Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are the superstars of the essential fatty acid world, and are found primarily in fish and seafood. A tremendous amount of research has investigated the impact of these fatty acids on health and exercise performance. They have been previously discussed in Study Deep Dives #12 for their potential beneficial role in increasing strength and muscle protein synthesis.
Less researched is arachidonic acid (ARA, depicted in Figure 1), the omega-6 cousin to EPA that the body synthesizes from linoleic acid, the plant-based omega-6 found in nuts, seeds, and their oils. It can also be obtained in the diet from meat and eggs, albeit in small amounts.
Reference: Monteiro, J, et al. Food and Function. 2014 Jan.Despite its lesser-known presence in the nutrition world, ARA is an incredibly important and prominent fatty acid in cell membranes. It is found at a level comparable to that of DHA in neural membranes, including in the brain, where it comprises 10-12% of total fatty acids. In skeletal muscle, ARA has been found to make up 15-17% of total fatty acids.
The body relies on ARA for inflammation, a normal and necessary immune response to repair damaged tissue. Specifically, ARA is the precursor to various leukotrienes, prostaglandins, and thromboxanes, collectively known as eicosanoids. While the majority of ARA-derived eicosanoids act to promote inflammation, some also act to resolve it (i.e., are anti-inflammatory). Scientists hypothesize that ARA plays a central role in the adaptive response to strength training. After all, strength training causes an acute inflammatory response that’s necessary to build bigger muscles. For instance, two prostaglandins produced from ARA are PGE2 and PGF2α. Test tube studies performed with skeletal muscle fibers indicate that PGE2 increases protein breakdown while PGF2α stimulates protein synthesis. Other test tube studies have also found PGF2α to increase skeletal muscle fiber growth.
In support of these test tube findings, research in young adults has shown that consuming non-steroidal anti-inflammatory drugs (NSAIDs) after exercise blunts the normal increase in muscle protein synthesis through suppressing the normal increase in PGF2α. In contrast, administration of NSAIDs to older adults has been shown to enhance strength and size gains in response to resistance training by suppressing other forms of inflammation in addition to the beneficial PGF2α. Regardless of outcome, this research does clearly indicate a role of ARA-derived prostaglandins in the adaptive response to exercise.
If blunting ARA-derived prostaglandin formation attenuates adaptations to resistance training in young adults, then perhaps the reverse is also true (as shown in Figure 2)—that increasing prostaglandin formation enhances adaptations to resistance training. Supplementation with ARA increases the ARA content of serum phospholipids. This increased availability is associated with increased prostaglandin formation. Accordingly, the current study was designed to examine whether ARA supplementation affected body composition and muscle function in strength-training individuals. This study also used rats to evaluate the effect of ARA supplementation on anabolic signaling mechanisms.
Arachidonic acid is an omega-6 polyunsaturated fatty acid synthesized in the body from linoleic acid and consumed in the diet from meat and eggs. The body relies on ARA to promote and help resolve inflammation, and some research suggests that blunting ARA-derived inflammation may attenuate skeletal muscle adaptation to resistance training in young adults. This study sought to test the opposite—whether ARA supplementation would enhance adaptations to resistance training.