High-Protein Plant-Based Diet Versus a Protein-Matched Omnivorous Diet to Support Resistance Training Adaptations: A Comparison Between Habitual Vegans and Omnivores.

BACKGROUND Acute protein turnover studies suggest lower anabolic response after ingestion of plant vs. animal proteins. However, the effects of an exclusively plant-based protein diet on resistance training-induced adaptations are under investigation. OBJECTIVE To investigate the effects of dietary protein source [exclusively plant-based vs. mixed diet] on changes in muscle mass and strength in healthy young men undertaking resistance training. METHODS Nineteen young men who were habitual vegans (VEG 26 ± 5 years; 72.7 ± 7.1 kg, 22.9 ± 2.3 kg/m2) and nineteen young men who were omnivores (OMN 26 ± 4 years; 73.3 ± 7.8 kg, 23.6 ± 2.3 kg/m2) undertook a 12-week, twice weekly, supervised resistance training program. Habitual protein intake was assessed at baseline and adjusted to 1.6 g kg-1 day-1 via supplemental protein (soy for VEG or whey for OMN). Dietary intake was monitored every four weeks during the intervention. Leg lean mass, whole muscle, and muscle fiber cross-sectional area (CSA), as well as leg-press 1RM were assessed before (PRE) and after the intervention (POST). RESULTS Both groups showed significant (all p   0.05). CONCLUSION A high-protein (~ 1.6 g kg-1 day-1), exclusively plant-based diet (plant-based whole foods + soy protein isolate supplementation) is not different than a protein-matched mixed diet (mixed whole foods + whey protein supplementation) in supporting muscle strength and mass accrual, suggesting that protein source does not affect resistance training-induced adaptations in untrained young men consuming adequate amounts of protein. CLINICAL TRIAL REGISTRATION NCT03907059. April 8, 2019. Retrospectively registered.