Similar effects between animal-based and plant-based protein blend as complementary dietary protein on muscle adaptations to resistance training: findings from a randomized clinical trial.

Background: Recent evidence suggests that both animal and plant proteins support strength and hypertrophy gains when paired with resistance training and adequate protein intake. The purpose of this study was to investigate the effects of supplementary protein source (blend of plant-based [PLNT] vs. animal based [ANML]) to habitual diet on changes in muscle mass and strength in healthy young men undertaking resistance training.

Methods: Forty-four young untrained males were recruited for this study. Subjects were randomly allocated into two groups, and consumed three 15-g daily doses (45 g. d-¹ total) of either a mixed plant- (i.e.; soy and pea) or animal-based (i.e.; whey) protein in drink form as a supplementary source of protein in their main meals of the day (i.e.; breakfast, lunch, and dinner) for 12 weeks combined with a 3 times/week linear periodized and supervised resistance training program. Prior to the start of the trial, three (2 nonconsecutive weekdays and 1 weekend day) 24-h dietary recalls were collected to determine baseline habitual protein intake and were repeated during the protocol at weeks 4, 8, and 12. Muscle cross-sectional area (CSA, via ultrasonography imaging) determination, body composition (via dual emission x-ray absorptiometry, DXA), and lower-body maximum dynamic strength (1RM, via leg press) were assessed at baseline (PRE) and after 12 weeks of intervention (POST).

Results: Both groups showed significant (all p < 0.0001) PRE-to-POST increases in whole-body lean mass (PLNT: 2.4 kg ±1.6, ANML: 2.5 kg ±3.9), appendicular lean mass (PLNT: 1.2 kg ±0.2; ANML: 1.8 kg ±0.2) and leg lean mass (PLNT: 0.9 kg ±0.2; ANML: 1.3 kg ±0.2), vastus lateralis mCSA (PLNT: 0.9 cm² ±0.2; ANML: 1.3 cm² ±0.2) and leg-press 1RM (PLNT: 64 kg ±7.8; ANML: 63 kg ±7.5), with no between-group differences for any of the variables (all p > 0.05).

Conclusion: Complementing dietary protein intake with either a blend of plant- or an animal-based protein similarly supported resistance training-induced muscle adaptations.

Trial registration: Distinct Sources of Supplementary Protein in the Resistance Exercise Training-induced Adaptations, NCT05710614, 08/01/2023.