Soy-Dairy Protein Blend or Whey Protein Isolate Ingestion Induces Similar Postexercise Muscle Mechanistic Target of Rapamycin Complex 1 Signaling and Protein Synthesis Responses in Older Men

Abstract

Background: Previous work demonstrated that a soy-dairy protein blend (PB) prolongs hyperaminoacidemia and muscle protein synthesis in young adults after resistance exercise.

Objective: We investigated the effect of PB in older adults. We hypothesized that PB would prolong hyperaminoacidemia, enhancing mechanistic target of rapamycin complex 1 (mTORC1) signaling and muscle protein anabolism compared with a whey protein isolate (WPI).

Methods: This double-blind, randomized controlled trial studied men 55-75 y of age. Subjects consumed 30 g protein from WPI or PB (25% soy, 25% whey, and 50% casein) 1 h after leg extension exercise (8 sets of 10 repetitions at 70% one-repetition maximum). Blood and muscle amino acid concentrations and basal and postexercise muscle protein turnover were measured by using stable isotopic methods. Muscle mTORC1 signaling was assessed by immunoblotting.

Results: Both groups increased amino acid concentrations (P < 0.05) and mTORC1 signaling after protein ingestion (P < 0.05). Postexercise fractional synthesis rate (FSR; P ≥ 0.05), fractional breakdown rate (FBR; P ≥ 0.05), and net balance (P = 0.08) did not differ between groups. WPI increased FSR by 67% (mean ± SEM: rest: 0.05% ± 0.01%; postexercise: 0.09% ± 0.01%; P < 0.05), decreased FBR by 46% (rest: 0.17% ± 0.01%; postexercise: 0.09% ± 0.03%; P < 0.05), and made net balance less negative (P < 0.05). PB ingestion did not increase FSR (rest: 0.07% ± 0.03%; postexercise: 0.09% ± 0.01%; P ≥ 0.05), tended to decrease FBR by 42% (rest: 0.25% ± 0.08%; postexercise: 0.15% ± 0.08%; P = 0.08), and made net balance less negative (P < 0.05). Within-group percentage of change differences were not different between groups for FSR, FBR, or net balance (P ≥ 0.05).

Conclusions: WPI and PB ingestion after exercise in older men induced similar responses in hyperaminoacidemia, mTORC1 signaling, muscle protein synthesis, and breakdown. These data add new evidence for the use of whey or soy-dairy PBs as targeted nutritional interventions to counteract sarcopenia. This trial was registered at clinicaltrials.gov as NCT01847261.

Keywords: aging; leucine; muscle protein turnover; protein supplementation; sarcopenia.

FIGURE 1

Consort flow diagram for study recruitment.

FIGURE 2

Changes from Rest in blood valine (A), muscle valine (B), blood isoleucine (C), muscle isoleucine (D), blood leucine (E), muscle leucine (F), blood phenylalanine (G), and muscle phenylalanine (H) in older men during the postexercise recovery period after ingestion of whey or protein blend 1 h after a bout of resistance exercise. Data are means ± SEMs, n = 10 (WPI) or 9 (PB). *Different from Rest within treatment group for muscle, P < 0.05. Line with asterisk denotes difference from Rest for all time points with no difference between treatment groups for blood, P < 0.05. Line with hash sign denotes difference between treatment groups for blood, P < 0.05. PB, soy-dairy protein blend; WPI, whey protein isolate.

FIGURE 3

Western blot analyses of mTORC1 (A) and mTORC1 downstream effector proteins: S6K1 (B), 4E-BP1 (C), and rpS6 (D), in older men during the treatment period after a bout of resistance exercise. Data are means ± SEMs, n = 10 (WPI) or 9 (PB). *Different from Rest, P < 0.05. ^#Different from 2 h Post, P < 0.05. There was no difference between groups at any time point. Two representative bands are displayed for each time point because all samples were run in duplicate. mTORC1, mechanistic target of rapamycin complex 1; PB, soy-dairy protein blend; Post, postingestion; rpS6, ribosomal protein S6; WPI, whey protein isolate; 4E-BP1, 4-E binding protein-1.

FIGURE 4

FSR in the vastus lateralis of older men at rest and during the treatment period after an acute bout of resistance exercise and ingestion of WPI or PB 1 h after exercise. Early is 0–2 h postingestion, Late is 2–4 h postingestion, and Entire is 0–4 h postingestion. Data are means ± SEMs, n = 10 (WPI) or 9 (PB). *Different from Rest (P < 0.05). ^#Different from PB at Rest, P < 0.05. FSR, fractional synthesis rate; PB, soy-dairy protein blend; WPI, whey protein isolate.