhelming the body's processing capacity.

TMAU is diagnosed by measuring the levels of trimethylamine in a person's urine. Genetic testing can also determine if the condition is inherited.

The condition itself is not associated with other physical health problems. However, the strong odor can cause significant social and psychological distress, including anxiety and depression.