Complementary plant protein pairing does not further increase postexercise myofibrillar protein synthesis after a 20 g protein dose within a high-carbohydrate whole-food matrix in young adults: a randomized controlled trial

Background: Combining plant proteins is a strategy to improve overall amino acid balance; however, the impact of this pairing on postexercise myofibrillar protein synthesis (MPS) remains unclear. Objectives: We compared postexercise MPS after ingestion of beans and rice [complementary pairing of rice and black beans (COMP)] compared with a nutrient-matched mixture of isolated nutrients [isolated mixture of crystallized amino acids, maltodextrin, cellulose, pectin, and soy oil (ISO)]. Methods: In this randomized, crossover trial, 11 physically active adults (24 ± 4 y; 25.0 ± 3 kg/m²; 10 M, 1 F) were randomly assigned (1:1 allocation) to 1 of 2 treatment sequences (COMP-ISO or ISO-COMP). Each trial was separated by ∼1-wk recovery period to allow for muscle biopsy site healing. During primed-constant infusions of L-[ring-¹³C₆]phenylalanine, participants consumed either COMP (548 kcal; 20 g protein, 114 g carbohydrate, 0.8 g fat) or ISO immediately after resistance exercise. Blood and muscle samples were collected at rest and during the 0 to 5 h recovery period to assess outcomes. The primary outcome was MPS. Data were analyzed using linear mixed-effects models. Results: A total of 10 randomly assigned participants completed both arms of the study, whereas 1 participant completed only 1 arm. All participants were included in the final analysis. Postexercise aminoacidemia and net amino acid exposure (incremental AUC) decreased over the 0 to 5 h recovery period regardless of condition (all, P < 0.05). Phosphorylation of AKT^Ser473, 4E-BP1^Thr37/46, rpS6^Ser240/244, and p706k^Thr389 significantly increased at 5 h postexercise in both groups (all P < 0.05). MPS increased from rest but did not differ between COMP (0.057 ± 0.013 %/h) and ISO (0.052 ± 0.013 %/h; P = 0.260; d = 0.4). In an exploratory, cross-trial comparison, MEAT (ground pork) elicited a significantly greater postprandial MPS compared with ISO, COMP, or carbohydrate alone (all, P < 0.05). Conclusions: Post exercise, MPS does not differ after the ingestion of 20 g protein provided as a blend of beans and rice or as a nutrient-matched mix of crystalline amino acids, maltodextrin, soy oil, and fiber in healthy young adults.This study was registered at clinicaltrials.gov as NCT06781723 (https://clinicaltrials.gov/study/NCT06781723).