The aim of this study is to assess energy dynamics before and/or after and during Ramadan fasting in non-obese participants. Resting metabolic rate (RMR), thermic effect of food (TEF), active energy expenditure (AEE) and total energy expenditure (TEE) in free-living conditions will be measured . Indirect calorimetry will be used to assess RMR and TEF, doubly labeled water will be used to measure TEE and activity monitors will measure physical activity. In addition, body composition analysis will be performed by bio-electrical impedance. Blood sample will be taken to exclude medical factors affecting energy metabolism.