Weight Loss with Trimethylaminuria (Fish Odour Syndrome) in South Africa

Trimethylaminuria (TMAU), commonly called Fish Odour Syndrome, is a metabolic disorder in which the body cannot adequately convert trimethylamine (TMA) — a pungent, fishy-smelling compound — into its odourless form. As a result, TMA accumulates and is excreted through sweat, urine, breath, and reproductive secretions, producing a persistent fishy body odour. For many people with TMAU, the social and emotional consequences of the condition are profound — isolation, shame, anxiety, and depression are common, and these often drive emotional eating and weight gain. If you have TMAU and want to lose weight, this guide explains the biochemistry, the dietary restrictions that reduce TMA production, and how to address the emotional eating patterns that are almost universal in this condition.

What Is Trimethylaminuria?

Trimethylamine (TMA) is produced in the gut by intestinal bacteria that break down certain dietary compounds — primarily choline, lecithin (phosphatidylcholine), carnitine, and TMAO (trimethylamine N-oxide, found in marine fish). The TMA produced in the gut is absorbed into the bloodstream and transported to the liver, where the enzyme flavin-containing monooxygenase 3 (FMO3), encoded by the FMO3 gene on chromosome 1q24.3, converts TMA to TMAO (trimethylamine N-oxide) — the odourless, water-soluble form. TMAO is then excreted harmlessly in urine.

In Trimethylaminuria, mutations in both copies of the FMO3 gene reduce or abolish FMO3 enzyme activity. TMA can no longer be efficiently oxidised to TMAO. It builds up in the bloodstream and is excreted unchanged through:

• Sweat — the most socially impactful route; TMA evaporates from the skin surface and is detectable to others at extremely low concentrations
• Breath — TMA from the lungs creates the characteristic fishy breath odour
• Urine — urine has a fishy smell; TMA can be measured quantitatively in urine (ratio of TMA to TMAO) to diagnose and monitor TMAU
• Vaginal secretions — in female patients, menstruation, sexual arousal, and post-coital alkaline exposure can dramatically worsen odour

TMAU is more common than once thought — primary (genetic) TMAU from homozygous or compound heterozygous FMO3 mutations is relatively rare, but secondary TMAU — caused by increased TMA load from diet, certain gut bacteria, liver disease, or hormonal factors — is estimated to affect 1% or more of the population in some form. Women are more commonly and severely affected than men, partly because oestrogens reduce FMO3 activity and androgens enhance it.

Dietary Sources of TMA Precursors

The key insight in managing TMAU is: TMA is not a nutrient you eat directly — it is produced by gut bacteria from precursor compounds in food. Reducing TMA production requires reducing the dietary substrates that gut bacteria convert to TMA:

Choline

Choline is the most significant TMA precursor in most people's diets. Gut bacteria (including Clostridium and Erysipelotrichaceae species) convert choline to TMA via TMA lyase enzymes. Foods very high in choline include:

• Egg yolks — among the highest dietary choline sources; egg whites contain very little choline and are fine
• Liver and offal — extremely high in choline; braaiing chicken livers (a South African favourite) is high-risk for TMA production
• Kidney and other organ meats
• Full-fat milk in large quantities
• Soya beans and soya milk — moderate-high choline
• Wheat germ

Lecithin (Phosphatidylcholine)

Lecithin is a phospholipid found in many foods and used as an emulsifier in processed foods (label: E322). Lecithin is hydrolysed in the gut to release choline, which is then converted to TMA. High-lecithin foods include egg yolks, liver, and many processed foods and supplements (lecithin supplements are commonly marketed as a "health food" for brain function — avoid completely in TMAU).

Carnitine

L-carnitine is converted to TMA by gut bacteria. Carnitine is found in high concentrations in:

• Red meat — beef, lamb, and mutton (including biltong, a South African staple — unfortunately high in carnitine); the redder and fattier the meat, the more carnitine it contains
• Game meat — venison, kudu, springbok
• L-carnitine supplements — commonly marketed for weight loss; must be completely avoided in TMAU

TMAO in Marine Fish

Marine (saltwater) fish contain TMAO in their muscle tissue as an osmoprotectant. When fish dies, bacteria convert TMAO to TMA — the familiar fishy smell of aging fish. When TMAU patients eat marine fish, the TMAO is absorbed and provides a direct additional TMA load to the liver (which cannot convert it efficiently). Avoid:

• All saltwater fish — hake (South Africa's most popular fish), kingklip, tuna, yellowtail, snoek, pilchards, sardines, mackerel
• Shellfish — prawns, mussels, calamari, crab, lobster
• Fish oil supplements and cod liver oil

Freshwater fish (trout, tilapia, catfish) contain negligible TMAO and are generally tolerated, though this varies by individual.

