FOREARM SUBSTRATE UTILIZATION DURING EXERCISE AFTER A MEAL CONTAININGBOTH FAT AND CARBOHYDRATE

1. Whilst the provision of exogenous carbohydrate has been shown to be beneficial to endurance exercise performance, little attention has be en paid to the possibility of dietary manipulation of the availability of fat. 2. Ten normal subjects were studied on two occasions: after a n overnight fast (postabsorptive state) and after a meal containing 80 g of fat and 80 g of carbohydrate (fed state). Forearm substrate exch ange was studied during 60 min of isometric forearm exercise (5 s cont raction, 5 s relaxation). 3. In the fed state concentrations of plasma triacylglycerol (1510 +/- 150 versus 850 +/- 80 mu mol/l, P<0.01), bl ood ketone bodies (151 +/- 21 versus 80 +/- 10 mu mol/l, P<0.01) and p lasma insulin (17 +/- 3 versus 7 +/- 1 m-units/l, P<0.01) were elevate d compared with the postabsorptive state; plasma glucose and non-ester ified fatty acid concentrations were not significantly different. 4. F orearm blood flow and O-2 consumption each increased about 6-fold duri ng exercise, with no differences between the two nutritional states. T he potential contribution of individual substrates to forearm O-2 cons umption (a calculation which is independent of blood now) was assessed : for triacylglycerol it was significantly greater in the fed state (P <0.01). The sum of the potential contributions of triacylglycerol, non -esterified fatty acids, glucose and ketone bodies to forearm O-2 cons umption was significantly greater, both before and during exercise, in the fed than in the postabsorptive state (P<0.05), implying the spari ng of endogenous (forearm) fuels. 5. These studies highlight the poten tial for manipulation of substrate supply during exercise by feeding m eals containing both carbohydrate and fat.