High-protein intake and physical activity are important approaches to preserve muscle mass. Consuming high levels of high-quality proteins to preserve muscle mass is challenging with a plant-based diet. Healthy, older participants will follow a twelve-week high-protein vegetarian diet or high-protein omnivorous diet both in combination with a resistance training program. The change in protein intake and muscle mass will be assessed.

Inclusion Criteria:

• Aged 55 years or older
• BMI 18.5-30 kg/m2
• Living independently
• Ability and willingness to comply with the protocol
• Written an informed consent
• Consent of the study physician

Exclusion Criteria:

• Alcohol abuse (more than 14 glasses per week (women) or more than 21 glasses per week (men)) or drug abuse in the opinion of the study physician (CBS et al., 2017)
• Inability to understand the Dutch language
• Cognitive impairment (MMSE more than 25)
• Diagnosed chronic disease that may interfere with protocol (e.g., cardiovascular, gastrointestinal, neurological, known renal diseases (eGFR more than 60 mL/min), and/or diabetes)
• Underwent bariatric surgery
• Current enrolment in an exercise program or other intervention study
• Planned a holiday during the intervention period and is unable to attend training sessions for more than 1 week