Fish oil and injury: what can it protect?

Most athletes will be injured at some point in their career. Muscle injuries, such as hamstring strains in sprinters, are among the most common, but tendons, ligaments and bones are injured too, and in contact sports concussion is a growing concern. Nutrition cannot prevent most of these injuries. However, what happens after an injury is a different matter. When a limb is immobilised, muscle mass and strength are lost within days, and this is one of the few situations in sports nutrition with a clear and measurable target. Fish oil is often recommended in this context, by supplement companies as well as by practitioners, and it is claimed to reduce muscle loss after injury, to speed up recovery from muscle damage and to protect the brain after a blow to the head. In the first blog of this series we looked at fish oil and muscle in healthy athletes. The evidence from all trials of fish oil in athletes is summarised in do athletes need fish oil supplements?.

In this blog we will explore three different situations: limb immobilisation, exercise-induced muscle damage and concussion. Does fish oil reduce the loss of muscle when a leg is immobilised, and does it slow or speed up recovery afterwards? Does it reduce muscle damage and soreness after hard eccentric exercise? And is there any evidence that it protects the brain?

How much muscle is lost when a limb is immobilised?

Before we can judge a supplement, we need to know the size of the problem. Researchers use different models to study muscle disuse. The most realistic is a real injury or operation, such as an anterior cruciate ligament (ACL) reconstruction or a knee replacement, where the immobilisation is accompanied by inflammation. These studies are difficult to control and to run at any scale. Most studies therefore use uncomplicated disuse in healthy volunteers: bed rest, a leg placed in a cast or brace, or a large reduction in daily step count. The single-leg model is particularly useful because the other leg can serve as a control within the same person.

In one study (1), 24 healthy young men had one leg immobilised in a full leg cast for either 5 or 14 days. Quadriceps cross-sectional area fell by 3.5% after 5 days and by 8.4% after 14 days, and leg lean mass fell by 1.4% and 3.1%. Strength declined much faster than muscle mass: by 9% after 5 days and by 23% after 14 days. Strength depends not only on the amount of muscle but also on how well the nervous system activates it, and this neuromuscular component is lost quickly when a muscle is not used.

Part of the loss of muscle mass is explained by a lower rate of muscle protein synthesis, including a blunted response to protein intake, which is referred to as anabolic resistance. In a previous blog we discussed nutrition for recovery from muscle injury more broadly. It should also be noted that studies in healthy volunteers do not include the inflammation of a real injury or operation, and the losses after a real injury may therefore be larger than these studies suggest.

The link between fish oil, injury and immobilisation

The omega-3 fatty acids EPA and DHA are incorporated into the membranes of muscle cells and into the membranes of the mitochondria inside those cells. Muscle disuse is also thought to impair mitochondrial function. The hypothesis was therefore that fish oil would increase the anabolic response of the muscle and better preserve the mitochondria, and that both would reduce the loss of muscle during disuse.

The key human study was performed in 20 healthy young women with an average age of 22 years (2). They took either 5 g per day of omega-3 fatty acids (about 3 g EPA and 2 g DHA) or the same amount of sunflower oil as a control, starting four weeks before one leg was immobilised for two weeks. The immobilisation was followed by two weeks of return to normal activity. Muscle volume declined by 14% in the control group and by 8% in the omega-3 group. After the two weeks of recovery, muscle volume in the omega-3 group was no longer different from the value before immobilisation, whereas it was still lower in the control group. Muscle mass was reduced in the control group only. Integrated (day-to-day) rates of myofibrillar protein synthesis, the synthesis of the contractile proteins, were higher in the omega-3 group than in the control group at all time points, which may explain the smaller loss of muscle.

"Fish oil reduced the loss of muscle volume during two weeks of leg immobilisation from 14% to 8%, but this is based on a single study in 20 young women."

This is a well-controlled study, but it is only one study, in 20 young women, using an uncomplicated disuse model without the inflammation of a real injury. We do not know whether the results apply to men, to athletes or to an injured and operated knee. However, it must be noted that the dose in the study was very high and this may make it less practical. A typical 1000 mg fish oil capsule contains about 300 mg EPA plus DHA, so 5 g per day would require 16 to 17 capsules a day. Supplementation also started four weeks before the leg was immobilised, because EPA and DHA are incorporated into muscle only gradually. Fish oil can therefore only be considered when a period of immobilisation can be anticipated, for example before scheduled surgery. Starting on the day of an injury is unlikely to have the same effect.

Does fish oil reduce exercise-induced muscle damage?

Exercise-induced muscle damage is a different problem with a different time course. In the first hours after unaccustomed eccentric exercise, the damage is mechanical: myofilaments are overstretched and sarcomeres are disrupted. Over the next one to two days calcium enters the fibre, local inflammation develops and proteolytic systems break down the damaged proteins. Soreness usually peaks after one to three days, and proteins such as creatine kinase (CK) leak from the muscle fibres into the blood. There are two points in this sequence where fish oil could act: the integrity of the cell membrane, and the inflammation. In a previous blog we discussed inflammation in more detail.

The first question is whether fish oil on its own has an effect. In one study (3), 16 moderately trained young men took 5 g per day of fish oil or soybean oil (placebo) for four weeks before and three days after a bout of 12 sets of eccentric knee extension and knee flexion on an isokinetic dynamometer. The exercise reduced peak isometric torque by about 32%. Blood omega-3 concentrations were about 15% higher with fish oil, but there was no effect on CK, inflammation, perceived muscle soreness or muscle function during the three days of recovery.

