Role of Leucine on Muscle Preservation During Weight Loss in Older Men

Participation in this study requires a total of 4 weeks of alternate day fasting (ADF) and 3 laboratory visits (sessions) spread over 5-6 weeks. All sessions are done in a fasted and rested state. Participants will complete 4 weeks of ADF alternating between ad libitum feeding days and fasting days consisting of a small midday meal of up to 600 kcal. Supplements will be provided to participants (3 servings on feeding days and 1 serving on fasting day). Prior to each session, participants are 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. Session 1 * Read and sign consent form * Pre-screening: * Subject screening questionnaire * Global Physical Activity Questionnaire * Body mass * Height * Resting blood pressure and heart rate * Fasting blood glucose (via finger prick) Session 2 The 4-week alternate-day fasting programme will start within 14 days from session 1 * Collection of 4 weeks of supplements * Body mass * Height * Resting blood pressure and heart rate * Fasting blood glucose (via finger prick) * Waist and hip circumference measurements * Body composition using bioelectrical impedance analysis and dual-energy X-ray absorptiometry * Handgrip strength test * Gait speed test * Short physical performance battery * Complete questionnaires on food craving, mood, appetite, hunger, satiety, diet satisfaction, and cognitive function * Blood sample from forearm (35 ml) Session 3 28 days (4 weeks) after the start of alternate-day fasting • Same as session 2 except collection of supplements (not applicable)