EFFECT OF DIETARY FISH-OIL ON BLOOD-LEVELS OF FREE FATTY-ACIDS, KETONE-BODIES AND TRIACYLGLYCEROL IN HUMANS

Although the reduction of serum triacylglycerol concentrations by dietary fish oil is a well-known effect, the exact mechanism of this effect has not been previously studied in human subjects. Therefore, the aim of this study was (i) to examine the effect of short term fish oil sup supplementation on blood concentrations of ketone bodies, free fatty acids and triacylglycerol in healthy humans and (ii) to verify whether the observed relationships between these variables would be consistent with reduced lipolysis and/or enhanced hepatic fatty acid oxidation after fish oil supplementation. Twenty subjects (21-23 years, normal liver function tests) were randomly divided into two groups to supplement their usual diet with either 30 gld of fish oil (n = 11) or olive oil (n = 9). Venous blood samples were drawn after an overnight fast, before and after 1, 3 and 7 d of fish oil/olive oil supplementation. Blood concentrations of triacylglycerol and free fatty acids decreased consistently after fish oil supplementation; the reduction was already significant after one day of fish oil (P < 0.001 for triacylglycerol and P = 0.01 for free fatty acids). In con contrast, neither of these blood values changed after olive oil supplementation (P > 0.10). No significant changes in glucose, insulin or ketone body levels were observed in either group after supplementation. After fish oil, but not after olive oil supplementation, the ratio of blood ketone body levels to free fatty acid levels increased significantly (P < 0.05). Furthermore, after fish oil supplementation only, free fatty acid levels were significantly correlated with levels of ketone bodies (day 7 of supplementation: r = 0.90, P < 0.001) and triacylglycerol (maximum value on day 3: r = 0.77, P < 0.01). These findings suggest that reduced lipolysis and increased hepatic beta-oxidation/ketogenesis may contribute to reduced triacylglycerol levels after omega 3 fatty acid supplementation in humans. Turnover studies are needed in order to further quantitate these processes.