# Resistance training increases myofibrillar protein synthesis in middle-to-older aged adults consuming a typical diet with no influence of protein source: a randomized controlled trial

## TL;DR

Resistance training boosts muscle protein synthesis in middle-to-older adults, regardless of whether they consume animal or plant-based protein.

## Contribution

This study shows that resistance training increases muscle protein synthesis in older adults, with no difference based on protein source.

## Key findings

- Resistance training significantly increased myofibrillar protein synthesis rates in trained legs.
- Protein source (animal vs. plant) had no effect on muscle protein synthesis rates.
- Plant-based diet lowered non-HDL cholesterol, but had no other significant metabolic effects.

## Abstract

The primary protein source of a diet may impact skeletal muscle maintenance with advancing age. The impact of the animal and plant protein contents of a typical protein-containing diet on muscle anabolism in middle-to-older aged adults is unknown.

To determine muscle adaptive remodeling response to a 10-d dietary intervention containing divergent protein sources, with and without resistance exercise training (RET) in middle-to-older aged adults.

In a single-blind randomized controlled trial, 27 50- to 70-y-old participants consumed 1.0 g·kg BM−1·d−1 of protein from an animal-focused whey protein–supplemented diet (AW-D) or plant-focused pea protein–supplemented diet (PP-D). Throughout the 10-d diet intervention, unilateral knee extensor RET was performed every other day. Deuterated water ingestion and skeletal muscle biopsies enabled measurement of daily integrated myofibrillar protein synthesis (iMyoPS) rates in the trained and untrained legs. Changes in metabolic rate, body composition, lipid profiles, renal function, whole-body nitrogen balance (WBNB), strength, and muscle architecture were also determined.

Daily iMyoPS rates were significantly greater (P < 0.001) in the trained leg compared with the untrained leg for AW-D (1.44 ± 0.26 vs. 1.29 ± 0.27 %⋅d−1) and PP-D (1.50 ± 0.17 vs. 1.34 ± 0.21 %⋅d−1) with no differences between groups, within leg. Training and diet did not affect intracellular anabolic signaling, muscle architecture, strength, metabolic rate, renal function, or WBNB. Serum non–HDL-cholesterol was significantly (P = 0.014) lower following the intervention for PP-D only (pre: 3.89 ± 0.84; post: 3.37 ± 0.78 mmol⋅L) with no other changes in lipid profiles.

The 10-d provision of 1.0g·kg BM−1·d−1 from predominantly plant-derived or animal-derived protein does not influence daily iMyoPS rates in middle-to-older aged adults and has little impact on metabolic and renal health parameters. RET enhances rates of daily iMyoPS in middle-to-older aged adults consuming a typical protein-containing diet, with no influence of protein source.

ClinicalTrials.gov NCT05574205 (https://clinicaltrials.gov/study/NCT05574205).