Department of Sport and Health Sciences, College of Life and Environmental Science, University of Exeter, Exeter, UK.
University of Exeter Medical School, University of Exeter, Exeter, UK.
Am J Clin Nutr. 2021 Mar 11;113(3):548-561. doi: 10.1093/ajcn/nqaa136.
Short-term (<1 wk) muscle disuse lowers daily myofibrillar protein synthesis (MyoPS) rates resulting in muscle mass loss. The understanding of how daily dietary protein intake influences such muscle deconditioning requires further investigation.
To assess the influence of graded dietary protein intakes on daily MyoPS rates and the loss of muscle mass during 3 d of disuse.
Thirty-three healthy young men (aged 22 ± 1 y; BMI = 23 ± 1 kg/m2) initially consumed the same standardized diet for 5 d, providing 1.6 g protein/kg body mass/d. Thereafter, participants underwent a 3-d period of unilateral leg immobilization during which they were randomly assigned to 1 of 3 eucaloric diets containing relatively high, low, or no protein (HIGH: 1.6, LOW: 0.5, NO: 0.15 g protein/kg/d; n = 11 per group). One day prior to immobilization participants ingested 400 mL deuterated water (D2O) with 50-mL doses consumed daily thereafter. Prior to and immediately after immobilization upper leg bilateral MRI scans and vastus lateralis muscle biopsies were performed to measure quadriceps muscle volume and daily MyoPS rates, respectively.
Quadriceps muscle volume of the control legs remained unchanged throughout the experiment (P > 0.05). Immobilization led to 2.3 ± 0.4%, 2.7 ± 0.2%, and 2.0 ± 0.4% decreases in quadriceps muscle volume (P < 0.05) of the immobilized leg in the HIGH, LOW, and NO groups (P < 0.05), respectively, with no significant differences between groups (P > 0.05). D2O ingestion resulted in comparable plasma free [2H]-alanine enrichments during immobilization (∼2.5 mole percentage excess) across groups (P > 0.05). Daily MyoPS rates during immobilization were 30 ± 2% (HIGH), 26 ± 3% (LOW), and 27 ± 2% (NO) lower in the immobilized compared with the control leg, with no significant differences between groups (P > 0.05).
Three days of muscle disuse induces considerable declines in muscle mass and daily MyoPS rates. However, daily protein intake does not modulate any of these muscle deconditioning responses.Clinical trial registry number: NCT03797781.
短期（<1 周）肌肉废用会降低每日肌原纤维蛋白合成（MyoPS）率，导致肌肉质量损失。了解每日膳食蛋白质摄入量如何影响这种肌肉适应不良需要进一步研究。
评估分级膳食蛋白质摄入量对 3 天废用期间每日 MyoPS 率和肌肉质量损失的影响。
33 名健康年轻男性（年龄 22 ± 1 岁；BMI = 23 ± 1 kg/m2）最初连续 5 天摄入相同的标准化饮食，提供 1.6 g 蛋白质/kg 体重/d。此后，参与者经历了为期 3 天的单侧腿部固定期，在此期间，他们被随机分配到 3 种等热量饮食中的 1 种，其中含有相对较高、较低或不含蛋白质（HIGH：1.6、LOW：0.5、NO：0.15 g 蛋白质/kg/d；每组 11 人）。在固定前一天，参与者摄入 400 毫升氘化水（D2O），每天摄入 50 毫升剂量。在固定前和固定后立即进行大腿双侧 MRI 扫描和股外侧肌活检，分别测量股四头肌体积和每日 MyoPS 率。
对照腿的股四头肌体积在整个实验过程中保持不变（P > 0.05）。固定导致固定腿的股四头肌体积分别减少 2.3 ± 0.4%、2.7 ± 0.2%和 2.0 ± 0.4%（P < 0.05），HIGH、LOW 和 NO 组之间无显著差异（P > 0.05）。D2O 摄入导致各组固定期间血浆游离[2H]-丙氨酸富集相似（~2.5 摩尔百分比过剩）（P > 0.05）。固定期间，固定侧与对照侧相比，MyoPS 率分别降低 30 ± 2%（HIGH）、26 ± 3%（LOW）和 27 ± 2%（NO）（P < 0.05），组间无显著差异（P > 0.05）。
3 天的肌肉废用会导致肌肉质量和每日 MyoPS 率显著下降。然而，每日蛋白质摄入量不会调节任何这些肌肉适应不良的反应。
NCT03797781。
