Effects of supplemental fish oil on resting metabolic rate, body composition, and salivary cortisol in healthy adults

Background: To determine the effects of supplemental fish oil (FO) on resting metabolic rate (RMR), body composition, and cortisol production in healthy adults. Methods: A total of 44 men and women (34 +/- 13y, mean + SD) participated in the study. All testing was performed first thing in the morning following an overnight fast. Baseline measurements of RMR were measured using indirect calorimetry using a facemask, and body composition was measured using air displacement plethysmography. Saliva was collected via passive drool and analyzed for cortisol concentration using ELISA. Following baseline testing, subjects were randomly assigned in a double blind manner to one of two groups: 4 g/d of Safflower Oil (SO); or 4 g/d of FO supplying 1,600 mg/d eicosapentaenoic acid (EPA) and 800 mg/d docosahexaenoic acid (DHA). All tests were repeated following 6 wk of treatment. Pre to post differences were analyzed using a treatment X time repeated measures ANOVA, and correlations were analyzed using Pearson's r. Results: Compared to the SO group, there was a significant increase in fat free mass following treatment with FO (FO = +0.5 +/- 0.5 kg, SO = -0.1 +/- 1.2 kg, p = 0.03), a significant reduction in fat mass (FO = -0.5 +/- 1.3 kg, SO = +0.2 +/- 1.2 kg, p = 0.04), and a tendency for a decrease in body fat percentage (FO = -0.4 +/- 1.3% body fat, SO = + 0. 3 +/- 1.5% body fat, p = 0.08). No significant differences were observed for body mass (FO = 0.0 +/- 0.9 kg, SO = +0.2 +/- 0.8 kg), RMR (FO = +17 +/- 260 kcal, SO = -62 +/- 184 kcal) or respiratory exchange ratio (FO = -0.02 +/- 0.09, SO = +0.02 +/- 0.05). There was a tendency for salivary cortisol to decrease in the FO group (FO = -0.064 +/- 0.142 mu g/dL, SO = +0.016 +/- 0.272 mu g/dL, p = 0.11). There was a significant correlation in the FO group between change in cortisol and change in fat free mass (r = -0.504, p = 0.02) and fat mass (r = 0.661, p = 0.001). Conclusion: 6 wk of supplementation with FO significantly increased lean mass and decreased fat mass. These changes were significantly correlated with a reduction in salivary cortisol following FO treatment.