title: On the significance of the respiratory exchange ratio after different diets during exercise in man.
abstract: Total respiratory exchange ratio (R) was compared to the respiratory exchange ratio over the legs (RQL) during exercise after different diets, to evaluate if R (which represents a mean for the whole body) can be used to estimate the relative proportions of fat and carbohydrate oxidation in exercising muscle. One important prerequisite for this is a steady state acid base balance, 7 subjects were studied at rest and during the later part of a 25 min exercise (65% of Vo2 max) on two occasions, the first preceded by a fat rich diet and the second by a carbohydrate rich diet. Oxygen uptake, R and arterial-femoral venous differences for [O2], [CO2], PCO2 and pH and arterial concentrations for lactate and beta-hydroxybutyrate were measured. Respiratory exchange ratio over the exercising legs (RQL) and ventilation/oxygen uptake were calculated. Arterial pH, PCO2, lactate and beta-hydroxybutyrate as well as specific ventilation attained steady levels during the later part of exercise after both diets. Although arterial lactate and beta-hydroxybutyrate differed between the diets, the arterial pH and specific ventilation were the same. Both R and RQL were higher after the carbohydrate than after the fat diet and there was no systematic difference between R and RQL. Therefore, it seems likely that R estimates the proportion of fat and carbohydrate oxidation in skeletal muscle during submaximal exercise after extreme diets.
mesh_terms: D020155:3-Hydroxybutyric Acid; D000328:Adult; D002245:Carbon Dioxide / Q000378:metabolism; D004032:Diet; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D004041:Dietary Fats / Q000008:administration & dosage*; D004734:Energy Metabolism; D005260:Female; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006885:Hydroxybutyrates / Q000378:metabolism; D007773:Lactates / Q000097:blood; D008297:Male; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D010313:Partial Pressure; D005082:Physical Exertion; D012119:Respiration
chemical_list: D004040:Dietary Carbohydrates; D004041:Dietary Fats; D006454:Hemoglobins; D006885:Hydroxybutyrates; D007773:Lactates; D002245:Carbon Dioxide; D010100:Oxygen; D020155:3-Hydroxybutyric Acid