A fifth study day was added to measure protein requirements of included individuals to be able to interpret their response to the other interventions on the other study days, and to test the hypothesis that subjects with lower protein requirements respond less to intervention with leucine and/or carbohydrates. For the 5th additional test day we will first approach the 10 COPD and 10 healthy subjects who already completed the first 4 study days (and signed the re-contact form) to come back for this extra test day. We will (pre-)screen these subjects by phone for eligibility and check for changes in their recent medical history (with help of the (pre-)screening questionnaires in CRF). If all inclusion criteria are still met, these subjects will be asked to provide a written re-consent. If necessary, we will recruit new subjects who will complete only one of the four test days (i.e. the test day on which the hydrolyzed casein-based protein meal with carbohydrates is provided) and the additional 5th study day.