Training with low-carbohydrate (CHO) availability enhances markers of aerobic adaptation and has become popular to periodize throughout an endurance-training program. However, exercise-induced amino acid oxidation is increased with low muscle glycogen, which may limit substrate availability for post-exercise protein synthesis. We aimed to determine the impact of training with low-CHO availability on estimates of dietary protein requirements.
Eight endurance-trained males (27±4y, 75±10kg, 67±10ml·kg body mass-1·min-1) completed two trials matched for energy and macronutrient composition but with differing CHO periodization. In the low-CHO availability trial (LOW), participants consumed 7.8g CHO·kg-1 prior to evening high-intensity interval training (HIIT; 10 x 5 min at 10-km race pace, 1 min rest) and subsequently withheld CHO post-exercise (0.2g·kg-1). In the high-CHO availability trial (HIGH), participants consumed 3g CHO·kg-1during the day before HIIT, and consumed 5g CHO·kg-1that evening to promote muscle glycogen resynthesis. A 10km run (~80% HRmax) was performed the following morning, fasted (LOW) or 1h after consuming 1.2g CHO·kg-1 (HIGH). Whole-body phenylalanine flux (PheRa) and oxidation (PheOx) were determined over 8h of recovery via oral [13C]phenylalanine ingestion, according to standard indicator amino acid oxidation methodology, while consuming sufficient energy, 7.8g CHO·kg-1·d-1, and suboptimal protein (0.93g·kg-1·d-1).
Fat oxidation (indirect calorimetry) during the 10-km run was higher in LOW compared to HIGH (0.99±0.35 vs. 0.60±0.26 g·min-1, p<0.05). PheRa during recovery was not different between trials (p>0.05) whereas PheOX (reciprocal of protein synthesis) was higher in LOW compared to HIGH (8.8±2.7 vs. 7.9±2.4 umol·kg-1·h-1, p<0.05), suggesting a greater amino acid requirement to support rates of whole-body protein synthesis.
Our findings suggest that performing endurance exercise with low-CHO availability increases protein requirements of endurance athletes.
Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, ON, Canada
Address for Correspondence: Daniel R. Moore, Assistant Professor, Faculty of Kinesiology and Physical Education, University of Toronto, 100 Devonshire Place Toronto, ON M5S 2C9, CANADA, Tel:416-946-4088, Email: email@example.com
This study was supported by grants to DRM from Ajinomoto Innovation Alliance Program, Canadian Foundations for Innovation and Ontario Research Fund. JBG held a Canadian Institutes of Health Research Postdoctoral Fellowship. The results of this study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. The results of the present study do not constitute endorsement by ACSM. The authors report no conflicts of interest.
Accepted for Publication: 6 May 2019