The effect of a vegan diet with or without resistance exercise on thigh muscle volume in older adults. Research protocol of the Vold-study: a 12-week randomized controlled trial

Background Plant-based diets are increasingly adopted. Plant-based foods exhibit a lower protein quantity and quality compared to animal-based foods. As such, a fully plant-based, i.e. vegan, diet may be suboptimal for the maintenance of skeletal muscle mass later in life. The primary objectives of this study protocol are therefore: 1) To assess the effect of a 12-week self-composed vegan diet in comparison to an omnivorous diet on thigh muscle volume in community-dwelling older adults; and 2) To assess the effect of a 12-week vegan diet combined with twice-weekly resistance exercise (RE) on thigh muscle volume in comparison to a vegan diet without RE in community-dwelling older adults. Methods Seventy-two community-dwelling individuals aged ≥ 65 years with a BMI between 23–32 kg/m² will be included in this randomized controlled trial. Eligible participants will be randomly allocated to either follow their habitual omnivorous diet, a self-composed vegan diet, or a self-composed vegan diet combined with two sessions of RE per week for 12 weeks. Participants will be guided through monthly nutrition information meetings. Dietary intake and physical activity levels will be assessed using food records and accelerometery. The primary study outcome will be thigh muscle volume, assessed at baseline and after 12 weeks using magnetic resonance imaging (MRI). Secondary outcomes will be: body composition, muscle fat infiltration, muscle strength, bone mineral density, bone turnover markers, metabolic profile, insulin levels, cobalamin, iron and vitamin D status, hs-CRP, gut metabolomics and metagenomics, gastro-intestinal symptoms and dietary intake. Measurements will take place at baseline, after 6 weeks, and after 12 weeks. Additionally, mixed muscle protein synthesis rates will be assessed during the first ten days of the intervention using a deuterium oxide protocol. Data will be analysed using independent t-tests and linear mixed models. Discussion The results will provide valuable insights regarding the implications of consuming a vegan diet later in life for skeletal muscle and other health outcomes, and may contribute to the substantiation of the envisaged more plant-based dietary guidelines. Trial registration: The trial is registered at clinicaltrials.gov (NCT05809466; registered on 22 February 2023).