Influence of the respiratory quotient adjusted by indirect calorimetry and food consumption on the calculation of energy expenditure by doubly labeled water

Abstract

The aging process leads to a reduction in functional capacity promoting care dependency, incresead prevalence of chronic diseases, influencing quality of life, welfare and nutritional status of the aged people. Accurately evaluating energy metabolism ensures a better adequacy of caloric intake and macronutrients, reducing nutritional risk. The doubly labeled water is the gold-standard method for evaluating total energy expenditure because it doesn't interfere with everyday life activities. The subjects drinks isotopic forms of hydrogen and oxygen and the difference between the elimination rates corresponds to carbon dioxide production, which is converted into energy expenditure by indirect calorimetry equations that include respiratory quotient. The respiratory quotient corresponds to the ratio between carbon dioxide production and oxygen consumption during metabolization of energy substrates. Usually the respiratory quotient is adopted as 0.85 and was thought for the Western diet type that is high in fats, being different from underdeveloped countries. The respiratory quotient can be calculated by indirect calorimetry or by the food quotient, obtained through the individual's food intake. The aim of this study is to evaluate the changes in the total energy expenditure of 40 elderly by a new equation and when we adjust the respiratory quotient by indirect calorimetry and food quotient. It is expected with this study to verify a better adjustment of the respiratory quotient in the equation of total energy expenditure.