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/m 2 ) and nineteen young men who were omnivores (OMN 26 ± 4 years; 73.3 ± 7.8 kg, 23.6 ± 2.3 kg/m 2 ) 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) PRE-to-POST increases in leg lean mass (VEG: 1.2 ± 1.0 kg; OMN: 1.2 ± 0.8 kg), rectus femoris CSA (VEG: 1.0 ± 0.6 cm 2 ; OMN: 0.9 ± 0.5 cm 2 ), vastus lateralis CSA (VEG: 2.2 ± 1.1 cm 2 ; OMN: 2.8 ± 1.0 cm 2 ), vastus lateralis muscle fiber type I (VEG: 741 ± 323 µm 2 ; OMN: 677 ± 617 µm 2 ) and type II CSA (VEG: 921 ± 458 µm 2 ; OMN: 844 ± 638 µm 2 ), and leg-press 1RM (VEG: 97 ± 38 kg; OMN: 117 ± 35 kg), with no between-group differences for any of the variables (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.