Fish-oil supplementation reduces stimulation of plasma glucose fluxes during exercise in untrained males

Abstract

The present study examined the effects of a 3-week fish-oil supplementation (6 g/d) on the rate of plasma glucose disappearance (Rd glucose), hepatic glucose production (HGP), carbohydrate oxidation and lipid oxidation during exercise. Six untrained males (23±1 years; 67·6±2·7kg) performed two 90min cycling exercise sessions at 60% of maximal O2output separated by 20 d. During the 20 d before the first test, they ingested 6g olive oil/d, then 6g fish oil/d during the 20 d before the second test. Plasma glucose fluxes and lipolysis were traced using 6,6-[2H2]glucose and 1,1,2,3,3-[2H5]glycerol respectively. Substrates oxidation was obtained from indirect calorimetry. At rest HGP and the Rd glucose were similar after olive oil and fish oil (1.83 (se0·05)v.1·67 (se0·11) mg/kg per min). During exercise, fish oil reduced the stimulation of both the Rd glucose (5·06 (se0·23)v.6·37 (se0·12) mg/kg per min;P<0·05) and HGP (4·88 (se0·24)v.5·91 (se0·21) mg/kg per min;P<0·05). Fish oil also reduced glucose metabolic clearance rate (6·93 (se0·29)v.8·30 (se0·57) ml/min). Carbohydrate oxidation tended to be less stimulated by exercise after fish oil than after olive oil (12·09 (se0·60)v.13·86 (se1·11) mg/kg per min; NS). Lipid oxidation tended to be more stimulated by exercise after fish oil (7·34 (se0·45)v.6·85 (se0·17) mg/kg per min; NS). Glycaemia, lactataemia, insulinaemia and glucagonaemia were similarly affected by exercise after fish oil and olive oil. Lipolysis at rest was similar after fish oil and olive oil (2·92 (se0·42)v.2·94 (se0·28) μmol/kg per min) and similarly stimulated by exercise (6·42 (se0·75)v.6·77 (se0·72) μmol/kg per min). It is concluded that fish oil reduced the Rd glucose by 26% by reducing glucose metabolic clearance rate, possibly by facilitating fat oxidation, and reduced HGP by 21%, possibly by a feedback mechanism.