How is energy expenditure determined?
Energy expenditure is most commonly determined by indirect calorimetry, measuring oxygen consumption and carbon dioxide production, and is expressed as a respiratory quotient (RQ) (ratio of CO2 production to O2 consumption). RQ varies based on the dietary substrate.
RQ for fat is 0.7
RQ for protein is 0.85
RQ for carbohydrates is 1.0
Estimated Energy Requirements Based Upon Age and Weight
The Institute of Medicine has published equations for estimating energy requirements. Such predictions do NOT take in to account energy expenditures in the presence of disease. Fever, malabsorption (e.g. cystic fibrosis) and heart disease, among many other conditions, will all increase energy requirements above these estimates. These calculations are complex and depend upon age, weight, height (over age 3 years) a "physical activity coefficient" assigned to children over age 3 years, based upon their activity. Thus children who "wiggle" even when quiet will have higher energy expenditures than those who sit quietly at a desk.
Estimated Energy Requirements