Research Institute, The Hospital for Sick Children, Toronto, Canada.
Am J Clin Nutr. 2012 Oct;96(4):759-67. doi: 10.3945/ajcn.111.024471. Epub 2012 Sep 5.
Leucine has been suggested to improve athletic performance. Therefore, the branched-chain amino acids (BCAAs), especially leucine, are popular as dietary supplements in strength-training athletes; however, the intake of leucine in excess of requirements raises concerns regarding adverse effects. Currently, the tolerable upper intake level (UL) for leucine is unknown.
The objective of the current study was to determine the UL for leucine in adult men under acute dietary conditions.
Five healthy adults (20-35 y) each received graded stepwise increases in leucine intakes of 50, 150, 250, 500, 750, 1000, and 1250 mg · kg⁻¹ · d⁻¹, which corresponded to the Estimated Average Requirement (EAR) and the EAR ×3, ×5, ×10, ×15, ×20, and ×25 in a total of 29 studies. The UL of leucine was identified by the measurement of plasma and urinary biochemical variables and changes in leucine oxidation by using l-[1-¹³C]-leucine.
A significant increase in blood ammonia concentrations above normal values, plasma leucine concentrations, and urinary leucine excretion were observed with leucine intakes >500 mg · kg⁻¹ · d⁻¹. The oxidation of l-[1-¹³C]-leucine expressed as label tracer oxidation in breath (F¹³CO₂), leucine oxidation, and α-ketoisocaproic acid (KIC) oxidation led to different results: a plateau in F¹³CO₂ observed after 500 mg · kg⁻¹ · d⁻¹, no clear plateau observed in leucine oxidation, and KIC oxidation appearing to plateau after 750 mg · kg⁻¹ · d⁻¹.
On the basis of plasma and urinary variables, the UL for leucine in healthy adult men can be suggested at 500 mg · kg⁻¹ · d⁻¹ or ~35 g/d as a cautious estimate under acute dietary conditions.
亮氨酸被认为可以提高运动表现。因此，支链氨基酸（BCAAs），尤其是亮氨酸，作为一种膳食补充剂在力量训练运动员中很受欢迎；然而，亮氨酸的摄入量超过需求会引起对不良反应的担忧。目前，亮氨酸的可耐受最高摄入量（UL）尚不清楚。
本研究旨在确定健康男性在急性饮食条件下亮氨酸的 UL。
5 名健康成年人（20-35 岁）每人分别接受 50、150、250、500、750、1000 和 1250mg·kg⁻¹·d⁻¹的亮氨酸逐渐递增摄入量，这相当于 29 项研究中的估计平均需求量（EAR）和 EAR×3、×5、×10、×15、×20 和×25。通过测量血浆和尿液生化变量以及使用 l-[1-¹³C]-亮氨酸测定亮氨酸氧化的变化来确定亮氨酸的 UL。
亮氨酸摄入量>500mg·kg⁻¹·d⁻¹时，血液氨浓度显著高于正常值，血浆亮氨酸浓度和尿亮氨酸排泄量增加。l-[1-¹³C]-亮氨酸的氧化表示为呼气中的示踪剂氧化（F¹³CO₂）、亮氨酸氧化和α-酮异己酸（KIC）氧化得出了不同的结果：F¹³CO₂在 500mg·kg⁻¹·d⁻¹后出现平台，亮氨酸氧化没有明显的平台，而 KIC 氧化在 750mg·kg⁻¹·d⁻¹后似乎出现平台。
根据血浆和尿液变量，健康成年男性亮氨酸的 UL 可在 500mg·kg⁻¹·d⁻¹或约 35g/d 时谨慎估计，这是在急性饮食条件下的估计值。
