Department of Kinesiology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
PepsiCo R&D Nutrition, Barrington, IL.
J Nutr. 2018 Jul 1;148(7):1088-1095. doi: 10.1093/jn/nxy091.
Older adults show a blunted muscle protein synthesis (MPS) response to postprandial hyperaminoacidemia relative to younger adults. Evidence suggests that this anabolic resistance can be overcome by consuming greater quantities of leucine.
The purpose of this trial was to determine whether the addition of leucine to a smaller dose (10 g) of milk proteins would, when compared with a larger dose (25 g) of whey protein isolate (WPI), result in similar increases in acute (hourly) and integrated (daily) myofibrillar protein synthesis (myoPS).
Healthy older (mean ± SD age: 69 ± 1 y) women (n = 11/group) were randomly assigned with the use of a single-blind, parallel-group design to twice-daily consumption of either WPI [25 g WPI (3 g l-leucine)] or leucine (LEU; 10 g milk protein with 3 g total l-leucine) for 6 d. Participants performed unilateral resistance exercise to allow assessment of the impact of the supplement alone and with resistance exercise. We determined acute (13C6-phenylanine) and integrated [using deuterated water (D2O)] rates of myoPS in the fasting (acute), basal (integrated), nonexercised, and exercised states.
Acute myoPS increased in both legs in response to LEU (fed: 45%; fed+exercise: 71%; P < 0.001) and WPI (fed: 29%; fed+exercise: 47%; P < 0.001) compared with fasting; the increase was greater with LEU than with WPI in the exercised leg (46%; P = 0.04) but not in the rested leg (P = 0.07). The acute myoPS response was greater in the exercised leg than in the rested leg for both WPI (63%) and LEU (58%) (P < 0.001). Integrated myoPS increased with WPI and LEU in the exercised leg (both 9%; P < 0.001) during supplementation, and with WPI (3%; P = 0.02) but not LEU (2%, P = 0.1) in the rested leg compared with the basal state.
A lower-protein (10 compared with 25 g/dose), leucine-matched beverage induced similar increases in acute and integrated myoPS in healthy older women. Lower-protein supplements with added leucine may represent an advantageous approach in older adults to maintain skeletal muscle anabolic sensitivity and attenuate muscle loss; however, further work is needed using longer-term interventions to substantiate these findings. This trial was registered at www.clinicaltrials.gov as NCT02282566.
与年轻人相比，老年人在餐后高氨基酸血症时肌肉蛋白质合成（MPS）的反应较为迟钝。有证据表明，通过摄入更多的亮氨酸可以克服这种合成代谢抵抗。
本试验旨在确定与乳蛋白的较大剂量（25 克乳清蛋白分离物[WPI]）相比，向较小剂量（10 克）的牛奶蛋白中添加亮氨酸是否会导致急性（每小时）和综合（每日）肌原纤维蛋白合成（myoPS）的增加相似。
健康的老年（平均年龄±标准差：69±1 岁）女性（每组 n=11）采用单盲、平行组设计，随机分为两组，每天两次分别摄入 WPI[25 克 WPI（3 克亮氨酸）]或亮氨酸（LEU；10 克牛奶蛋白，含 3 克总亮氨酸），共 6 天。参与者进行单侧抗阻运动，以评估补充剂单独和与抗阻运动结合的效果。我们测定了空腹（急性）、基础（综合）、非运动和运动状态下 13C6-苯丙氨酸的急性（13C6-苯丙氨酸）和综合[使用氘水（D2O）]myoPS 率。
LEU（fed：45%；fed+exercise：71%；P<0.001）和 WPI（fed：29%；fed+exercise：47%；P<0.001）均使两条腿的急性 myoPS 在进食后增加，与空腹相比；与 WPI 相比，LEU 在运动腿中的增加更大（46%；P=0.04），但在休息腿中没有差异（P=0.07）。两条腿的急性 myoPS 反应均随 WPI（63%）和 LEU（58%）（P<0.001）在运动腿中增加。补充期间，WPI 和 LEU 均使运动腿中的综合 myoPS 增加（均为 9%；P<0.001），而 WPI（3%；P=0.02）但 LEU（2%；P=0.1）在休息腿中的增加与基础状态相比无差异。
与每天 25 克相比，摄入较低剂量（10 克/剂量）、含亮氨酸的匹配饮料可使健康老年女性的急性和综合 myoPS 增加相似。添加亮氨酸的低蛋白补充剂可能是一种有利于维持老年人骨骼肌合成代谢敏感性和减少肌肉损失的方法；然而，还需要使用更长期的干预措施来证实这些发现。本试验在 www.clinicaltrials.gov 注册为 NCT02282566。
