Consumers are increasingly encouraged to consume more plant-based foods and lower their consumption of foods from animal origin. However, the consequences of such a transition on muscle mass still remains to be explored. This is of particular importance in the older population, where sarcopenia is highly prevalent. The aim of this randomized controlled cross-over study is to investigate the short-term effect of a 10-day controlled vegan diet on daily muscle fractional synthesis rates in comparison to a 10-day controlled omnivorous diet in 35 community-dwelling older adults.

Participants will follow a fully controlled vegan diet, directly followed by a fully controlled omnivorous diet for 10 days, or vice versa. Researchers will compare the effect of the vegan diet to the effect of the omnivorous diet.

Inclusion Criteria:

• Aged 65-79 years old;
• Community-dwelling;
• BMI 20-35 kg/m^2.

Exclusion Criteria:

• Following a vegetarian or vegan diet during the six months prior to the study;
• Following a diet that affects protein intake during the six months prior to the study;
• Participating in a structured exercise training program in the past three months;
• 5% or more body weight loss during three months before the start of the study;
• Being diagnosed with one of the following: diabetes; renal disease; neurological or neuromuscular disorders; serious cardiovascular diseases; cancer; chronic obstructive lung disease (COPD);
• Chronic use of medication that affects muscle function, e.g. corticosteroids, metformin, insulin;
• The use of the following medicines: acenocoumarol (sintrom); phenprocoumon (marcoumar); dabigatran (pradaxa); apixaban (eliquis); rivaroxaban (xarelto); clopidogrel (plavix); combination of acetylsalicylic acid or carbasalate calcium (ascal) with dipyridamole.
• Allergic or intolerant to any product included in the diets;
• Not willing to stop nutritional supplements, with the exception of supplements on medical advice, and vitamin D;
• Not willing or afraid to give blood or undergo a muscle biopsy during the study;
• Unwilling to eat a vegan and an omnivorous diet for ten days each;
• Currently a research participant in another trial or participated in a clinical trial during three months before the start of the measurement period;
• Not being able to understand Dutch;
• Not having a general physician.