The Emotional Eating Cycle in TMAU

This aspect of TMAU is underappreciated in medical literature but is extremely common in practice:

• Social isolation: The odour causes others to distance themselves, comment unkindly, or react visibly. Many TMAU patients describe years of social avoidance — not attending school, university, work, or social events because of the fear of causing offence. This isolation reduces physical activity (no sports, no gym, no group exercise classes).
• Shame, anxiety, and depression: These are nearly universal. Constant hypervigilance about odour — showering multiple times daily, avoiding close physical contact, monitoring other people's reactions — is exhausting and generates chronic psychological stress. Stress elevates cortisol, which promotes visceral fat accumulation and reduces satiety signalling.
• Food as a comfort: When social interaction causes pain and exercise feels too exposed, food often becomes a primary comfort and coping mechanism. The dietary restrictions of TMAU further complicate this — patients can feel trapped between foods they enjoy (biltong, braai meat, egg-based dishes) and foods that worsen symptoms.
• Perverse food-odour confusion: Some patients restrict multiple food categories beyond what is medically necessary — out of fear that any food will worsen symptoms — and end up with nutritionally incomplete diets that are simultaneously too high in calories from the allowed foods they overeat.

Addressing the emotional dimension of TMAU is as important as addressing the dietary dimension. If you recognise emotional eating patterns in yourself — eating in secret, eating in response to emotional pain rather than hunger, feeling out of control around food — speak to a clinical psychologist or counsellor. Cognitive-behavioural therapy (CBT) has good evidence for emotional eating and is available in South Africa through several channels (SADAG, the South African Depression and Anxiety Group, can provide referrals: 0800 456 789).

Safe Weight Loss with TMAU

The good news is that the core dietary restrictions for TMAU (low choline, low carnitine, avoid marine fish) are compatible with a calorie-controlled, nutrient-rich weight loss diet. The restricted foods — organ meats, egg yolks, red meat, fatty processed foods, marine seafood — are not nutritionally essential when replaced correctly. Here is what a well-planned TMAU weight loss diet looks like:

Protein Sources (Low TMA Precursor)

• Chicken breast and pork loin — significantly lower in carnitine than red meat; moderate choline but within tolerable range for most TMAU patients in normal serving sizes
• Egg whites — the yolk contains nearly all the egg's choline; egg whites are virtually choline-free and are an excellent high-protein, low-calorie food
• Freshwater fish (trout, tilapia) — low TMAO, generally well tolerated
• Low-fat dairy — yoghurt (plain, low-fat), skim milk, and low-fat cheese in moderate portions provide protein with modest choline
• Legumes in moderate portions — lentils, chickpeas, and dried beans have moderate choline but are generally tolerated in typical serving sizes and provide valuable fibre and protein

Foods to Build the Plate Around

• Non-starchy vegetables (all types — choline content in most vegetables is low to moderate and generally tolerated): broccoli, spinach, cauliflower, kale, tomatoes, peppers, onions, garlic, cabbage
• Fruit: all fruits are generally low in TMA precursors and compatible with TMAU management
• Whole grains: brown rice, oats, maize/mealie pap (a South African staple — fine for TMAU), whole wheat bread in moderate portions
• Olive oil and avocado: healthy fats with low choline and carnitine content; good for satiety

Caloric Deficit Strategy

A target deficit of 400–500 kcal/day is safe and appropriate for most adults with TMAU. Unlike many of the other rare metabolic disorders discussed on this site, TMAU does not carry a risk of metabolic crisis from caloric restriction — the primary concern is odour worsening, not acute metabolic decompensation. Practical approach:

