Fish Oil Supplements and Muscle Growth: Findings Contradict

Fish Oil Supplements and Muscle Growth

Fish oil supplements are believed to help promote muscle growth—but new research shows conflicting results.

One of the many purported health effects of fish oil supplements is the belief that fish oil capsules can help promote muscle growth. However, a new study conducted by researchers at the University of Sterling suggests that fish oil doesn’t seem to affect muscle growth. The initial assumption must be that either this study, or the ones that came before, are flawed somehow. However, this may not necessarily be the case.

The Sterling Study: Fish Oil Supplements and Muscle Growth

  • 20 healthy men were randomized to receive a daily dose of either five grams of fish oil supplements or coconut oil (the control). This was carried out for eight weeks.
  • Participants performed resistance exercises followed by eating 30 grams of whey protein.
  • Muscle biopsies were taken at varying points of the procedure (i.e. following protein ingestion, and following protein ingestion as well as resistance exercises) to measure muscular fat composition and relevant protein activity at rest.
  • Although the fish oil group showed signs of certain enhanced activity in kinase enzymes, there was no significant difference in myofibrillar muscle protein synthesis (MPS) rates between the fish oil capsules group and coconut oil group.

The study looked at whether fish oil supplements enhanced myofibrillar (MPS) in response to protein ingestion. MPS refers to how proteins are created to enhance muscle growth and myofibrillar refers to muscle fibers. In other words, the study examined whether fish oil capsules, combined with dietary protein, enhanced muscle fiber growth more than eating protein alone. This is a very specific hypothesis which, as mentioned previously, is a good thing. There do not appear to be any significant critiques to be made of the methodology employed, save that it was a very small sample size at only 20 participants.

One thing to keep in mind whenever you are looking at a scientific study is that very rarely can studies be assessed on their own. They need to be considered alongside the larger body of research. In this case, and as the authors note, the Sterling study has resulted in findings that seemingly contradict past research that suggests the omega-3 in fish oil capsules are capable of promoting muscle growth. Part of the scientific process is explaining why this might be the case. Fortunately, the researchers have done so.

Possible Explanations for Findings

  • The Sterling study looks only at myofibrillar (MPS) while past research examined mixed muscle proteins. This means that although muscle growth was the target in both cases, the manner it was determined in was different.
  • Not all studies administered their fish oil supplements the same way. Some did so orally, while others through an IV. This could affect how well the oil impacted the body.
  • The Sterling researchers note that whey protein has also been known to highly stimulate MPS activity. They offer the possibility that their use of whey protein boosted MPS activity to a point where the fish oil’s contributions were masked or overwritten.
  • Similarly, it’s possible the resistance exercises alone or in combination with the whey protein pushed MPS activity to a point where the fish oil could not contribute.
  • There is also the issue of a sample size of only 20, meaning pure chance has a larger impact on the results.

Bottom Line

Fish oil supplements may not help promote muscle growth from exercise if taken by healthy young men who are already eating a fair amount of protein. Whether the same could be true of other groups or diets is beyond the scope of the Sterling study.

McGlory, C., et. al., Fish oil supplementation suppresses resistance exercise and feeding‐induced increases in anabolic signaling without affecting myofibrillar protein synthesis in young men, Physiological Reports, 2016, 10.14814/phy2.12715.