Project Summary: The present investigation aims to assess resting metabolic rate (RMR) among Saudi population, including children, adolescents, and adults of both sexes. In addition, this research aims to validate common predictive equations that estimate RMR in underweight, normal, overweight, and obese participants. This cross-sectional investigation will involve at least 400 participants from the community. Anthropometric data are going to be collected and RMR is going to be measured by indirect calorimetry for 20 minutes following an overnight fast. Measurements will be conducted in the Lifestyle and Health Research Center using Metalyzer stationary gas analyzer system (Cotrex, Germany). Common predictive equations such as Harris-Benedict, Mifflin-St Jeor, Owen,et al, and, WHO equations will be validated. Habitual physical activity, sleep and sedentary behaviours are going to be measured using validated questionnaire. Body composition will be assessed using dual-energy X-ray absorptiometry (DXA) and bioelectric impedance analysis (BIA)