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 O 2 output 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-[ 2 H 2 ]glucose and 1,1,2,3,3-[ 2 H 5 ]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 ( se 0·05) v. 1·67 ( se 0·11) mg/kg per min). During exercise, fish oil reduced the stimulation of both the Rd glucose (5·06 ( se 0·23) v. 6·37 ( se 0·12) mg/kg per min; P <0·05) and HGP (4·88 ( se 0·24) v. 5·91 ( se 0·21) mg/kg per min; P <0·05). Fish oil also reduced glucose metabolic clearance rate (6·93 ( se 0·29) v. 8·30 ( se 0·57) ml/min). Carbohydrate oxidation tended to be less stimulated by exercise after fish oil than after olive oil (12·09 ( se 0·60) v. 13·86 ( se 1·11) mg/kg per min; NS). Lipid oxidation tended to be more stimulated by exercise after fish oil (7·34 ( se 0·45) v. 6·85 ( se 0·17) 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 ( se 0·42) v. 2·94 ( se 0·28) μmol/kg per min) and similarly stimulated by exercise (6·42 ( se 0·75) v. 6·77 ( se 0·72) 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.