The influence of high carbohydrate diets on endurance running performance

Summary

The purpose of the present study was to examine the influence of high carbohydrate (CHO) diets on recovery of endurance capacity following a treadmill run to exhaustion. Two high CHO diets were used, one in which the normal diet was supplemented with complex carbohydrates and the other in which supplementation was achieved with simple carbohydrates. The thirty recreational runners who took part in this study (fifteen men and fifteen women) completed weighed food intake diaries two to three weeks before the start of the study. From an analysis of this information each subject's ‘normal diet’ was prescribed before Trial 1 and then a supplemented diet before Trial 2. The aim was to achieve an increase in carbohydrate content to 70% in the diets of the two high CHO groups and an equivalent increase in energy intake by the Control group. The subjects were required to run to exhaustion on a treadmill at a speed equivalent to 70%$\dot V_{{\text{O}}_{{\text{2max}}} }$ on two occasions separated by 3 days. After Trial 1 the subjects were divided into three equal groups. The Complex CHO group (301±86 mg vs 507±120 mg) and Simple CHO group (265±45 mg vs 462±81 mg) increased their CHO intake by approximately 70% (p<0.05) during the 3 days before Trial 2 whereas the Control group increased their energy intake with additional protein and fat so as to match the energy intakes of the two CHO groups. The Complex CHO group improved their running time to exhaustion during Trial 2 by 26% (105.9±22.4 to 133.3±46.5 min;p<0.01) and the Simple CHO group increased their run time by 23% (114.5±15.6 to 140.6±27.0 min;p<0.01) whereas there was no significant increase in the running time of the Control group (119±19.5 to 122.4±22.4 min). There was no significant difference between the blood lactate and glucose concentrations during the two trials but the plasma FFA concentrations were significantly lower before Trial 2 for the Complex CHO group (0.41±0.15 vs 0.27±0.16 mmol⁻¹;p<0.01) and the Simple CHO group (0.24±0.13 vs 0.19±0.09 mmol⁻¹). The respiratory exchange ratios for the two CHO groups were significantly higher for most of Trial 2 compared with the values obtained during Trial 1. The results of this study have shown that recovery of endurance running capacity is enhanced by an increase in dietary CHO, which can be accomplished by supplementing the normal diet with either simple or complex carbohydrates.