Vegan and Omnivorous High Protein Diets Support Comparable Daily Myofibrillar Protein Synthesis Rates and Skeletal Muscle Hypertrophy in Young Adults

Abstract

Background: It remains unclear whether non-animal-derived dietary protein sources (and therefore vegan diets) can support resistance training-induced skeletal muscle remodeling to the same extent as animal-derived protein sources.

Methods: In Phase 1, 16 healthy young adults (m = 8, f = 8; age: 23 ± 1 y; BMI: 23 ± 1 kg/m²) completed a 3-d dietary intervention (high protein, 1.8 g·kg bm^-1·d^-1) where protein was derived from omnivorous (OMNI1; n = 8) or exclusively non-animal (VEG1; n = 8) sources, alongside daily unilateral leg resistance exercise. Resting and exercised daily myofibrillar protein synthesis (MyoPS) rates were assessed using deuterium oxide. In Phase 2, 22 healthy young adults (m = 11, f = 11; age: 24 ± 1 y; BMI: 23 ± 0 kg/m²) completed a 10 wk, high-volume (5 d/wk), progressive resistance exercise program while consuming an omnivorous (OMNI2; n = 12) or non-animal-derived (VEG2; n = 10) high-protein diet (∼2 g·kg bm^-1·d^-1). Muscle fiber cross-sectional area (CSA), whole-body lean mass (via DXA), thigh muscle volume (via MRI), muscle strength, and muscle function were determined pre, after 2 and 5 wk, and postintervention.

Objectives: To investigate whether a high-protein, mycoprotein-rich, non-animal-derived diet can support resistance training-induced skeletal muscle remodeling to the same extent as an isonitrogenous omnivorous diet.

Results: Daily MyoPS rates were ∼12% higher in the exercised than in the rested leg (2.46 ± 0.27%·d^-1 compared with 2.20 ± 0.33%·d^-1 and 2.62 ± 0.56%·d^-1 compared with 2.36 ± 0.53%·d^-1 in OMNI1 and VEG1, respectively; P < 0.001) and not different between groups (P > 0.05). Resistance training increased lean mass in both groups by a similar magnitude (OMNI2 2.6 ± 1.1 kg, VEG2 3.1 ± 2.5 kg; P > 0.05). Likewise, training comparably increased thigh muscle volume (OMNI2 8.3 ± 3.6%, VEG2 8.3 ± 4.1%; P > 0.05), and muscle fiber CSA (OMNI2 33 ± 24%, VEG2 32 ± 48%; P > 0.05). Both groups increased strength (1 repetition maximum) of multiple muscle groups, to comparable degrees.

Conclusions: Omnivorous and vegan diets can support comparable rested and exercised daily MyoPS rates in healthy young adults consuming a high-protein diet. This translates to similar skeletal muscle adaptive responses during prolonged high-volume resistance training, irrespective of dietary protein provenance. This trial was registered at clinicaltrials.gov as NCT03572127.

Keywords: hypertrophy; muscle protein synthesis; mycoprotein; resistance exercise; vegan.

FIGURE 1

Flow chart of participant recruitment and allocation within the 2 phases of the experimental protocol. IHC, immunohistochemistry; OMNI, omnivorous; VEG, vegan.

FIGURE 2

Schematic representation of the study protocol. Phase 1, 16 healthy young adults consumed a 3-d fully controlled, eucaloric, and high-protein (1.8 g·kg bm⁻¹·d⁻¹) diet, where the protein was provided predominantly from animal (OMNI1; n = 8) or exclusively non-animal (VEG1; n = 8) sources. During the dietary control period (days: 2–4) participants conducted a single bout of unilateral isokinetic knee extension exercise (5 × 30 contractions) each morning. On day 1, participants consumed 400 mL deuterated water with 50 mL doses consumed daily thereafter. Saliva samples were collected daily, and muscle biopsies were collected from both the rested (straight arrow) and exercised (dashed arrow) legs to determine daily myofibrillar protein synthesis rates. Phase 2, 22 healthy young adults completed a 10-wk high-volume resistance exercise training program, while consuming a high-protein omnivorous diet (OMNI2; n = 12) or a majority non–animal-derived diet (VEG2; n = 10). Participants underwent DXA and MRI scans, muscle biopsies, and strength testing, at regular intervals to characterize resistance exercise-induced muscle adaptations. “D1,” “D2,” etc. refer to day 1, day 2, etc.; “W0,” “W1,” etc. refer to week 0, week 1, etc. OMNI, omnivorous; VEG, vegan.

