Effect of n-3 fatty acids on free tryptophan and exercise fatigue

Free tryptophan (Trp), which is augmented by liberated free fatty acids (FFA) from adipose tissue, can induce mental fatigue via serotonin during exercise. Since an attenuation in FFA has been observed with omega-3 fatty acid (n-3fa) use, our purpose was to examine the effect of n-3fa supplementation on free Trp availability and exercise fatigue. Ten recreationally trained men (n=5) and women (n=5), with maximal oxygen consumption (O_2max)of 51.6 (3.0) and 44.3 (1.4) ml kg^–1 min^–1, respectively, were studied on two occasions following an overnight fast, before and after n-3fa supplementation (4 g day^–1 for 4 weeks). The exercise trials consisted of a 75-min treadmill run at 60% O_2max followed immediately by a high-intensity incremental bout to fatigue. Measurements included exercise monitors, plasma volume (PV), triglycerides (TG), FFA, glycerol, lactate, and glucose. Free Trp and branched-chain amino acids (BCAA) were measured and correlated with time to fatigue; all blood variables were corrected for PV. Free Trp, lactate, glucose, FFA, and glycerol were not significantly different between trials, but TG (P<0.001) and the free Trp/BCAA ratio were significantly lower after n-3fa use 1.76 (0.18)×10^-2 g ml^–1] versus before supplementation 2.17 (0.22), P=0.033]. There was a non-significant increase in time to fatigue after supplementation 10.2 (0.3) min] versus before n-3fa use 9.7 (0.2), P=0.068], and a tendency for higher BCAA levels after supplementation, P=0.068. However, neither free Trp nor the free Trp/BCAA ratio significantly predicted time to fatigue. In conclusion, n-3fa supplementation did not diminish free Trp concentrations or significantly improve endurance performance during a maximal bout of exercise.