Design and Implementation of the Protein-Distinct Macronutrient-Equivalent Diet (PRODMED) Study: An Eighteen-Week Randomized Crossover Feeding Trial Among Free-Living Rural Older Adults.

Background: Despite growing emphasis on plant-based eating, animal protein consumption remains high among Americans. The biological effects of different dietary protein sources within healthy plant-forward whole-diet patterns are poorly understood, and controlled-feeding methodologies for examining potential impacts are underreported. Objectives: This methods-report describes feasible approaches for menu planning and protein quality assessment within a 2-arm crossover randomized controlled feeding trial over 18 wk among rural Midwestern older adults. The primary trial aims to evaluate the effect of 2 protein-distinct diets on age-related health risk factors. The objectives of this methods-report are to Methods: Participants completed 2 8-wk feeding phases separated by a 2-wk washout; one arm consisting of 162 g/d of lean pork (meat-protein source) and the other an equivalent amount of protein from pulses (plant-protein source). These primary proteins contributed ≥45% of protein intake within a 2000 kcal/d cyclic menu. Data quality, adherence, and participant experience were assessed using descriptive and inferential statistics. Results: Macronutrient distributions of the overall diets were closely matched despite differences in primary protein densities (meat-protein source 261.7 mg/g; plant-protein source 120.6 mg/g). Both diets featured increased fiber but reduced total and saturated fats, sodium, and ultra-processed foods compared to baseline. Consumed energy, though lower than provided, was matched between the intervention arms. Conclusions: Interventions were well-received, reflecting strong participant interest in healthier eating. Results illustrate a practical, scalable method for evaluating specific protein sources within a plant-forward diet, informing future studies and consumer practices.The trials were registered at clinicaltrials.gov as NCT05577858 and NCT05581953.