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

Abstract

Background: 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.

Objectives: 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.

Methods: 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.

Results: 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.

Conclusions: 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.

Clinical trial registry number: ClinicalTrials.gov NCT05574205 (https://clinicaltrials.gov/study/NCT05574205).

Keywords: animal protein; human physiology; muscle anabolism; plant protein; resistance exercise; sarcopenia.

FIGURE 1

CONSORT flow diagram. BM, body mass; DXA, dual-energy X-ray absorptiometry; RMR, resting metabolic rate.

FIGURE 2

Schematic overview of the study timeline. Overview of the study design with 5-d habitual measurement phase and 10-d intervention phase of controlled diet and RET. BM, body mass; AW-D, animal-focused whey protein–supplemented diet; D₂O, deuterated water; DXA, dual-energy X-ray absorptiometry; MVC, maximal voluntary contraction; PP-D, plant-focused pea protein–supplemented diet; RET, resistance exercise training; RMR, resting metabolic rate.

FIGURE 3

Deuterium enrichment in myofibrillar alanine and body water pool. Time course of saliva enrichment over the 10-d intervention following D₂O loading in atom percent excess (APE) (A). Two-way analysis of variance showed a significant effect of time (P < 0.001) but no main effect for group (P = 0.910) or interaction (P = 0.214). Mean whole-body water deuterium (²H) enrichment from saliva sampling during the intervention (day −1 to day 10 of intervention) following the loading phase (B). An independent-samples t test unveiled no significant difference in total body water enrichment between animal-focused whey protein–supplemented diet (AW-D) or plant-focused pea protein–supplemented diet (PP-D) groups (P = 0.907). Myofibrillar-bound alanine enrichment in moles percent excess for UT (untrained) and T (trained) leg from days 0 to 10 (C) with no significant interaction (P = 0.964) or group effect (P = 0.733) but a main effect for training (∗∗P < 0.001). Significance was set at P ≤ 0.05. Data are shown with individual data points for n = 13 for AW-D (black circles) and n = 12 for PP-D (white triangles) and plotted as the mean ± SEM.

FIGURE 4

Integrated daily myofibrillar protein synthesis (iMyoPS) rates over 10-d intervention of dietary intervention with divergent protein sources, alone or with combined unilateral resistance exercise training. Daily integrated myofibrillar protein synthesis (iMyoPS) fractional synthesis rate (FSR) over a 10-d period untrained (UT; gray bar and black circles) and trained (T; white bar and white triangles) legs (A) in both animal-focused whey protein–supplemented diet (AW-D) and plant-focused pea protein–supplemented diet (PP-D). Connected black circles and white triangles show individual responses to training, within conditions. Two-way repeated-measures analysis of variance showed no interaction (P = 0.936), or main group effect (P = 0.527) but a significant effect of training (∗∗P < 0.001). Delta change in iMyoPS rates for T relative to UT visualized in (B). An independent-samples t test was used to compare differences in iMyoPS between T and UT where there were no differences between groups (P > 0.05). Significance was set at P ≤ 0.05. Data are shown with individual data points for n = 13 for AW-D (circles) and n = 12 for PP-D (triangles) and plotted as the mean ± SEM for (A) and (B).

FIGURE 5

Immunoblots from trained and untrained leg pre- and postintervention for anabolism-related protein targets. Changes in protein expression for phosphorylated (p)-Akt^Ser473/total (t)-Akt (A), p-mTOR^Ser2448/t-mTOR (B), and p-eEF2^Thr56/t-eEF2 (C) in the postabsorptive state expressed as the post- minus preintervention value for trained (T) and untrained (UT) legs. Data are expressed relative to the respective relative total protein, after accounting for loading control and shown as fold change from own leg at pre-, as an internal control, which was normalized to 1. Two-way analysis of variance was used to compare between groups (animal-focused whey-supplemented; AW-D and plant-focused pea supplemented (PP-D) and legs (T and UT). A significant main training effect (P=0.015) for p-eEF2^Thr56/t-eEF2, which did not remain for the Bonferroni post hoc test (AW-D: P = 0.094, PP-D: P = 0.059). No other significant differences between legs or groups were observed (all P > 0.05). Significance was set at P ≤ 0.05. Data are shown with individual data points and SEM with individual data points for n = 13 for AW-D and n = 12 for PP-D for (A–C). AW-D, animal-focused whey protein–supplemented diet; PP-D, plant-focused pea protein–supplemented diet.

FIGURE 6

Whole-body nitrogen balance (WBNB) determined from urinary nitrogen excretion and ingested nitrogen (from dietary protein) prior to (pre) and following (post) a 10-d animal-focused whey protein–supplemented diet (AW-D) and plant-focused pea protein–supplemented diet (PP-D) (A). A 2-way ANOVA was used to test for significant differences between AW-D and PP-D, pre- and postintervention with no main interaction (P = 0.436), group (P = 0.910) or time effect (P = 0.746). Delta change in WBNB from pre- to postintervention (B). An independent-samples t test was run to test differences between AW-D and PP-D in WBNB change from baseline, with no significant difference between groups (P > 0.05). Significance was set at P ≤ 0.05. Data are shown with individual data points for n = 14 for AW-D (circles) and n = 13 for PP-D (triangles) with bars showing the mean ± SEM for (A) and (B). T, trained; UT, untrained.