If you're noticing the smell of fish when you open your vegan Omega-3, there's no need to panic. Mighty Kids Supplements uses omega-3 oil derived from algae, and a fishy smell is normal even from plant-based sources. This does not mean that the supplement has gone off or been contaminated; it is just a harmless part of the oxidation process.
The science behind the smell
The molecular structure of omega-3s makes them prone to oxidation into volatile, odorous compounds, which can smell fishy even from entirely vegan sources, like ours at Mighty Kids.
Regardless of the source (fish or algae), the high number of double bonds in omega-3 fatty acids means that they are more likely to oxidise, which is the process of reacting with the air, causing small changes over time. When this happens, secondary oxidation products are formed, and it is these natural, breakdown compounds that can cause a noticeable smell, with notes often likened to seaweed or fish.¹
What breakdown products are responsible?
Experiments have confirmed that the by-products responsible for the fishy odour are a combination of:
- Heptanal
- (E,Z)-3,5-octadien-2-one²
These are volatile compounds, evaporating easily, which is why they can be smelled so strongly even in tiny amounts. They are:
- Harmless at the levels found in oxidised oils
- Naturally occurring in many everyday foods, like oranges and corn
- Regularly used in food flavour and aroma research
Is my omega-3 still safe to consume?
If these oxidation by-products are consumed, they will simply be excreted via one of:
- Sebum (the natural oils produced by your skin)
- Sweat
- Pulmonary excretion (getting rid of the smell-causing compounds by breathing them out; similar in mechanism to onion breath but typically fading much quicker!)
This explains why some individuals might notice a temporary odour (even when the oil itself does not taste or smell fishy) from their scalp, skin or breath.
Odours are not due to:
Fish contamination
- Algae oils contain no fish proteins
Microplastics, or heavy metals
- Neither of these are capable of producing volatile, fishy smells
I'm not noticing a smell, is something wrong with my omega-3?
Whilst experiencing an odour is nothing to worry about, the absence of one is equally harmless; it is something a small subset of individuals experience.
Why do only some people notice a fishy odour?
Individual oxidative stress levels³
People with higher antioxidant capacity experience less lipid oxidation, reducing the formation of volatile, odorous compounds. This can be due to a diet rich in antioxidants or naturally stronger endogenous defences (antioxidants and protective enzymes that the body produces)
Sebum production and skin microbiomes⁴
Individuals who produce fewer natural oils, or with different skin microbial compositions, may excrete fewer volatile compounds via their skin.
Genetic variability⁵
Different people have variations in certain lipid metabolism enzymes which alter both the rate and type of oxidative metabolites produced. Stronger compounds, or faster production could have an influence on noticeable odours.
In summary
For most people, the Mighty Kids Vegan Omega-3 supplement has a mild, lemony flavour, with an inoffensive, "marine-like" smell. A combination of individual differences, such as dietary antioxidants, skin microbiome, absorption, enzymatic metabolism, and dose taken can all explain why some individuals notice a fishy odour with omega-3 supplementation while others do not. Importantly, any such odours noticed are harmless. Omega-3s are such crucial, beneficial nutrients, supporting growth, development and cognitive function, providing healthy fats that the brain and body needs but can't make on its own.
For the sciencey people
More on the molecular structure
Omega-3 fatty acids include EPA and DHA.
EPA: eicosapentaenoic acid
DHA: docosahexaenoic acid
These have a long-chain polyunsaturated molecular structure that is prone to oxidation.
Trimethylaminuria
Trimethylaminuria (TMAU) is a metabolic disorder, known for causing the body to produce a strong, fishy odour. It is genetic, and cannot be caused by taking supplements.
- TMAU is very rare, involving nitrogen metabolism; the DHA/EPA oxidation produces aldehydes and ketones instead of amines.
Evidence limitations
It is extremely unlikely that supplements could play a role in producing odours in people. Currently, however, there are no PubMed systematic reviews or RCTs which directly and exclusively study omega-3 supplementation causing fishy body odour or smell as a primary outcome (especially for algae vs fish sources).
Most of our current evidence on smell comes from mechanistic lab chemistry studies on oxidation of EPA/DHA and odour compound formation.
References
- Hammer, M., & Schieberle, P. (2013). Model studies on the key aroma compounds formed by an oxidative degradation of ω-3 fatty acids initiated by either copper(II) ions or lipoxygenase. Journal of agricultural and food chemistry, 61(46), 10891–10900. https://doi.org/10.1021/jf403827p
- Marsili, R. T., & Laskonis, C. R. (2014). Odorant synergy effects as the cause of fishy malodors in algal marine oils. Journal of agricultural and food chemistry, 62(40), 9676–9682. https://doi.org/10.1021/jf502252q
- Pizzino, G., Irrera, N., Cucinotta, M., Pallio, G., Mannino, F., Arcoraci, V., Squadrito, F., Altavilla, D., & Bitto, A. (2017). Oxidative Stress: Harms and Benefits for Human Health. Oxidative medicine and cellular longevity, 2017, 8416763. https://doi.org/10.1155/2017/8416763
- Grice, E. A., & Segre, J. A. (2011). The skin microbiome. Nature reviews. Microbiology, 9(4), 244–253. https://doi.org/10.1038/nrmicro2537
- Roussel, C., Lessard-Lord, J., Nallabelli, N., Muller, C., Flamand, N., Silvestri, C., & Di Marzo, V. (2025). Human Gut Microbes Produce EPA- and DHA-Derived Oxylipins, but not N-Acyl-Ethanolamines, From Fish Oil. FASEB journal : official publication of the Federation of American Societies for Experimental Biology, 39(12), e70713. https://doi.org/10.1096/fj.202500752RR
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