Dietary omega-3 fatty acid supplementation increases the rate of muscle protein synthesis in older adults: a randomized controlled trial

Abstract

Background: Loss of muscle mass with aging is a major public health concern. Omega-3 (n-3) fatty acids stimulate protein anabolism in animals and might therefore be useful for the treatment of sarcopenia. However, the effect of omega-3 fatty acids on human protein metabolism is unknown.

Objective: The objective of this study was to evaluate the effect of omega-3 fatty acid supplementation on the rate of muscle protein synthesis in older adults.

Design: Sixteen healthy, older adults were randomly assigned to receive either omega-3 fatty acids or corn oil for 8 wk. The rate of muscle protein synthesis and the phosphorylation of key elements of the anabolic signaling pathway were evaluated before and after supplementation during basal, postabsorptive conditions and during a hyperaminoacidemic-hyperinsulinemic clamp.

Results: Corn oil supplementation had no effect on the muscle protein synthesis rate and the extent of anabolic signaling element phosphorylation in muscle. Omega-3 fatty acid supplementation had no effect on the basal rate of muscle protein synthesis (mean ± SEM: 0.051 ± 0.005%/h compared with 0.053 ± 0.008%/h before and after supplementation, respectively; P = 0.80) but augmented the hyperaminoacidemia-hyperinsulinemia-induced increase in the rate of muscle protein synthesis (from 0.009 ± 0.005%/h above basal values to 0.031 ± 0.003%/h above basal values; P < 0.01), which was accompanied by greater increases in muscle mTOR(Ser2448) (P = 0.08) and p70s6k(Thr389) (P < 0.01) phosphorylation.

Conclusion: Omega-3 fatty acids stimulate muscle protein synthesis in older adults and may be useful for the prevention and treatment of sarcopenia. This trial was registered at clinical trials.gov as NCT00794079.

FIGURE 1.

Mean (±SEM) mixed skeletal muscle protein fractional synthesis rate (FSR), calculated by using the average plasma free phenylalanine enrichment as the precursor pool enrichment, during basal, postabsorptive conditions and during the hyperaminoacidemic-hyperinsulinemic clamp before and after 8 wk of supplementation with either corn oil (n = 7) or omega-3 fatty acids (n = 8). There was no difference in the muscle protein FSR between the omega-3 fatty acid and corn oil groups before the intervention [ANOVA showed a significant effect of clamp (P < 0.001), no significant effect of group (P = 0.47), and no interaction (P = 0.60)]. ^aIn the corn oil group, ANOVA showed a significant main effect of clamp (P < 0.01). In the omega-3 fatty acid group, ANOVA showed a significant effect of clamp (P < 0.01) and an interaction (P < 0.001), which was followed by Tukey's post hoc analysis. ^bSignificantly different from the corresponding basal value, P < 0.01. ^cSignificantly different from the corresponding value before omega-3 fatty acid supplementation, P < 0.01. Furthermore, the before-after intervention change in the anabolic response (increase in the muscle protein FSR from basal values) was significantly greater in the omega-3 fatty acid group than in the corn oil group (P = 0.01, Student's t test for independent samples).

FIGURE 2.

Mean (±SEM) concentrations (arbitrary units) of mTOR^Ser2448 and p70s6k^Thr389 during basal, postabsorptive conditions and during the hyperaminoacidemic-hyperinsulinemic clamp before and after 8 wk of supplementation with either corn oil (n = 7) or omega-3 fatty acids (n = 8). ^aANOVA showed a significant main effect of clamp (P < 0.01). ^bANOVA showed a significant main effect of time (P < 0.05). ^cThere was a trend for a greater clamp-induced increase in mTOR^Ser2448 after omega-3 fatty acid supplementation than before supplementation (interaction: P = 0.08). ^d,eANOVA showed a significant interaction (P < 0.05), which was followed by Tukey's post hoc analysis. ^dSignificantly different from corresponding basal value, P < 0.05. ^eSignificantly different from corresponding value before omega-3 fatty acid supplementation, P < 0.05. Furthermore, the before-after intervention changes in the insulin/amino acid–mediated increase in p70s6k and mTOR phosphorylation above basal values were greater in the omega-3 fatty acid group than in the corn oil group (P < 0.05 and P = 0.07, respectively; Mann-Whitney U test).