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Low-Carbohydrate Training Increases Protein Requirements of Endurance Athletes.

INTRODUCTION
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.


METHODS
Eight endurance-trained males (27±4y, 75±10kg, 67±10ml·kg body mass·min) 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 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). In the high-CHO availability trial (HIGH), participants consumed 3g CHO·kgduring the day before HIIT, and consumed 5g CHO·kgthat 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 (HIGH). Whole-body phenylalanine flux (PheRa) and oxidation (PheOx) were determined over 8h of recovery via oral [C]phenylalanine ingestion, according to standard indicator amino acid oxidation methodology, while consuming sufficient energy, 7.8g CHO·kg·d, and suboptimal protein (0.93g·kg·d).


RESULTS
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, 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·h, p<0.05), suggesting a greater amino acid requirement to support rates of whole-body protein synthesis.


CONCLUSION
Our findings suggest that performing endurance exercise with low-CHO availability increases protein requirements of endurance athletes.