• Eliminate all organ meats, egg yolks, marine seafood, red meat in large portions, and all L-carnitine/lecithin supplements — this simultaneously reduces TMA precursor load and removes many of the calorie-dense foods in the typical South African diet
• Replace biltong (high carnitine) with low-fat biltong alternatives made from chicken (available from some SA producers) or with egg-white-based snack proteins
• Use low-fat cooking methods (grilling, steaming, air-frying) rather than pan-frying in oil or braaiing fatty meats
• Focus on high-volume, low-calorie meals: large salads with grilled chicken or egg whites, vegetable soups, stir-fries with lean pork and vegetables over a small portion of rice

Other Management Strategies for TMAU

Beyond diet, several management approaches can reduce TMA load and improve quality of life:

• Short courses of antibiotics: Antibiotics (typically neomycin, metronidazole, or amoxicillin-clavulanate) reduce the population of TMA-producing gut bacteria, temporarily decreasing TMA production. Used in 2–3 day courses around high-stress social events (job interviews, important occasions). Discuss with your doctor — not appropriate for continuous use due to antibiotic resistance risk.
• Activated charcoal and copper chlorophyllin: These bind TMA in the gut before it is absorbed. Copper chlorophyllin (as found in some chlorophyll supplements) has evidence in TMAU and can meaningfully reduce odour. Discuss dosage with a doctor.
• pH-adjusted soaps and washes: TMA is a base (alkaline). Mildly acidic soaps and wash products (pH 5.5–6.5) help dissolve TMA from skin more effectively than standard alkaline soaps. Vitamin C (ascorbic acid) skin washes are used by some patients.
• Avoiding triggers that worsen odour: Stress (releases TMA via sweat during anxiety), physical exertion (increased sweating), and sexual activity (alkaline environments) can worsen odour transiently. Manage these rather than avoiding all activity.

Exercise and TMAU

Exercise is not metabolically dangerous in TMAU — it does not trigger metabolic crises. The challenge is social: sweating during exercise increases TMA exhalation and skin release, potentially making odour more noticeable. Practical approaches:

• Exercise alone or in private where possible — home workouts, outdoor walks in open air
• Swim in outdoor or well-ventilated pools — water dilutes surface TMA; open air disperses breath TMA rapidly
• Exercise in cooler conditions (early morning South African summer sessions) to reduce sweat volume
• Use pH-adjusted post-exercise washes immediately after any sweaty session
• Online exercise platforms and home gym equipment have expanded dramatically — TMAU is an excellent reason to invest in quality home workout options

South African Context

TMAU is underdiagnosed in South Africa. Many patients are told they have a hygiene problem or are dismissed without metabolic investigation. Diagnosis requires a urine TMA/TMAO ratio test — this is available through National Health Laboratory Service (NHLS) at some centres or via referral to a metabolic physician. The test should ideally be done after a choline challenge (eating 300 mg supplemental choline before the test) to maximise diagnostic sensitivity.

If you suspect TMAU and have not been diagnosed, ask your GP to refer you to a metabolic physician or clinical geneticist. TMAU is likely more common in South Africa than current diagnostic rates suggest, particularly given the genetic diversity of the South African population and the prevalence of certain FMO3 polymorphisms in sub-Saharan African populations.

Key Takeaways

• TMAU is caused by FMO3 gene mutations — TMA cannot be converted to odourless TMAO; it builds up and is excreted via sweat, breath, and urine.
• TMA is produced by gut bacteria from dietary choline, lecithin, carnitine, and TMAO (in marine fish).
• Core dietary restrictions: avoid egg yolks, organ meats, marine fish and shellfish, large portions of red meat and game, L-carnitine and lecithin supplements.
• Social isolation from TMAU commonly drives emotional eating and weight gain — addressing the psychological dimension is as important as dietary management.
• A 400–500 kcal/day deficit is safe; many high-calorie SA foods (biltong, braai meats, offal) also happen to be high TMA precursors, so restricting them serves both goals simultaneously.
• Egg whites, chicken breast, freshwater fish, legumes, and vegetables are the foundation of a healthy, low-TMA, calorie-controlled diet.
• Exercise is safe but should be done in private or open-air environments where sweat odour is less of a social barrier.
• Seek diagnosis via urine TMA/TMAO ratio testing if not yet confirmed.

This article is for educational purposes only and does not replace advice from your metabolic physician, dietitian, or mental health professional. If you are struggling with the emotional impact of TMAU, please seek support from SADAG (0800 456 789) or a qualified clinical psychologist.