Understanding Trimethylaminuria: The Root of the Fishy Odor
The phenomenon of a fishy body odor resulting from supplements is primarily linked to a metabolic condition called trimethylaminuria (TMAU), also known as "fish odor syndrome". In a healthy body, the liver produces an enzyme called flavin-containing monooxygenase 3 (FMO3), which breaks down the pungent chemical trimethylamine (TMA) into an odorless compound. TMA is produced by gut bacteria when they digest certain nutrients from food and supplements. If the FMO3 enzyme is non-functional or overwhelmed, TMA builds up and is released through sweat, breath, and urine, causing a distinctive, unpleasant fishy smell.
TMAU exists in two main forms. Primary TMAU is a genetic disorder caused by a mutation in the FMO3 gene, leading to a congenital deficiency of the enzyme. In contrast, secondary TMAU is an acquired or temporary form that can be triggered by factors like excessive intake of TMA-precursor compounds—often through high-dose supplements. Liver or kidney disease can also cause secondary TMAU by interfering with TMA clearance.
The Main culprits: Supplements That Can Trigger a Fishy Scent
Several supplements are known to increase the body's TMA load, potentially causing or exacerbating a fishy body odor, especially at high doses or in susceptible individuals. These are typically compounds that are precursors to TMA and are broken down by gut bacteria.
Choline Supplements
Choline is an essential nutrient vital for liver function, brain development, and nerve activity. However, it is also one of the most significant dietary sources of TMA precursors. When taken in high-dose supplements, particularly exceeding the recommended daily intake of 550 mg for men and 425 mg for women, choline can overwhelm the liver's capacity to process TMA. The excess choline is then converted by gut bacteria into TMA, leading to a fishy odor. The upper tolerable intake level for adults is 3.5 grams per day, and exceeding this significantly increases the risk of side effects, including the fishy smell.
Carnitine Supplements
L-carnitine is a compound derived from amino acids that plays a critical role in energy production by transporting fatty acids into the mitochondria. It is a popular supplement among athletes and bodybuilders. Like choline, carnitine serves as a precursor to TMA, and high doses can lead to the production of excess TMA by gut microbiota. Oral doses of 3 grams or more per day are specifically noted to cause side effects such as nausea, diarrhea, and a fishy body odor. The odor is often resolved by reducing or stopping the supplement intake.
Fish Oil and Lecithin
Fish oil supplements are a common source of omega-3 fatty acids, often containing trimethylamine N-oxide (TMAO) or lecithin, another choline source. In the gut, TMAO can be converted to TMA, and lecithin is metabolized into choline, both of which can contribute to the unpleasant smell. While high-quality, fresh fish oil is less likely to cause this issue, rancid fish oil is more prone to producing a fishy odor. In individuals with TMAU, or those sensitive to TMA precursors, lecithin-containing supplements should be avoided.
Betaine
Betaine is another compound that, like choline, acts as a methyl-group donor in the body. While lower, dietary levels are not generally a concern, excessive intake through supplements has been associated with fishy body odor symptoms. Large doses of 12 grams per day or more have been known to cause issues, similar to other TMA precursors.
Comparison of Key Supplements Causing Fishy Odor
| Supplement | Primary Mechanism | Typical Triggering Dose | Underlying Condition | Management Strategy |
|---|---|---|---|---|
| Choline | Gut bacteria metabolize excess choline into TMA. | >3.5 grams/day (high doses) | Primary TMAU, secondary (high-dose) TMAU | Reduce dose, avoid high-choline foods |
| L-Carnitine | Gut bacteria convert carnitine into TMA. | >3 grams/day | Primary TMAU, secondary (high-dose) TMAU | Reduce dose, consider alternative energy support |
| Fish Oil (Lecithin) | Contains TMAO or lecithin (choline source) that is converted to TMA. | Depends on lecithin content and individual sensitivity | Primary TMAU, mild enzyme deficiency | Choose high-quality, enteric-coated products; check labels for lecithin |
| Betaine | Gut flora may convert betaine to TMA at very high intake levels. | >12 grams/day (high doses) | Primary TMAU, secondary (high-dose) TMAU | Reduce dose or avoid if odor is an issue |
Managing Supplement-Related Fishy Odor
If you notice a fishy smell after starting a new supplement, the first step is to consult a healthcare provider. They can help determine if the supplement is the cause or if there is an underlying issue like TMAU.
- Reduce or discontinue the supplement: For most people experiencing secondary TMAU due to high supplement intake, lowering the dose or stopping the supplement altogether will resolve the odor.
- Modify your diet: Limit foods that are also rich in TMA precursors. These include eggs, legumes, liver, red meat, and saltwater fish.
- Support FMO3 function: For individuals with mild TMAU or enzyme deficiencies, a doctor might recommend supplements like riboflavin (vitamin B2), which can help improve residual FMO3 enzyme activity.
- Improve gut health: Some approaches focus on altering the gut microbiota to reduce TMA production. Short courses of antibiotics may be used in severe cases, but this is not a long-term solution. A dietitian can help tailor a diet to optimize gut flora.
- Enhance personal hygiene: Use slightly acidic soaps or body washes with a pH between 5.5 and 6.5, and wear loose-fitting, breathable fabrics.
- Consider enteric-coated products: For supplements like fish oil, enteric-coated options can help prevent stomach upset and may reduce the chance of fishy-smelling burps.
Conclusion
A fishy body odor can be a distressing side effect of certain dietary supplements, most commonly high-dose choline, carnitine, and fish oil (especially those with lecithin). The issue arises when the body, particularly in individuals with the genetic condition trimethylaminuria (TMAU) or those consuming excessive amounts, fails to properly metabolize the precursor chemical, trimethylamine (TMA). By being aware of the supplements that can cause this problem and understanding the metabolic pathways involved, individuals can work with a healthcare professional to adjust their intake or manage the underlying condition. For those concerned about this side effect, a careful review of supplement labels and a discussion with a doctor can be key to finding a solution.
For more detailed information, consult the National Center for Biotechnology Information's GeneReviews® on Primary Trimethylaminuria.
