Effect of dietary modifications on lactate threshold and onset of blood lactate accumulation during incremental exercise.

To assess the effect of dietary change on (1) the point at which arterial blood lactate concentration (HLa) increases above the resting value (lactate threshold) and (2) the fixed point corresponding to 4 mM of HLa (onset of blood lactate accumulation; OBLA), five healthy male subjects were put on a mixed diet for 3 days, followed by 4 days of a low carbohydrate diet (a low CHO diet), and then 3 days of a high carbohydrate diet (a high CHO diet). Following each type of diet, the subjects performed a progressive bicycle exercise test, during which concentrations of HLa, pyruvate, FFA, and glucose were analyzed from serial samples of arterial blood, and VO2 was obtained by the Douglas bag method. The results of this study are as follows: FFA was significantly lower, while pyruvate was significantly higher at rest after a high CHO diet than after a low CHO diet (P less than 0.05). These differences continued throughout the incremental exercise, which indicates the incremental contribution of CHO to metabolism after a high CHO diet and vice versa. There was no significant difference in lactate threshold expressed in VO2 among the three conditions. VO2 obtained at OBLA was significantly lower after a high CHO diet than after a low CHO diet (P less than 0.01). It was concluded that the dietary modifications used in this study had no influence on lactate threshold but did affect the point of OBLA. Therefore, dietary conditions should be considered when OBLA is determined using a fixed 4-mM HLa method.