Benefits
Lean body mass and muscle strength with resistance training
In an 8-week trial, 30 trained men taking arachidonic acid gained more lean body mass, upper-body strength and peak power than a placebo group; part of the funding came from a supplement maker. An earlier 50-day trial in 31 trained men taking 1 gram a day found no significant gain in strength or muscle mass, though anaerobic peak power rose. Results across the two trials are not consistent.
Muscle protein synthesis after a workout
In a 4-week controlled trial, 19 trained men took 1.5 grams a day and then did a resistance-exercise session. Muscle protein synthesis measured over the next 4 hours was no different from placebo, and mTOR signaling was similar in both groups. One marker of ribosome building rose 48 hours later only in the arachidonic acid group.
Muscle fatty acid profile and myogenic gene expression
Over 4 weeks at 1.5 grams a day, blood and skeletal-muscle arachidonic acid levels rose and the mix of membrane fatty acids shifted. Muscle expression of the myogenic genes MyoD and myogenin increased, while markers of basal inflammation in blood and muscle did not rise. This measured tissue and gene changes, not strength or muscle size.
Muscle soreness and recovery after resistance exercise
After 4 weeks at 1.5 grams a day, a hard resistance-exercise session produced a larger short-lived rise in inflammatory markers in blood and muscle than placebo. Despite that, perceived muscle soreness, the drop in muscle force and the time it took to recover were no worse, and recovery was not impaired.
A membrane fatty acid abundant in skeletal muscle
Arachidonic acid is an omega-6 fat built into the membranes of many cells, including skeletal muscle, where it is one of the main fatty acids. From it, cells make eicosanoid signaling molecules, some of which act locally in muscle growth and the exercise response. This membrane and signaling role is the stated rationale behind the muscle trials.
Mechanism of action
Precursor to eicosanoid signaling molecules
Arachidonic acid released from membrane phospholipids is converted by cyclooxygenase and lipoxygenase enzymes into prostaglandins, thromboxanes and leukotrienes. Many of these promote inflammation and platelet aggregation, which is why ARA is described as a pro-inflammatory omega-6, the opposite of the omega-3 fatty acids.
Built into muscle cell membranes
Dietary arachidonic acid is incorporated into the phospholipids of skeletal muscle and blood cells within a few weeks, shifting the membrane fatty acid mix. In muscle, this change has been accompanied by altered expression of genes tied to muscle cell development.
Local signaling in muscle growth and the exercise response
Some prostaglandins made from arachidonic acid act as local signals in skeletal muscle growth and the response to training, which is the proposed reason it was tested for muscle. In a controlled trial, however, it did not raise the acute muscle protein synthesis response to a workout.
Clinical trials
Randomized, double-blind, placebo-controlled trial of 1 g/day arachidonic acid or corn-oil placebo during a 4-day-per-week resistance-training program for 50 days, with muscle biopsies. (Roberts et al. 2007, J Int Soc Sports Nutr)
31 resistance-trained men (16 placebo, 15 arachidonic acid), mean age about 22 years.
Relative anaerobic peak power was greater after 50 days and the inflammatory marker IL-6 was lower after 25 days in the arachidonic acid group, with PGE2 tending to be higher. There were no significant differences between groups in body composition, strength, hormones or markers of muscle hypertrophy. A mixed result overall, with no gain in strength or muscle mass.
Randomized, placebo-controlled trial of arachidonic acid during an 8-week, 3-day-per-week resistance-training program, with a separate acute-signaling study in rats; partially funded by a supplement maker. (De Souza et al. 2016, PLoS One)
30 strength-trained men (arachidonic acid or placebo), mean age about 20 years.
Lean body mass (up 2.9%), upper-body strength (up 8.7%) and peak power (up 12.7%) increased only in the arachidonic acid group versus placebo. The authors noted longer molecular studies are still needed. Part of the funding came from a maker of an arachidonic acid product, and the trial was small and short.
Randomized, double-blind, placebo-controlled trial of 1.5 g/day arachidonic acid or corn-soy-oil placebo for 4 weeks, then a single resistance-exercise bout with muscle protein synthesis measured by stable isotope infusion. (Mitchell et al. 2018, J Appl Physiol)
19 men with at least one year of resistance training.
Muscle protein synthesis over the 4-hour recovery window did not differ between groups, and mTOR pathway signaling was similar. Ribosome biogenesis (45S pre-ribosomal RNA) rose 48 hours after exercise only in the arachidonic acid group. The acute anabolic response to the workout was not increased.
Randomized, double-blind, placebo-controlled trial of 1.5 g/day arachidonic acid or corn-soy-oil placebo for 4 weeks, then systemic and intramuscular inflammatory responses to a resistance-exercise bout. (Markworth et al. 2018, J Appl Physiol)
19 previously resistance-trained men (9 arachidonic acid, 10 placebo).
After supplementation, the exercise bout produced higher creatine kinase, higher blood leukocyte counts and greater inflammatory gene expression in the arachidonic acid group. Despite the larger short-lived inflammatory response, perceived muscle soreness, muscle force loss and recovery time were not worse, and recovery was not impaired.
Randomized, double-blind, placebo-controlled trial of 1.5 g/day arachidonic acid or placebo for 4 weeks in resistance-trained men, with plasma and vastus lateralis biopsies. (Markworth et al. 2018, Prostaglandins Leukot Essent Fatty Acids)
19 resistance-trained men (9 arachidonic acid, 10 placebo).
Supplementation raised arachidonic acid in plasma and skeletal muscle and shifted the membrane fatty acid profile. Muscle expression of the myogenic genes MyoD and myogenin increased, circulating platelet and monocyte counts fell, and markers of basal systemic and intramuscular inflammation did not rise. This tracked tissue and gene changes, not strength or size.