Muscle hypertrophy induced by N-3 PUFA supplementation in absence of exercise: a systematic review of randomized controlled trials

The use of omega-3 polyunsaturated fatty acids (n-3 PUFA) has been studied in physically active population, however, there is a lack of information about the effects of n-3 PUFA supplementation on people with a sedentary behavior or who are undergoing a period of limb immobilization. This systematic review aims to examine the effect of n-3 PUFA on lean mass and muscle protein synthesis (MPS) in absence of physical training. The PubMed, Web of Science, MEDLINE, CINAHL and SPORTDiscus databases were searched following the PRISMA guidelines. Only randomized controlled trials, at least single blind, performed with sedentary humans were considered. Seven studies on a total of 192 individuals were included. Five of the six studies which measured changes in skeletal muscle volume and mass showed higher values with n-3 PUFA. Only two studies measured skeletal muscle protein expression. Both showed beneficial effects of supplementation in muscle protein fractional synthesis rate (FSR), while no effect of n-3 PUFA was observed for mechanistic target of rapamycin (mTOR) and kinase protein (Akt). In addition, ribosomal protein S6 kinase 1 (p70s6k) improved with n-3 PUFA only in one study. Finally, the two studies which measured the skeletal muscle gene expression observed no effect of supplementation.