Semistarvation and exercise.

Nutritional intake plays an important role in determining metabolic and respiratory demands during both rest and exercise. This study examines the effects in normal subjects of 4 days of semistarvation with 440 kcal/day of intravenously infused dextrose followed by the infusion of 480 kcal/day of amino acids for 48 h on the metabolic and ventilatory response to exercise (1.25, 2.50, and 5.0 kg . m/s.). After 4 days of the dextrose infusion, arterial PCO2 (P less than 0.05), and the ventilatory equivalent for CO2 (VE/VCO2, P less than 0.05) were decreased at rest compared with control measurements made prior to the dextrose infusion. During all three levels of steady-state exercise, arterial PCO2 was significantly lower (P less than 0.05) than observed before the start of the dextrose infusion. The subsequent infusion of amino acids resulted in increases in O2 consumption (V02; P less than 0.05) and minute ventilation (VE; P less than 0.05), a decrease in arterial PCO2 (P less than 0.05), and little change in CO2 production (VCO2) at rest. During low levels of exercise, compared with the values obtained following the 4 days of dextrose infusion, there were larger increases in VE and VO2, whereas VCO2 changed little. Mechanical efficiency (kcal work/kcal energy utilized) during exercise increased after 4 days of dextrose and returned to near control levels with the amino acid infusion. The adaptive response characteristic of semistarvation with dextrose appears to be altered when isocaloric amounts of amino acids are subsequently administered for short periods.