Effects of protein intake prior to carbohydrate-restricted endurance exercise: a randomized crossover trial

Abstract

Background: Deliberately training with reduced carbohydrate availability, a paradigm coined training low, has shown to promote adaptations associated with improved aerobic capacity. In this context researchers have proposed that protein may be ingested prior to training as a means to enhance the protein balance during exercise without spoiling the effect of the low carbohydrate availability. Accordingly, this is being practiced by world class athletes. However, the effect of protein intake on muscle protein metabolism during training low has not been studied. This study aimed to examine if protein intake prior to exercise with reduced carbohydrate stores benefits muscle protein metabolism in exercising and non-exercising muscles.

Methods: Nine well-trained subjects completed two trials in random order both of which included a high-intensity interval ergometer bike ride (day 1), a morning (day 2) steady state ride (90 min at 65% VO2peak, 90ss), and a 4-h recovery period. An experimental beverage was consumed before 90ss and contained either 0.5 g whey protein hydrolysate [WPH]/ kg lean body mass or flavored water [PLA]. A stable isotope infusion (L-[ring-13C6]-phenylalanine) combined with arterial-venous blood sampling, and plasma flow rate measurements were used to determine forearm protein turnover. Myofibrillar protein synthesis was determined from stable isotope incorporation into the vastus lateralis.

Results: Forearm protein net balance was not different from zero during 90ss exercise (nmol/100 ml/min, PLA: 0.5 ± 2.6; WPH: 1.8, ± 3.3) but negative during the 4 h recovery (nmol/100 ml/min, PLA: - 9.7 ± 4.6; WPH: - 8.7 ± 6.5); no interaction (P = 0.5) or main effect of beverage (P = 0.11) was observed. Vastus lateralis myofibrillar protein synthesis rates were increased during 90ss exercise (+ 0.02 ± 0.02%/h) and recovery (+ 0.02 ± 0.02%/h); no interaction (P = 0.3) or main effect of beverage (P = 0.3) was observed.

Conclusion: We conclude that protein ingestion prior to endurance exercise in the energy- and carbohydrate-restricted state does not increase myofibrillar protein synthesis or improve net protein balance in the exercising and non-exercising muscles, respectively, during and in the hours after exercise compared to ingestion of a non-caloric control.

Trial registration: clinicaltrials.gov, NCT01320449. Registered 10 May 2017 - Retrospectively registered, https://ichgcp.net/clinical-trials-registry/NCT03147001.

Keywords: Carbohydrate restriction; Dietary protein; Endurance training; Protein metabolism.

Conflict of interest statement

The study was funded in part by a research grants from Arla Foods Ingredients Group P/S. MSL and URM currently hold positions at Arla Foods Ingredients P/S as industrial PhD-student and research scientist, respectively. The views expressed in the manuscript are those of the authors and do not necessarily reflect the position or policy of Arla Foods Ingredients P/S, Denmark. The other authors have no conflict of interest.

Figures

Fig. 1

Overview of study design. On day 1, all meals were provided. At 1900 subjects commenced 10 × 5 min intervals at 82.5% (HIIT) of individual peak power output (PPO) on a customized ergometer bike. L-[ring-13C6-phenylalanine] was initiated during the night. Upon awakening (day 2), blood, muscle and urine samples were collected before commencement of a 90 min steady state ride (55% PPO). Subsequently subjects rested in a supine position for 4 h. Samples were collected as indicated

Fig. 2

Blood parameters. Change in hormone and metabolite levels during BL, 90ss and BR. Insulin (a), cortisol (b), glucose (c), free fatty acids (FFA) (d), 3-hydroxybutyrate (e), urea (f). Data are shown as means ± SD (n = 9); P < 0.05. Means within each trial with different subscripts are significantly different from each other; WPH subscripts are in cursive. # Significant difference between PLA and WPH at each respective timepoint

Fig. 3

Arterial concentrations of phenylalanine (a) and leucine (b) at baseline (BL), during 90 steady state exercise (90ss) and during bed rest recovery (BR) with PLA or WPH ingestion. Values are means ± SD (n = 9); P < 0.05. Means within each trial with different subscripts are significantly different from each other; WPH subscripts are in cursive. # Significant difference between PLA and WPH at each respective timepoint

Fig. 4

Arterial phenylalanine enrichment at baseline (BL), during 90 steady state exercise (90ss) and bed rest recovery (BR) with PLA or WPH ingestion. Values are means ± SD (n = 9); P < 0.05. Means within each trial with different subscripts are significantly different from each other; WPH subscripts are in cursive. # Significant difference between PLA and WPH at each respective timepoint

Fig. 5

Forearm plasma flow at baseline (BL), during 90 steady state exercise (90ss) and bed rest recovery (BR) with PLA or WPH ingestion. Values are means ± SD (n = 9); P < 0.05. Means within each trial with different subscripts are significantly different from each other; WPH subscripts are in cursive

Fig. 6

Forearm net protein balance (a), forearm protein synthesis (b), forearm protein breakdown (c) at baseline (BL), during 90 steady state exercise (90ss) and during bed rest recovery (BR) with PLA or WPH ingestion. Values are means ± SD (n = 9); P < 0.05. Means with different subscripts are significantly different from each other

Fig. 7

Muscle protein FSR of the m. vastus lateralis during baseline (BL), 90 min steady state exercise (90ss) and bed rest recovery (BR) with PLA or WPH ingestion. BL FSR’s were performed at Visit 1 regardless of treatment (hatched bars). Values are means ± SD (n = 9); P < 0.05. * Significantly different from BL

Fig. 8

Protein phosphorylation. Mammalian target of rapamycin (mTOR) (a), ribosomal protein S6 kinase beta-1 (p70S6K) (b), eukaryotic translation initiation factor 4E (EIF4E) (c), tumor protein p53 (p53) (d), p38 mitogen-activated protein kinases (p38MAPK) (e). Western blots representing the time-course effects are presented below the graphs. Based on the applied molecular standards, approximated molecular weights are indicated to the right. n = 9 for all timepoints. Values are normalized to PRE 90ss and are expressed as means ± SD; P < 0.05. * Significantly different from BL. # Significant difference between trials

Fig. 9

Gene expression. mRNA expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) (a), mRNA expression of mitochondrial transcription factor A (TFAM) (b), mRNA expression of cytochrome c oxidase subunit IV (COXIV) (c), mRNA expression of carnitine palmitoyl transferase 1B (CPT1B) (d). n = 9 for all timepoints. Values are set relative to PRE 90ss and the fold changes are expressed as means ± SD; P < 0.05. Means within each trial with different subscripts are significantly different from each other. # Significant difference between trials