Diet-induced metabolic acidosis and the performance of high intensity exercise in man

Summary

The influence of four isolated periods of dietary manipulation upon high intensity exercise capacity was investigated in six healthy male subjects. Subjects consumed their ‘normal’ (N) diet (45±2% carbohydrate (CHO), 41±3% fat, 14±3% protein) for four days after which they exercised to voluntary exhaustion at a workload equivalent to 100% $\dot V_{{\text{O}}_{{\text{2 max}}} }$. Three further four-day periods of dietary manipulation took place; these were assigned in a randomised manner and each was followed by a high intensity exercise test. The dietary treatments were: a low CHO (3±1%), high fat (71±5%), high protein (26±3%) diet (HFHP); a high CHO (73±2%), low fat (12±2%), normal protein (15±1%) diet (HCLF); and a normal CHO (47±3%), low fat (27±2%), high protein (26±2%) diet (LFHP). Acid-base status and blood lactate concentration were measured on arterialised-venous blood at rest prior to dietary manipulation on each day of the different diets, immediately prior to exercise and at 2, 4, 6, 10 and 15 min post-exercise. Other metabolite concentrations were measured in the blood samples obtained prior to dietary manipulation and immediately prior to exercise. Exercise time to exhaustion after the HFHP diet (179±63 s) was shorter when compared with the N (210±65 s; p<0.01) and HCLF (219±69 s; p<0.05) diets. Exercise time after the LFHP diet (188±63 s) was also reduced when compared with the HCLF diet (p<0.05) but not significantly when compared with the N diet. Immediately prior to exercise after the HFHP diet plasma pH, bicarbonate, blood PCO₂ and base excess levels were lower when compared with the N diet (p<0.05, p<0.001, p<0.001, p<0.001 respectively), the HCLF diet (p<0.05, p<0.001, p<0.01, p<0.001 respectively) and the LFHP diet (p<0.05, p<0.01, p<0.05, p<0.001 respectively). Levels of plasma bicarbonate and blood base excess were also lower after the LFHP diet when compared with the N (p<0.05) and HCLF (p<0.01, p<0.001 respectively) diets. Immediately prior to exercise, plasma free fatty acids (FFA; p<0.001, p<0.01, p<0.05), blood 3-hydroxybutyrate (3-OHB; p<0.05, p<0.05, p<0.05) and plasma urea (p<0.001, p<0.001, p<0.05) were all higher after the HFHP diet when compared with the N, the HCLF and the LFHP diets respectively; plasma total protein was higher when compared with the N diet (p<0.05). The results of the present experiment suggest that dietary composition influences acid-base balance by affecting the plasma buffer base and circulating non-volatile weak acids and by doing so may influence the time taken to reach exhaustion during high intensity exercise.