The effect of a single high carbohydrate meal (HCM) and high fat meal (HFM) given 4 h before cycling exercises was determined for performance and metabolism. On the morning of the day of the trial, 10 endurance-trained collegiate males consumed either a single HCM (4669 kj; 79% CHO, 10% F and 11% P) or HFM (4711 kj; 30% CHO, 61% F and 9% P) as a 4 h preexercise meal. The intensity of exercise required was 65% of the maximal oxygen consumption (VO2max) for the first 120 min of exercise, followed by an increased dose of 80% VO2max. Endurance capacity did not differ between the HCM (128 +/- 3 min [SEM]) and HFM (122 +/- 3 min) trials. There was no significant difference in blood glucose levels in the HCM and HFM trials. A significantly higher (p < 0.01) serum insulin level in the HCM trials over the HFM trials was only observed at the start of exercise. Blood lactate levels (< 2.6 mM) during cycling remained below the anaerobic threshold. Respiratory exchange ratio in the HCM trials was significantly higher (p < 0.05 or p < 0.01) than that in HFM trials during the first 40 min of exercise. This was accompanied by significantly lower (p < 0.05 or p < 0.01) levels in serum free fatty acid and beta-HOB for the HCM trial. There was no significant difference between both diet regimens as to heart rate, oxygen consumption and perceived exertion during exercise. These results suggest that a single HCM and HFM given 4 h before exercise influences fuel utilization in the initial stages of prolonged cycling, but these meals may have little effect on endurance capacity.

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