THE ACUTE REVERSAL OF A DIET-INDUCED METABOLIC-ACIDOSIS DOES NOT RESTORE ENDURANCE CAPACITY DURING HIGH-INTENSITY EXERCISE IN MAN

The present experiment was designed to investigate whether a diet-indu ced metabolic acidosis was a major factor in the earlier onset of fati gue during high-intensity exercise. Six healthy males cycled to exhaus tion at a workload equivalent to 95% of maximum oxygen uptake on four separate occasions. Exercise tests were performed after an overnight f ast and each test was preceded by one of four experimental conditions. Two experimental diets were designed, either to replicate each subjec t's own normal diet [TN diet, mean (SD) daily energy intake (E) = 13 ( 0.7) MJ, 14.5 (0.8)% protein (Pro), 37.5 (2.2)% fat (Fat) and 47.5 (2. 1)% carbohydrate (CHO)], or a low-carbohydrate diet [E = 12.6 (0.8) MJ , 33.6 (1.3)% Pro, 64.4 (1.5)% Fat and 2.2 (0.4)% CHO]. These diets we re prepared and consumed within the department over a 3-day period. Ov er a 3-period prior to the exercise trial subjects ingested either NaH CO3 or CaCO3 (3.6 and 3.0 mmol . kg body mass), thus giving four exper imental conditions: N diet and treatment, N diet and placebo low-CHO d iet and treatment and low-CHO diet and placebo. Treatments were assign ed using a randomised protocol. Arterialised venous blood samples were taken for the determination of acid-base status and metabolite concen trations at rest prior to exercise and at intervals for 30 min followi ng exhaustion. Consumption of the low-CHO diet induced a mild metaboli c acidosis which was reversed by the ingestion of NaHCO3. Blood pH, bi carbonate (HCO3-) and base excess (BE) were higher following NaHCO3 in gestion after the normal diet than all of the other experimental condi tions (P < 0.01). Exercise time following the low-CHO diet was less th an on the normal diet conditions (P < 0.05): bicarbonate ingestion had no effect on exercise time on either of the diet conditions. Post-exe rcise blood pH: HCO3- and BE were higher following the ingestion of Na HCO3 irrespective of the pre-exercise diet (P < 0.05). Blood lactate c oncentration was higher 2 min after exercise following the N diet with NaHCO3 when compared to the low-CHO diets with either NaHCO3 or place bo (P < 0.05). Plasma ammonia accumulation was not significantly diffe rent between experimental conditions. These data confirm previous data showing that the ingestion of a low-CHO diet reduces the capacity to perform high-intensity exercise, but it appears that the metabolic aci dosis induced by the low-CHO diet is not the cause of the reduced exer cise capacity observed during high-intensity exercise under these cond itions.