The metabolic root of the odor
The fishy body odor caused by certain supplements is not the supplement itself but a compound produced during its metabolism. The key player is trimethylamine (TMA), an organic compound that has a strong odor often described as fishy or foul.
In a healthy individual, gut bacteria break down certain dietary compounds, such as choline and L-carnitine, into TMA. This TMA is then absorbed and transported to the liver, where an enzyme called flavin-containing monooxygenase 3 (FMO3) converts it into an odorless compound known as trimethylamine N-oxide (TMAO). The TMAO is then excreted harmlessly via urine.
However, a fishy odor can occur when this process is disrupted in one of two ways:
- Genetic predisposition (Trimethylaminuria): Some individuals have a genetic mutation in the FMO3 gene that results in a deficient or non-functional FMO3 enzyme. This means they cannot effectively convert TMA to TMAO, causing TMA to build up and be released through sweat, breath, saliva, and urine, leading to what is known as "fish odor syndrome".
- Overwhelmed enzyme: Even in people with a fully functional FMO3 enzyme, a high intake of supplements can overwhelm the liver's capacity to process all the TMA. This temporary excess of TMA is then excreted through bodily fluids, causing the fishy odor until the supplement load decreases.
Supplements that can cause fishy odor
Choline
Choline is an essential nutrient vital for brain function, nervous system health, and cell membrane formation. However, it is one of the most common supplements to cause a fishy odor, especially with high intake. Some B-vitamin complexes also contain choline and can have a similar effect.
- Mechanism: Gut bacteria readily convert choline into TMA. High choline supplementation or an underlying FMO3 deficiency can lead to an accumulation of TMA.
- Intake: Side effects like fishy body odor are associated with high intakes.
L-Carnitine
L-Carnitine is an amino acid derivative often taken by athletes and bodybuilders to support energy production, fat metabolism, and muscle recovery. It is another well-documented cause of fishy body odor.
- Mechanism: L-Carnitine is converted to TMA by gut bacteria, much like choline. A buildup of TMA due to high intake or impaired FMO3 function causes the odor.
- Intake: Side effects, including a fishy body odor, can occur with high intake. Some brands may recommend lower amounts, but supplement regulations vary, so it's important to consult a healthcare provider.
Betaine
Betaine, also known as trimethylglycine, is a compound found in foods like spinach and beets and is used therapeutically and as a dietary supplement. It is structurally related to choline and can also be converted to TMA by intestinal bacteria.
- Mechanism: High intake of betaine, particularly when used to treat certain medical conditions like homocystinuria, can lead to the production and accumulation of TMA.
- Intake: While generally well-tolerated, high therapeutic intake has been anecdotally associated with a fishy odor.
Comparison of odor-causing supplements
| Feature | Choline Supplements | L-Carnitine Supplements | Betaine Supplements |
|---|---|---|---|
| TMA Precursor | Yes | Yes | Yes |
| Primary Use | Brain function, nerve health, liver support | Fat metabolism, energy, athletic performance | Heart health, amino acid metabolism |
| Mechanism of Odor | Gut bacteria convert choline to TMA | Gut bacteria convert carnitine to TMA | Gut bacteria convert betaine to TMA |
| Common Odor Trigger | High intake, sometimes from B-complex supplements | High intake | High intake, particularly for therapeutic use |
| Associated Condition | Can trigger symptoms in people with TMAU | Can trigger symptoms in people with TMAU | Can trigger symptoms in people with TMAU |
How to manage supplement-induced fishy body odor
If you experience a fishy body odor after starting a supplement, it's best to consult a healthcare professional to rule out any underlying medical conditions. If a supplement is identified as the cause, here are some management strategies:
- Reduce intake: Often, simply lowering the amount of the supplement you take can be enough to allow your body to process TMA more efficiently, eliminating the odor.
- Discontinue use: If reducing intake doesn't help or if the supplement is not essential, stopping it entirely is the most direct way to resolve the odor.
- Dietary changes: Avoid or limit dietary sources of TMA precursors (choline and carnitine), which include red meat, eggs, and certain vegetables, while taking the supplement.
- Activated charcoal: As a supplement, activated charcoal can help absorb excess TMA in the gut, reducing the amount that enters the bloodstream.
- Copper chlorophyllin: Some studies suggest this chlorophyll derivative may also help reduce body odor.
- Probiotics and antibiotics: Some individuals with TMAU may benefit from modifying their gut bacteria with probiotics or, in more severe cases, short-term antibiotics under medical supervision.
- Riboflavin (Vitamin B2): This vitamin can help maximize the activity of the FMO3 enzyme, which is responsible for breaking down TMA.
- Hygiene: Using soaps with a pH close to that of skin (5.5-6.5) can help neutralize the basic TMA on the skin's surface, making it easier to wash away.
Conclusion: Supplement safely
Fishy body odor can be an unwanted and socially distressing side effect of certain dietary supplements, most notably choline, L-carnitine, and betaine. The odor stems from the body's conversion of these compounds into trimethylamine (TMA), which accumulates when the liver's FMO3 enzyme is overwhelmed by high intake or is genetically deficient. By understanding the link between these supplements and TMA, individuals can take proactive steps to manage or eliminate the odor. This includes reducing intake, exploring alternative supplements, making dietary adjustments, and considering supportive supplements like activated charcoal or riboflavin. Consulting a healthcare provider is essential for accurate diagnosis and a personalized management plan. For more general information on dietary supplements, you can consult the NIH Office of Dietary Supplements website.
