背景:2005年,医学研究所建议使用氮平衡(NB)以外的方法来确定蛋白质的需求量。从那以后,使用指示剂氨基酸氧化(IAAO)的蛋白质需求已经发表,并且高于NB。谷胱甘肽(GSH),半胱氨酸的三肽,谷氨酸,和甘氨酸,是一种主要的抗氧化剂,可用作蛋白质充足性的功能指标。
目的:测量红细胞GSH动力学的变化(分数和绝对合成速率,FSR和ASR)在健康成年人中摄入一系列蛋白质并高于目前的建议。
方法:16名健康成年人(8名男性和8名女性,在6种蛋白质摄入量中有4种在0.6至1.5g·kg-1·d-1范围内进行了25.6±0.9y(平均值±SEM)的研究。在适应每种蛋白质摄入2天之后,在输注[U-13C2-15N]甘氨酸7小时期间评估了红细胞GSH动力学。进行血液和尿液测试以测量氧化应激标志物,血浆同型半胱氨酸,甘油三酯,血浆氨基酸浓度,5-L-氧代脯氨酸(5-OP),和尿硫酸盐。使用R中的混合效应变化点回归确定最大化GSH合成的蛋白质摄入量。主要和次要结果使用线性混合效应和重复测量方差分析(ANOVA)与Tukey的事后检验进行分析。
结果:在78%·d-1时,使GSHFSR最大化的蛋白质摄入量为1.0g·kg-1·d-1(95%置信区间=0.63,1.39)。与1.5g·kg-1·d-1相比,GSHASR在0.6和0.8g·kg-1·d-1处显着降低(与3.71mmol·L-1·d-1相比为2.03和2.17)。增加蛋白质摄入导致尿硫酸盐增加,但不影响红细胞GSH浓度,血浆氧化应激标志物,甘油三酯,同型半胱氨酸,或5-OP。
结论:蛋白质摄入量为1.0g·kg-1·d-1使GSH合成最大化,这与早期IAAO衍生的蛋白质需求为0.93至1.2g·kg-1·d-1一致。这些发现表明,基于NB(0.66g·kg-1·d-1)的建议可能会低估蛋白质对足够健康的需求。
背景:#NCT02971046,https://clinicaltrials.gov/ct2/show/NCT02971046。
In 2005, the Institute of Medicine advised using methods other than nitrogen balance (NB) for determining protein requirements. Since then, protein requirements using indicator amino acid oxidation (IAAO) have been published and are higher than NB. Glutathione (GSH), a tripeptide of cysteine, glutamate, and glycine, is a principal antioxidant that can be used as a functional indicator of protein adequacy.
The aim of this study was to measure changes in erythrocyte GSH kinetics [fractional synthesis rate (FSR) and absolute synthesis rate (ASR)] in healthy adults following a range of protein intakes at and above the current recommendations.
Sixteen healthy adults [8 males and 8 females, aged 25.6 ± 0.9 y (mean ± SEM)] were studied at 4 of 6 protein intakes ranging from 0.6 to 1.5 g⋅kg-1⋅d-1. Erythrocyte GSH kinetics were assessed during a 7-h infusion of [U-13C2-15N]glycine following 2 d of adaptation to each protein intake. Blood and urine tests were performed to measure oxidative stress markers, plasma homocysteine, triglycerides, plasma amino acid concentrations, 5-L-oxoproline (5-OP), and urinary sulfate. The protein intake that maximized GSH synthesis was determined using mixed-effect change-point regression in R. Primary and secondary outcomes were analyzed using linear mixed-effects and repeated-measures analysis of variance with Tukey\'s post hoc test.
The protein intake that maximized GSH FSR at 78%⋅d-1 was 1.0 g⋅kg-1⋅d-1 (95% confidence interval: 0.63, 1.39). GSH ASR was significantly lower at 0.6 and 0.8 g⋅kg-1⋅d-1 than at 1.5 g⋅kg-1⋅d-1 (2.03 and 2.17, respectively, compared with 3.71 mmol⋅L-1⋅d-1). Increasing the protein intake led to increased urinary sulfate but did not affect erythrocyte GSH concentration, plasma oxidative stress markers, triglycerides, homocysteine, or 5-OP.
A protein intake of 1.0 g⋅kg-1⋅d-1 maximized GSH synthesis, which is in agreement with earlier IAAO-derived protein requirements of 0.93 to 1.2 g⋅kg-1⋅d-1. These findings suggest that recommendations based on NB (0.66 g⋅kg-1⋅d-1) may underestimate protein needs for adequate health. This trial was registered at clinicaltrials.gov as NCT02971046.