The next question is whether fish oil works better when it is combined with nutrients that are used for recovery. In a study in competitive football (soccer) players (4), three drinks were compared over six weeks: a drink with fish oil, whey protein (15 g), leucine (1.8 g) and carbohydrate (20 g), the same drink without fish oil, and a carbohydrate drink. After eccentric exercise, perceived muscle soreness over 72 hours was less than half in the fish oil group compared with the protein group, and blood CK was about 60% lower than in the carbohydrate group. The difference in soreness compared with the carbohydrate group, and the difference in CK compared with the protein group, were not statistically significant. There were no differences in muscle function or in football-specific performance tests.

A similar approach was used in 20 professional rugby union players during five weeks of pre-season training (5). The players took a protein-based supplement containing omega-3 fatty acids (551 mg EPA and 551 mg DHA per serving) twice a day, or the same protein-based supplement without omega-3. This is about 2.2 g EPA plus DHA per day, or about 7 capsules of 300 mg. The omega-3 group likely reported less lower-body muscle soreness and, from day 20, less fatigue, and countermovement jump height increased by 4.6% in the omega-3 group while it decreased by 3.4% in the placebo group.

"Fish oil on its own did not reduce muscle damage, but when it was added to a protein supplement, two small studies found less muscle soreness."

So fish oil alone does not appear to affect the markers of muscle damage, whereas adding it to a protein-containing supplement reduced perceived soreness in two applied studies, with some effect on jump performance in one of them and no effect on performance in the other. It is not clear whether the difference is caused by the combination with protein, by the longer supplementation period (five to six weeks rather than four), or by the populations studied. The studies are small and more research is needed to come up with clear recommendations.

Can fish oil protect the brain?

A concussion sets off a sequence of events that includes damage to axons, mitochondrial dysfunction, oxidative stress, inflammation and cell death. Several of these processes are potential targets for omega-3 fatty acids. An important difference from muscle is that DHA, rather than EPA, is the main omega-3 fatty acid in the membranes of the brain. In rodent models of traumatic brain injury, DHA has been reported to reduce the damage to axons (6), which raised the question of whether it could protect athletes who are exposed to repeated head impacts.

In a randomised, double-blind, placebo-controlled study (6), 81 American football players from a National Collegiate Athletic Association (NCAA) Division I team took 2, 4 or 6 g of DHA per day or a placebo over 189 days of a season. A blood marker of damage to axons increased over the season, more in starters than in non-starters, coincident with the periods of more contact and head impacts. DHA supplementation likely attenuated this increase by a small to moderate amount, and this was independent of the dose. Of course, this is just a biomarker, not a concussion. The study did not show that concussions were prevented or that recovery from a concussion was faster. It is also worth noting that even the lowest dose, 2 g DHA per day, is many times more than a standard fish oil capsule provides.

Practical takeaways

• There is only one study that showed that fish oil reduces the loss of muscle volume during two weeks of leg immobilisation and helps restore muscle volume afterwards, and this study was performed in 20 healthy young women.

  
  

• The dose in this study was 5 g of omega-3 fatty acids per day, which is 16 to 17 standard capsules, and supplementation started four weeks before immobilisation, so fish oil can only be considered when a period of immobilisation can be planned, for example before surgery.

  
  

• For exercise-induced muscle damage, fish oil on its own (5 g per day for four weeks) had no effect on CK, soreness or muscle function in one study in moderately trained men.

  
  

• Added to a protein-based supplement for five to six weeks, fish oil reduced perceived muscle soreness in football and rugby players, but the studies are small and the effects on performance were inconsistent.

  
  

• For the brain, DHA rather than EPA is the relevant omega-3 fatty acid, and one randomised study showed a smaller rise in a blood marker of axon damage over a season of American football, which is not the same as protection against concussion.

References

1. Wall BT, Dirks ML, Snijders T, Senden JM, Dolmans J, van Loon LJ. Substantial skeletal muscle loss occurs during only 5 days of disuse. Acta Physiol (Oxf) 210(3) 600-611, 2014.

2. McGlory C, Gorissen SHM, Kamal M, Bahniwal R, Hector AJ, Baker SK, Chabowski A, Phillips SM. Omega-3 fatty acid supplementation attenuates skeletal muscle disuse atrophy during two weeks of unilateral leg immobilization in healthy young women. FASEB J 33(3) 4586-4597, 2019.

3. Mackay J, Bowles E, Macgregor LJ, Prokopidis K, Campbell C, Barber E, Galloway SDR, Witard OC. Fish oil supplementation fails to modulate indices of muscle damage and muscle repair during acute recovery from eccentric exercise in trained young males. Eur J Sport Sci 23(8) 1666-1676, 2023.

4. Philpott JD, Donnelly C, Walshe IH, MacKinley EE, Dick J, Galloway SDR, Tipton KD, Witard OC. Adding fish oil to whey protein, leucine, and carbohydrate over a six-week supplementation period attenuates muscle soreness following eccentric exercise in competitive soccer players. Int J Sport Nutr Exerc Metab 28(1) 26-36, 2018.

5. Black KE, Witard OC, Baker D, Healey P, Lewis V, Tavares F, Christensen S, Pease T, Smith B. Adding omega-3 fatty acids to a protein-based supplement during pre-season training results in reduced muscle soreness and the better maintenance of explosive power in professional Rugby Union players. Eur J Sport Sci 18(10) 1357-1367, 2018.

6. Oliver JM, Jones MT, Kirk KM, Gable DA, Repshas JT, Johnson TA, Andréasson U, Norgren N, Blennow K, Zetterberg H. Effect of docosahexaenoic acid on a biomarker of head trauma in American football. Med Sci Sports Exerc 48(6) 974-982, 2016.