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Effect of fat emulsion infusion and fat feeding on muscle glycogen utilization during cycle exercise

Journal of Applied Physiology 75(4): 1513-1518
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 during exercise. However, on the basis of recent findings, the saturation of fatty acids may influence this response. The purpose of this study was to determine whether saturated or unsaturated fatty acids affected muscle glycogenolysis to varying degrees during cycle exercise. Five healthy men completed three 60-min cycle ergometer trials (EX) at apprx 70% maximal O-2 uptake ( ovrhdot VO-2max). 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; Clintec 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 three-fold increases in free fatty acid (FFA) levels in IL and FF, respectively. Pre-EX muscle glycogen did not differ. The utilization of muscle glycogen during 60 min of EX was less (P lt 0.05) during the FF (60.0 +- 5.2 mmol/kg wet wt) and IL (58.6 +- 6.2 mmol/kg wet wt) compared with CON (81.8 +- 7.5 mmol/kg wet wt). There was no difference between FF and IL in the amount of glycogen utilized. Serum triglyceride levels were greater (P lt 0.05) at preheparin in FF (1.58 +- 0.37 mmol/l) and IL (0.98 +- 0.13 mmol/l) compared with CON (0.47 +- 0.14 mmol/l). Triglyceride levels remained elevated in FF but decreased in IL during EX. FFA increased significantly in FF and IL after heparin and was greater (P lt 0.05) than CON at immediately before EX and at 15, 30, and 45 min of EX. There were no differences in O-2 uptake, heart rate, or kilocalories among the three trials. These results confirm that increasing FFA will spare glycogen during exercise at 70% ovrhdot VO-2max on a cycle ergometer. The magnitude of sparing is not related to the increase in FFA above CON levels, and the sparing appears not to be dependent on the saturation. of FFA.

Accession: 002355603

PMID: 8282597

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