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

Abstract

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 1) describe the development of preportioned, ready-to-eat, macronutrient-matched, low ultra-processed, plant-forward, protein-distinct menus aligned with the Dietary Guidelines for Americans for home consumption, and 2) present evidence-based strategies addressing the unique challenges posed by an all-food-provided, protein-distinct intervention.

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.