EFFECT OF FAT EMULSION INFUSION AND FAT FEEDING ON MUSCLE GLYCOGEN UTILIZATION DURING CYCLE EXERCISE

Elevated plasma fatty acids have been shown to spare muscle glycogen d uring exercise. However, on the basis of recent finding, the saturatio n of fatty acids may influence this response. The purpose of this stud y was to determine whether saturated or unsaturated fatty acids affect ed muscle glycogenolysis to varying degrees during cycle exercise. Fiv e healthy men completed three 60-min cycle ergometer trials (EX) at ap proximately 70% maximal O2 uptake (Vo2 max). Triglyceride levels were elevated by a fat feeding (FF) composed of 90% saturated fatty acids ( heavy whipping cream, 90 g) or by the infusion of Intralipid (IL; Clin tec Nutrition; 45 ml/h of 20% IL, 9.0 g), which was 85% unsaturated. A control trial (CON) consisted of a light breakfast (43 g carbohydrate and 1 g fat). Heparin (2,000 U) was administered 15 min before EX in FF and IL trials, resulting in one- and threefold increases in free fa tty acid (FFA) levels in IL and FF, respectively. Pre-EX muscle glycog en did not differ. The utilization of muscle glycogen during 60 min of EX was less (P < 0.05) during the FF (60.0 +/- 5.2 mmol/kg wet wt) an d IL (58.6 +/- 6.2 mmol/kg wet wt) compared with CON (81.8 +/- 7.5 mmo l/kg wet wt). There was no difference between FF and IL in the amount of glycogen utilized. Serum triglyceride levels were greater (P < 0.05 ) at preheparin in FF (1.58 +/- 0.37 mmol/l) and IL (0.98 +/- 0.13 mmo l/1) compared with CON (0.47 +/- 0.14 mmol/1). Triglyceride levels rem ained elevated in FF but decreased in IL during EX. FFA increased sign ificantly in FF and IL after heparin and was greater (P < 0.05) than C ON at immediately before EX and at 15, 30, and 45 min of EX. There wer e no differences in O2 uptake, heart rate, or kilocalories among the t hree trials. These results confirm that increasing FFA will spare glyc ogen during exercise at 70% Vo2 max on a cycle ergometer. The magnitud e of sparing is not related to the increase in FFA above CON levels, a nd the sparing appears not to be dependent on the saturation of FFA.