Lack of effects of fish oil supplementation for 12 weeks on resting metabolic rate and substrate oxidation in healthy young men: A randomized controlled trial

<div><p>Fish oil (FO) has been shown to have beneficial effects in the body via incorporation into the membranes of many tissues. It has been proposed that omega-3 fatty acids in FO may increase whole body resting metabolic rate (RMR) and fatty acid (FA) oxidation in human subjects, but the results to date are equivocal. The purpose of this study was to investigate the effects of a 12 week FO supplementation period on RMR and substrate oxidation, in comparison to an olive oil (OO) control group, in young healthy males (n = 26; 22.8 ± 2.6 yr). Subjects were matched for age, RMR, physical activity, VO_2max and body mass, and were randomly separated into a group supplemented with either OO (3 g/d) or FO containing 2 g/d eicosapentaenoic acid (EPA) and 1 g/d docosahexaenoic acid (DHA). Participants visited the lab for RMR and substrate oxidation measurements after an overnight fast (10–12 hr) at weeks 0, 6 and 12. Fasted blood samples were taken at baseline and after 12 weeks of supplementation. There were significant increases in the EPA (413%) and DHA (59%) levels in red blood cells after FO supplementation, with no change of these fatty acids in the OO group. RMR and substrate oxidation did not change after supplementation with OO or FO after 6 and 12 weeks. Since there was no effect of supplementation on metabolic measures, we pooled the two treatment groups to determine whether there was a seasonal effect on RMR and substrate oxidation. During the winter season, there was an increase in FA oxidation (36%) with a concomitant decrease (34%) in carbohydrate (CHO) oxidation (p < 0.01), with no change in RMR. These measures were unaffected during the summer season. In conclusion, FO supplementation had no effect on RMR and substrate oxidation in healthy young males. Resting FA oxidation was increased and CHO oxidation reduced over a 12 week period in the winter, with no change in RMR.</p><p><b><i>Trial Registration</i></b>: ClinicalTrials.gov <a href="https://clinicaltrials.gov/ct2/show/NCT02092649" target="_blank">NCT02092649</a></p></div

Resting oxygen consumption (VO₂) (A), resting metabolic rate (RMR) (B), carbohydrate (CHO) oxidation (C), and fatty acid (FA) oxidation (D) normalized to body mass at weeks 0, 6 and 12 of olive oil (OO) and fish oil (FO) supplementation.

<p>Values are reported as means ± SD. There were no differences between the groups.</p

Subject characteristics and blood measurements.

<p>Subject characteristics and blood measurements.</p

Resting metabolic rate, substrate oxidation, and within individual coefficient of variance between consecutive day measurements with fish oil supplementation.

<p>Resting metabolic rate, substrate oxidation, and within individual coefficient of variance between consecutive day measurements with fish oil supplementation.</p

Percent (%) increase in red blood cell (RBC) levels of EPA (A) and DHA (B) in olive oil (OO) and fish oil (FO) groups after 12 weeks of supplementation.

<p>Values are reported as means ± SD.* FO group means were significantly different from the baseline (p < 0.001).</p

Resting oxygen consumption (VO2) (A), resting metabolic rate (RMR) (B), carbohydrate (CHO) oxidation (C), and fatty acid (FA) oxidation (D) normalized to body mass at weeks 0, 6 and 12 in summer and winter groups.

<p>Values are reported as means ± SD. *Significantly different from weeks 0 and 6 (Winter) and weeks 0, 6 and 12 (Summer) (p<0.01).</p

Consort figure illustrating participant flow through the study.

<p>Consort figure illustrating participant flow through the study.</p

Change (%) in resting metabolic rate (RMR) normalized to body mass (BM) after 6 (A) and 12 (B) week supplementation of olive oil (OO) and fish oil (FO).

<p>Values are reported as means ± SD. There were no differences between the groups.</p