Glycogen repletion and exercise endurance in rats adapted to a high fat diet

Mar 1, 1990Metabolism: clinical and experimental

How restoring stored energy relates to exercise endurance in rats on a high-fat diet

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Abstract

Fat-adapted rats ran for 115 minutes despite having lower pre-exercise glycogen levels compared to carbohydrate-fed rats.

Adaptation to a high fat diet (78% fat, 1% carbohydrates) did not hinder endurance in rats.
Fat-adapted rats showed similar run times to carbohydrate-fed rats (115 vs. 109 minutes) despite having lower glycogen stores.
After 72 hours of recovery on a high fat diet, muscle glycogen in fat-adapted rats replenished to 42 mumols/g, compared to 52 mumols/g in carbohydrate-fed rats.
Following a diet switch, fat-adapted rats that consumed carbohydrates for 72 hours restored glycogen levels and ran longer (144 minutes) than carbohydrate-adapted rats on a fat diet (104 minutes).
Increased storage and use of intramuscular triglycerides may play a role in endurance adaptation in fat-adapted rats.

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It is well accepted that exercise endurance is directly related to the amount of carbohydrate stored in muscle and that a low carbohydrate diet reduces glycogen storage and exercise performance. However, more recent evidence has shown that when the organism adapts to a high fat diet endurance is not hindered. The present study was designed to test that claim and to further determine if animals adapted to a high fat diet could recover from exhausting exercise and exercise again in spite of carbohydrate deprivation. Fat-adapted (3 to 4 weeks, 78% fat, 1% carbohydrates) rats (FAT) ran (28 m/min, 10% grade) as long as carbohydrate-fed (69% carbohydrates) animals (CHO) (115 v 109 minutes, respectively) in spite of lower pre-exercise glycogen levels in red vastus muscle (36 v 54 mumols/g) and liver (164 v 313 mumols/g) in the FAT group. Following 72 hours of recovery on the FAT diet, glycogen in muscle had replenished to 42 mumols/g (v 52 for CHO) and liver glycogen to 238 mumols/g (v 335 for CHO). The animals were run to exhaustion a second time and run times were again similar (122 v 132 minutes FAT v CHO). When diets were switched after run 1, FAT-adapted animals, which received carbohydrates for 72 hours, restored muscle and liver glycogen (48 and 343 mumols/g, respectively) and then ran longer (144 minutes) than CHO-adapted animals (104 minutes) that ate fat for 72 hours and that had reduced glycogen repletion. We conclude that, in contrast to the classic CHO loading studies in humans that involved acute (72 hours) fat feedings and subsequently reduced endurance, rats adapted to a high fat diet do not have a decrease in endurance capacity even after recovery from previous exhausting work bouts. Part of this adaptation may involve the increased storage and utilization of intramuscular triglycerides (TG) as observed in the present experiment.

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Glycogen repletion and exercise endurance in rats adapted to a high fat diet

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