Chronic supplementation with fish oil increases fat oxidation during exercise in young men

Recent evidence suggests that omega-3 fatty acids from fish oil (FO) stimulate fat oxidation in liver and perhaps skeletal muscle. Our purpose was to examine the effect of an acute high-dose and a chronic low-dose of FO on fat oxidation during exercise. Seven recreationally active males (age 21-27 yr) jogged for 60 min at 60 % VO ₂max in three trials administered in random order: 1) no meal (NM), 2) 4 h following a high-fat meal (HFM), and 3) 4 h following an isocaloric HFM partly substituted with FO (HFM+FO). The FO supplement contained 60 % eicosapentaenoic acid, and 40 % docosahexaenoic acid. Subjects then supplemented 4 g/day of FO for 3 wk and while remaining on the supplementation regimen, repeated the same three trials in random order. Indirect calorimetry was used for the determination of oxygen consumption, respiratory exchange ratio, and energy expenditure from fat and carbohydrate. Heart rate, and rating of perceived exertion were also monitored for each test. The acute high-dose FO had no significant affect on fat use during exercise. In contrast, chronic supplementation significantly augmented total fat energy expenditure as compared to trials before supplementation in each of the three treatments versus trials prior to chronic supplementation (NM, 269.1 ± 49.8 v. 245.7 ± 36.2 Kcal, P = 0.009; HFM, 295.2 ± 40.2 v. 260.8 ± 36.4, P = 0.001; HFM+FO, 299.0 ± 38.7 v. 280.4 ± 35.9 Kcal, P = 0.002). These data suggest that chronic, but not acute FO supplementation enhanced the contribution of lipid during exercise in young active males.