Influence of diet on CO2 production and ventilation in constant-load exercise.

The coupling between ventilation (VE) and oxygen uptake (VO2) or carbon dioxide production (VCO2) was tested during constant-load cycle ergometry in five healthy, young female volunteers. The ratio of VCO2/VO2 (respiratory quotient, RQ) was altered during exercise by prior dietary manipulation involving three diets: (a) low carbohydrate (L), (b) high carbohydrate (H) and (c) normal, mixed (M) diet. The constant power output selected for a 10-min exercise period approximated 80% of the power output at the anaerobic threshold. At rest and during exercise, the RQ and blood lactate concentration were lower following the L diet than either the H or M diets. All measurements for the H and M diets were similar. In exercise, the VO2 was higher in the L diet (1428 ml/min) than the H diet (1293 ml/min) (P less than 0.05). Although the VCO2 tended to be lower and the VE higher during exercise in the L diet, these values were not significantly different from the H dit. The ratio of VE/VO2 was not different fro the two diets. In the L diet, VE/VCO2 was greater than the H diet (P less than 0.05). A kinetic analysis showed no differences as a consequence of the diets in the rate of adaptation of VO2, VCO2 or VE to the plateau levels. This study has demonstrated an uncoupling of the constant relationship between VE and VCO2 by prior dietary manipulation; however, the relationship between VE and VO2 remained constant in spite of a change in the metabolic RQ which altered VO2 and VCO2 at a constant power output.