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

Abstract

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. 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. Nineteen young men who were habitual vegans (VEG 26\u2009±\u20095 years; 72.7\u2009±\u20097.1 kg, 22.9\u2009±\u20092.3 kg/m2) and nineteen young men who were omnivores (OMN 26\u2009±\u20094 years; 73.3\u2009±\u20097.8 kg, 23.6\u2009±\u20092.3 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). Both groups showed significant (all p\u2009<\u20090.05) PRE-to-POST increases in leg lean mass (VEG: 1.2\u2009±\u20091.0 kg; OMN: 1.2\u2009±\u20090.8 kg), rectus femoris CSA (VEG: 1.0\u2009±\u20090.6 cm2; OMN: 0.9\u2009±\u20090.5 cm2), vastus lateralis CSA (VEG: 2.2\u2009±\u20091.1 cm2; OMN: 2.8\u2009±\u20091.0 cm2), vastus lateralis muscle fiber type I (VEG: 741\u2009±\u2009323 µm2; OMN: 677\u2009±\u2009617 µm2) and type II CSA (VEG: 921\u2009±\u2009458 µm2; OMN: 844\u2009±\u2009638 µm2), and leg-press 1RM (VEG: 97\u2009±\u200938 kg; OMN: 117\u2009±\u200935 kg), with no between-group differences for any of the variables (all p\u2009>\u20090.05). A high-protein (~\u20091.6 g kg−1 day−1), exclusively plant-based diet (plant-based whole foods\u2009+\u2009soy protein isolate supplementation) is not different than a protein-matched mixed diet (mixed whole foods\u2009+\u2009whey 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. NCT03907059. April 8, 2019. Retrospectively registered.