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 diet ary fish oil is a well-known effect, the exact mechanism of this effec t has not been previously studied in human subjects. Therefore, the ai m of this study was (i) to examine the effect of short term fish oil s up supplementation on blood concentrations of ketone bodies, free fatt y acids and triacylglycerol in healthy humans and (ii) to verify wheth er the observed relationships between these variables would be consist ent with reduced lipolysis and/or enhanced hepatic fatty acid oxidatio n after fish oil supplementation. Twenty subjects (21-23 years, normal liver function tests) were randomly divided into two groups to supple ment 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 alread y 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 s ignificant changes in glucose, insulin or ketone body levels were obse rved in either group after supplementation. After fish oil, but not af ter olive oil supplementation, the ratio of blood ketone body levels t o free fatty acid levels increased significantly (P < 0.05). Furthermo re, after fish oil supplementation only, free fatty acid levels were s ignificantly correlated with levels of ketone bodies (day 7 of supplem entation: r = 0.90, P < 0.001) and triacylglycerol (maximum value on d ay 3: r = 0.77, P < 0.01). These findings suggest that reduced lipolys is and increased hepatic beta-oxidation/ketogenesis may contribute to reduced triacylglycerol levels after omega 3 fatty acid supplementatio n in humans. Turnover studies are needed in order to further quantitat e these processes.