Consumers are increasingly encouraged to consume more plant-based foods and lower their consumption of foods from animal origin. This shift is driven by environmental and health factors. 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 the age-related reduction in muscle mass and strength is highly prevalent. Adequate dietary intake, specifically protein intake, is a well-known strategy in promoting muscle mass in older adults. Plant-based foods are currently considered to be inferior to animal-based foods in their protein quality, and are therefore considered to be suboptimal for the maintenance of muscle mass at an older age. On the other hand, combining plant-based foods may improve the protein quality and thereby the anabolic properties of a vegan meal. Evidence regarding the anabolic properties of vegan diets in older adults is scarce. As such, the current study aims to assess 1) the effects of a 12-week self-composed vegan diet in comparison to an omnivorous diet on thigh muscle volume (TMV) in community-dwelling older adults and 2) the effect of a 12-week self-composed vegan diet combined with twice-weekly resistance exercise (RE) on TMV in comparison to a self-composed vegan diet without resistance exercise in community-dwelling older adults.

Inclusion Criteria:

• Aged ≥65 years old;
• Community-dwelling;
• BMI 23-32 kg/m2;
• Habitual diet contains animal-based food products (i.e. dairy, meat and/or fish) at least 5 days per week;

Exclusion Criteria:

• Following a self-reported entirely vegetarian or vegan diet during the six months prior to the study;

• Following a prescribed high (≥1.2 g/kg/d) or low protein diet (<0.8 g/kg/d), and/or or taking protein supplements on medical advice, during the month prior to the study;

• Participating in a structured progressive resistance exercise training program the during three months prior to the study;

• ≥4 kg of body weight loss during three months before the start of the study;

• Being diagnosed with one of the following: diabetes mellitus; renal disease; neurological or neuromuscular disorders; serious cardiovascular diseases; cancer (with the exception of the following types of skin cancer: basal cell carcinoma, squamous cell carcinoma); (very) severe chronic obstructive lung disease (COPD; GOLD stage III or IV); bowel disease.

• Chronic use of medication that affects muscle function as assessed by the research physician;

• The use of anticoagulants incompatible for muscle biopsies as assessed by the research physician: acenocoumarol (sintrom); phenprocoumon (marcoumar); dabigatran (pradaxa); apixaban (eliquis); rivaroxaban (xarelto); clopidogrel (plavix); edoxaban (lixiana); combination of acetylsalicylic acid or carbasalate calcium (ascal) with dipyridamole;

• Having a contra-indication to MRI scanning (including, but not limited to):

  • Pacemakers and defibrillators
  • Infraorbital or intraocular metallic fragments
  • Ferromagnetic implants
  • Claustrophobia

• Having a hip prosthesis

• Not willing to stop nutritional supplements, with the exception of supplements on medical advice, and vitamin D;

• Not willing or afraid to give blood, undergo a muscle biopsy or have an MRI scan during the study;

• Unwilling to eat a self-composed vegan diet or an omnivorous diet with daily consumption of animal-based food sources for 3 months;

• Unwilling to participate in RE twice a week for 3 months;

• Currently a research participant in another trial or participated in a clinical trial during one month before the start of the measurement period;

• Not being able to understand Dutch;

• Not having a general physician;

• Working, or having a direct family member that work at the Division of Human Nutrition at Wageningen University during the study.

• Unwilling to be informed about incidental findings of pathology and approving of reporting this to their general physician.