Fish Oil & Performance
The first thoughts of most people when it comes to fish oil is regard to inflammation and heart disease, despite the evidence suggesting fish oil does not actually decrease rates of adverse cardiac events. [1]
However, cardiovascular health is not the only area of study that fish oil has fallen under.
More recently, research has investigated the potential role that fish oil may have on your physical performance.
Specifically, this article will cover the effect of fish oil on:
Aerobic fitness
Muscular hypertrophy (muscle growth)
Muscular strength
Finally, this article will cover what dose of fish oil may be required to attain any of these potential benefits.
What is fish oil?
Fish oil is a supplemental form of two specific omega-3 fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
Other means of obtaining these fats through supplements include krill oil and marine-algae oil.
Food sources of omega-3 fatty acids is limited to marine sources, such as fatty fish. Most people do not eat fish regularly enough to get any significant amount of omega-3 fats from their regular diet, which is the rationale for supplementation.
There is another omega-3 fatty acid found in plants, alpha-linolenic acid, but its main purpose is to be converted into EPA and DHA. In that regard, its conversion is quite inefficient.
So, when people discuss omega-3 fats, they are typically referring to EPA and DHA. At least, they should be.
The overarching goal of omega-3 supplementation is to increase your omega-3 index.
This is the percent of your red blood cell membranes that is made up of omega-3 fatty acids. Most sources state that somewhere between 8-12% is a good target.
We’ll discuss this more later in this article in the ‘dosing’ section.
Fish oil’s effect on aerobic fitness
When it comes to performance in aerobic exercise, there are three variables that are most important:
VO2max
Lactate threshold
Movement economy
VO2max is the maximal volume of oxygen you can get out of the air, into your working muscles, and put to use.
One of the specific energy systems used in endurance training relies on oxygen to fuel its energy production. In other words, oxygen is its limiting factor.
The more oxygen you can get into and use through this system, the higher your endurance performance.
Lactate and acid are products of another energy system used in training.
This acid build up can limit further energy production and further muscle contraction. In other words, the higher the use of this energy system, the greater the acid build up, the greater the limitation to further work.
The ability of your body to deal with this lactate and acid build up is known as your lactate threshold.
Movement economy refers to the energy cost to produce a given amount of movement.
For instance, say two people are going for a run that will expend 500 calories worth of energy. The person with higher running economy will go farther than the person with less running economy.
So, where might fish oil have a role here?
At higher doses, fish oil has been shown to improve running economy as measured by a decreased consumption of oxygen and a decreased heart rate for the same workload.
Fish oil also seems to improve blood vessel function and your ability to uptake oxygen by increasing release of nitric oxide. [1]
With that said, evidence on actual endurance performance is inconclusive.
It does seem to be the case that lower doses do not improve running or cycling performance.
There may be a benefit to endurance performance at higher doses, but the evidence here is mixed. This is true whether you look at EPA dominant formulas, DHA dominant formulas, or an even split between the two.
It may be true that this is an instance that is similar to fish oil’s effect on cardiovascular health; in the sense that it improves the marker for the effect rather than the effect itself.
In other words, it could be the classic case of “when the measurement becomes the goal it ceases to be a good measurement.”
Bottom line:
Fish oil seems to improve cardiovascular function during aerobic exercise but may or may not influence performance.
There is probably more benefit than not to supplementing with fish oil for the purpose of aerobic exercise improvements, but the magnitude of benefit is hard to nail down.
Fish oil’s effect on strength & muscle growth
Fish oil supplementation may to be helpful for these goals, but its efficacy seems to depend on the population undergoing the supplementation.
Its effect on strength may also be greater than its effect on muscle growth.
Two randomized control trials looked at fish oil supplementation’s effect on strength & muscle growth in young, trained individuals.
One looked at fish oil’s effect on strength in leg extension while the subjects were undergoing a 40% caloric deficit, meaning they were eating 40% less than their maintenance calories. [2]
The subjects taking placebo saw no changes in strength while the subjects taking fish oil actually saw an increase in strength despite the 40% caloric restriction. There were no changes in muscle mass between the groups
The other paper looked at fish oil’s effect on bench press & squat strength under normal dietary conditions. [3]
The fish oil group saw greater increases in strength on the two lifts compared to the placebo group. There were no differences in muscle growth between the groups.
Similarly, larger reviews of the data on this subject suggest that fish oil may not provide any benefit to muscle growth in young individuals (~<30 years old). [1]
However, in populations more susceptible to poorer muscle health, fish oil may be more beneficial.
For instance, a 2019 study had subjects immobilize one leg for two weeks, a condition known to produce muscle wasting. [4]
There was 14% muscle loss in the placebo group and 8% muscle loss in the fish oil group, on average. This suggests a potentially anti-catabolic (resists breakdown) feature of fish oil.