FIGURE 3

Daily free-living myofibrillar protein synthesis rates (MyoPS) during Phase 1 of the study, calculated from the body water deuterium precursor pool in 16 healthy adults consuming a 3-d fully controlled eucaloric high-protein (1.8 g·kg bm⁻¹·d⁻¹) diet, where the protein was provided predominantly from animal (OMNI1; n = 8) or exclusively non-animal (VEG1; n = 8) sources, in a rested and exercised (single bout of 5 × 30 maximal unilateral isokinetic knee extension contractions on 3 consecutive days) muscle. Values are means, with a standard deviation represented by vertical bars, and individual data points embedded alongside. Data were analyzed with a 2-factor ANOVA, independent samples t-tests, and paired t-tests † indicate the main effect of exercise (P < 0.05). The exercise effect; P < 0.001, treatment effect; P = 0.4647, treatment × exercise interaction effect; P = 0.9621. OMNI, omnivorous; VEG, vegan.

FIGURE 4

Whole-body lean mass and fat mass change (kg) in response to 10 wk of resistance exercise training in healthy young men and women consuming either a high-protein omnivorous diet (OMNI2; n = 12) or a majority non–animal-derived diet (VEG2; n = 10). Values are mean ± SDs, with individual data points embedded alongside. Data were analyzed with 2-factor ANOVAs. ∗Indicates the main effect of time. No differences were observed between the groups. Whole-body lean mass; time effect; P < 0.0001, treatment effect; P = 0.9428, treatment × time interaction effect; P = 0.6124. fat mass; time effect; P = 0.0612, treatment effect; P = 0.3555, treatment × time interaction effect; P = 0.4946. OMNI, omnivorous; VEG, vegan.

FIGURE 5

The whole thigh (A), quadriceps (B), hamstring (C), and adductor (D) muscle volumes at baseline (pre) and following 2, 5, and 10 wk of resistance exercise training (5 times per wk) in healthy young men and women consuming either a high-protein omnivorous diet (OMNI2; n = 12) or a majority non–animal-derived diet (VEG2; n = 9). Values are mean ± SDs, with individual data points embedded alongside. Data were analyzed with 2-factor ANOVAs. ∗ Indicates the main effect of time. No differences were observed between the groups for any of the variables. The time effect; A; P < 0.0001, B; P < 0.0001, C; P < 0.001, D; P < 0.0001. The treatment effect : A; P = 0.9688, B; P = 0.9994, C; P = 0.7671, D; P = 0.9434. Treatment × Time interaction effect; A; P = 0.7099, B; P = 0.7103, C; P = 0.7854, D; P = 0.5752. OMNI, omnivorous; VEG, vegan.

FIGURE 6

Mean muscle fiber cross-sectional area and the change in muscle fiber cross-sectional area in response to 10 wk of resistance exercise training in healthy young men and women consuming either a high-protein omnivorous diet (OMNI2; n = 8) or a majority non–animal-derived diet (VEG2; n = 8). Values are means ± SDs. Data were analyzed with a mixed-effects model ANOVA. ∗ Indicates the main effect of time. No differences were observed between the groups. The time effect; P < 0.05, treatment effect; P = 0.9760, treatment × time interaction effect; P < 0.05. CSA, cross-sectional area; OMNI, omnivorous; VEG, vegan.

FIGURE 7

The percentage change in 1-repetition maximum strength in the deadlift, barbell back squat, incline bench press, and knee extensor peak isometric torque (MVC) after 10 wk of resistance exercise training in healthy young men and women consuming either a high-protein omnivorous diet (OMNI; n = 11) or a majority non–animal-derived diet (VEG; n = 9). Values are mean ± SDs, with individual data points embedded alongside. Data were analyzed with 2-factor ANOVAs. The main effect of training was present for all 3 exercises (P < 0.05). ∗ Indicates the main effect of time. † Indicates a significant difference between groups (P < 0.05). The time effect; deadlift; P < 0.0001, squat; P < 0.0001, incline bench press; P < 0.0001, MVC; P < 0.05. Treatment effect; deadlift; P = 0.7087, squat; P = 0.7271, incline bench press; P = 0.7429, MVC; P = 0.6981. treatment × time; deadlift; P = 0.1396, squat; P = 0.2234, incline bench press; P = 0.1862, MVC; P = 0.9693. MVC, maximal voluntary contraction; OMNI, omnivorous; VEG, vegan.