Dose Response of Leucine on Muscle Maintenance During Weight Loss

Participation in this study requires a total of 4 weeks of ADF and 6 laboratory visits (sessions) spread over 5-6 weeks. To participate in this study, participants will have to: * complete the questionnaires regarding their health and diet and physical activity level (Global Physical Activity Questionnaire) on session 1, * complete 5 weekly measurements of resting blood pressure and heart rate, fasting blood glucose (via finger prick blood sample), body mass, height, waist and hip circumferences, and body composition using bioelectrical impedance analysis (BIA) on sessions 1 and 3-6, * complete the questionnaires regarding their mood \[Brunel Mood Scale (BRUMS)\], stress \[Perceived Stress Scale (PSS)\], food craving for general and specific foods \[Food Craving Questionnaire-Trait Reduced (FCQ-T-r), and Food Craving Inventory (FCI)\], eating behaviour \[Three-Factor Eating Questionnaire-R18 - cognitive restraint component (TFEQ-r18)\], and appetite, hunger, satiety and diet satisfaction (visual analogue scales, questionnaire and computerised test) twice on sessions 1 and 6, * provide blood samples twice on sessions 1 and 6 for various biomarkers, * complete 2 occasions of body composition measurement using dual-energy X-ray absorptiometry (DXA) on sessions 1 and 6, * complete 4 weeks of ADF as instructed (details given below), * consume only the food provided (high protein diet with leucine supplement) except for ad libitum intake of plain water and zero caloric beverages during the 4 weeks of ADF, * complete daily log of food intake (including leftover/unconsumed food), physical activity and sleep during the entire 4 weeks of ADF, * maintain a consistent diet between session 1 and the start of ADF, * maintain a consistent physical activity level throughout the entire study. Do not start a new exercise programme during the entire duration of the study, and * abstain from high level of physical activity throughout the entire study. Prior to each session except session 2, participants are also required to: * Abstain from any physical activity except activities of daily living for at least 48 hours. * Abstain from alcohol and caffeine for at least 24 hours. * Fast (i.e. do not eat or drink except plain water) overnight for 10 hours. In consideration of the fasting, these sessions will take place in the morning. To control for diurnal variation, the sessions will be timed such that the same measurements will be taken at approximately the same time of the day (+/- 1 hour difference). * Obtain a full night of sleep the night before. The above dietary and physical activity restriction is to minimise the confounding effects of diet and physical activities external to those conducted in this study. Participants will also be instructed to: * Inform the investigators immediately if they fall ill during the study or discover a health condition that requires them to consume any medication, steroids or hormones, and * NOT to take calcium supplements or antacids (e.g. TUMS®) at least 24 hours prior to session 1, and NOT to schedule any scan that involves a contrast agent or ingestion of barium at least 14 days prior to sessions 1 and 6 to ensure accuracy of the DXA scans for body composition. All sessions will be done in a fasted and rested state except session 2. Session 1: • Read and sign consent form * Pre-screening: o Complete questionnaire on health and diet * Resting blood pressure and heart rate * Fasting blood glucose (via finger prick) * Body mass * Height * Complete questionnaires on physical activity level, mood, stress, food craving, eating behaviour, appetite, hunger, satiety and diet satisfaction * Antecubital blood sample * Waist and hip circumference measurements * Body composition using dual-energy X-ray absorptiometry and bioelectrical impedance analysis Session 2: collection of 1 week of food. ADF will start within 10 days from session 1. Body mass and height Session 3: 7 days (1 week) after the start of ADF * Health measurements as in session 1: * Resting blood pressure and heart rate * Fasting blood glucose (via finger prick) * Body mass and height * Waist and hip circumferences * Body composition using bioelectrical impedance analysis * Collection of 1 week of food Session 4: 14 days (2 weeks) after start of fasting programme • Same as session 3 Session 5: 21 days (3 weeks) after start of fasting programme • Same as session 3 Session 6: 28 days (4 weeks) after start of fasting programme • Same as session 1 except consent and pre-screening questionnaires on health and diet, and physical activity level are not applicable