Another paper looked at strength and muscle growth in sarcopenic women (women who have experienced age-related muscle loss) in response to a resistance training program. [5] Subjects either took fish oil or a placebo.
Those taking fish oil demonstrated noticeably greater muscle growth. However, the gains in strength relative to the placebo group were of an even larger magnitude.
Bottom line:
Fish oil does seem to have some role to play in regard to building muscle and strength.
The effect on strength is likely more pronounced, and the effect both outcomes is greater under conditions that may affect muscle health such as age or immobilization.
Context: where does fish oil rank among other supplements for these goals?
It’s worth noting that fish oil isn’t traditionally considered a performance supplement, and its effect on performance is not going to be as great as the effect you’d get from other choices.
If you are only going to purchase one supplement oriented toward performance, then fish oil may not be the most optimal choice.
That said, there does seem to be real benefit to exercise performance from fish oil and there are other reasons you may choose to use this product.
Ideally, the choice to supplement with fish oil should be made based off the entirety of its effects and how they fit into the puzzle of your life.
Dosing: how much fish oil should you take?
Typically, the goal of supplementing with fish oil is to increase your omega-3 index. [6]
This is the amount of omega-3 fats that are integrated into the cell membrane of your red blood cells, with the ideal range being ~8-12%.
Seemingly, this can be achieved with high doses for a short period of time or low dose for a long period of time.
Most of the research showing benefits to aerobic of strength performance from fish oil supplementation has been shown when the total dose of omega-3 fats is greater than ~3 grams per day. Some of the trials here even tested 4-5 grams per day.
By most people’s standards, this would certainly constitute a high dose.
However, it seems unclear to me if it is this specific dose that provides the benefits or if it is the omega-3 index that does. I don’t see it unreasonable to think that if you were to take a lower dose for a longer time and reached the same omega-3 index that you might see the same benefits from a higher dose for a shorter time.
In research, studies can’t last indefinitely; but your life does. For supplements that may need to be incorporated into cells or tissues, this is the reason why high doses are used.
There just isn’t enough evidence on dosing for these goals specifically for me to give you a good answer on this specific topic.
That said, a dose greater than 1 gram per day of total omega-3s over the course of 12 weeks has been shown to get most people into the ideal omega-3 index. [6]
If you are going to supplement with fish oil, this seems a reasonable lower limit with 2-3 grams / day potentially being better.
If the evidence grows on this subject, I will update this article. To get updates, consider joining the newsletter.
Picking a good fish oil product
There are two things worth looking for in any fish oil product.
First: that the product is third-party tested. This ensures that the label is telling the truth.
Second, look at the amount of EPA and DHA on the label; NOT just the total fats.
For instance, the total fats in the product may be 2 grams, but over half of that may be made up of fats other than omega-3s.
What matters from these products is the dose of omega-3 fats specifically, not the fats of any kind.
References
Jäger R, Heileson JL, Abou Sawan S, et al. International Society of Sports Nutrition Position Stand: Long-Chain Omega-3 Polyunsaturated Fatty Acids. J Int Soc Sports Nutr. 2025;22(1):2441775. doi:10.1080/15502783.2024.2441775
Philpott JD, Bootsma NJ, Rodriguez-Sanchez N, et al. Influence of Fish Oil-Derived n-3 Fatty Acid Supplementation on Changes in Body Composition and Muscle Strength During Short-Term Weight Loss in Resistance-Trained Men. Front Nutr. 2019;6:102. Published 2019 Jul 16. doi:10.3389/fnut.2019.00102
Heileson JL, Machek SB, Harris DR, et al. The effect of fish oil supplementation on resistance training-induced adaptations. J Int Soc Sports Nutr. 2023;20(1):2174704. doi:10.1080/15502783.2023.2174704
McGlory C, Gorissen SHM, Kamal M, et al. Omega-3 fatty acid supplementation attenuates skeletal muscle disuse atrophy during two weeks of unilateral leg immobilization in healthy young women. FASEB J. 2019;33(3):4586-4597. doi:10.1096/fj.201801857RRR
da Cruz Alves NM, Pfrimer K, Santos PC, et al. Randomised Controlled Trial of Fish Oil Supplementation on Responsiveness to Resistance Exercise Training in Sarcopenic Older Women. Nutrients. 2022;14(14):2844. Published 2022 Jul 11. doi:10.3390/nu14142844
Dempsey M, Rockwell MS, Wentz LM. The influence of dietary and supplemental omega-3 fatty acids on the omega-3 index: A scoping review. Front Nutr. 2023;10:1072653. Published 2023 Jan 19. doi:10.3389/fnut.2023.1072653
