Abstract
BackgroundThe effects of ingesting varying essential amino acid (EAA)/protein-containing food formats on protein kinetics during energy deficit are undetermined. Therefore, recommendations for EAA/protein food formats necessary to optimize both whole-body protein balance and muscle protein synthesis (MPS) during energy deficit are unknown. We measured protein kinetics after consuming iso-nitrogenous amounts of free-form essential amino acid-enriched whey (EAA + W; 34.7 g protein, 24 g EAA sourced from whey and free-form EAA), whey (WHEY; 34.7 g protein, 18.7 g EAA), or a mixed-macronutrient meal (MEAL; 34.7 g protein, 11.4 g EAA) after exercise during short-term energy deficit.MethodsTen adults (mean ± SD; 21 ± 4 y; 25.7 ± 1.7 kg/m2) completed a randomized, double-blind crossover study consisting of three, 5 d energy-deficit periods (− 30 ± 3% of total energy requirements), separated by 14 d. Whole-body protein synthesis (PS), breakdown (PB), and net balance (NET) were determined at rest and in response to combination exercise consisting of load carriage treadmill walking, deadlifts, and box step-ups at the end of each energy deficit using L-[2H5]-phenylalanine and L-[2H2]-tyrosine infusions. Treatments were ingested immediately post-exercise. Mixed-muscle protein synthesis (mixed-MPS) was measured during exercise through recovery.ResultsChange (Δ postabsorptive + exercise to postprandial + recovery [mean treatment difference (95%CI)]) in whole-body (g/180 min) PS was 15.8 (9.8, 21.9; P = 0.001) and 19.4 (14.8, 24.0; P = 0.001) greater for EAA + W than WHEY and MEAL, respectively, with no difference between WHEY and MEAL. ΔPB was − 6.3 (− 11.5, − 1.18; P = 0.02) greater for EAA + W than WHEY and − 7.7 (− 11.9, − 3.6; P = 0.002) greater for MEAL than WHEY, with no difference between EAA + W and MEAL. ΔNET was 22.1 (20.5, 23.8; P = 0.001) and 18.0 (16.5, 19.5; P = 0.00) greater for EAA + W than WHEY and MEAL, respectively, while ΔNET was 4.2 (2.7, 5.6; P = 0.001) greater for MEAL than WHEY. Mixed-MPS did not differ between treatments.ConclusionsWhile mixed-MPS was similar across treatments, combining free-form EAA with whey promotes greater whole-body net protein balance during energy deficit compared to iso-nitrogenous amounts of whey or a mixed-macronutrient meal.Trial registrationClinicalTrials.gov, Identifier no. NCT04004715. Retrospectively registered 28 June 2019, first enrollment 6 June 2019
Highlights
Military personnel, weight-class athletes, and workers in arduous occupations, such as wildland firefighters, regularly experience periods of unavoidable energy deficit, which can degrade skeletal muscle and increase wholebody protein loss due, in part, to sustained negative whole-body protein balance and blunted muscle protein synthesis (MPS) [1,2,3,4,5]
While mixed-MPS was similar across treatments, combining free-form essential amino acid (EAA) with whey promotes greater whole-body net protein balance during energy deficit compared to iso-nitrogenous amounts of whey or a mixed-macronutrient meal
The anabolic stimulus provided by mixed-macronutrient meals may be suboptimal during these scenarios because the amino acid composition (EAA content), digestion and absorption rates, and subsequent increase in peripheral EAA concentrations are lower after consuming mixed-macronutrient meals than intact protein alone or free-form EAA
Summary
Weight-class athletes, and workers in arduous occupations, such as wildland firefighters, regularly experience periods of unavoidable energy deficit, which can degrade skeletal muscle and increase wholebody protein loss due, in part, to sustained negative whole-body protein balance and blunted muscle protein synthesis (MPS) [1,2,3,4,5]. The food format of the EAA/protein consumed dictates its quality and anabolic stimulus due to its constituent amino acid composition and its digestibility and absorption kinetics. These factors influence the amount and pattern of EAA entering peripheral circulation and the substrate available to support whole-body protein turnover and MPS [10,11,12,13]. EAA ingested in free-form is another alternative to mixed-macronutrient meals, as it does not require digestion, is absorbed rapidly, and results in a rapid increase in peripheral EAA concentrations versus other EAA/protein food formats. Mixed-muscle protein synthesis (mixed-MPS) was measured during exercise through recovery
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