肌酸跟蛋白粉到底对肾脏有没有影响？

『蛋白粉伤肾』是没有科学依据的，属于未经证实的谣言。因为蛋白质并不由肾脏排泄，肾脏排出的是尿素；而尿素是一种极易排出的小分子，排泄不产生负担 一、 蛋白粉/蛋白质不经肾脏排泄

现在网上有些人张口就是「蛋白粉伤肾」、「增加肾脏负担」之类的话。

我搞不懂的是，这都2022年了，怎么还会有这种观点呢？生理学告诉我们， 肾不会排出膳食蛋白质，肾排泄的是尿素：

这其实在我们之前的文章中解释过：

用图形表示，就是这样的：

也就是说，吃下去的蛋白质，只有 部分 用于供能，最后代谢为二氧化碳、水和尿素，后者从肾脏排出，哪来的蛋白质让肾脏过滤/排泄？以我对杠精的了解，它们又会编：「排出尿素也会增加肾脏负担」，所以我们接下来讲讲尿素。

二、尿素排泄对肾脏有负担吗？

尿素是一种无色无味的中性分极小子，总体上不影响血液酸碱性 ^{[9] [10] [11]} 。

尿素分子分非常小，具有很高水溶性的 ^[12] ，极易随体液排出体外。除了尿液，人类还通过汗液 ^[13] 、眼泪 ^[14] 、唾液 ^{[15] [16]} 和粪便 ^{[17] [18] [19]} 排出尿素。

注意， 尿素太容易排出体外，人反而要努力留住它， 因为它能调节渗透压，留下尿素可以留下很多水分，减少水分排泄，浓缩尿液 ^{[20] [21] [22] [23]} ，从而帮助我们生存；人挽留尿素靠尿素转运蛋白Urea Transporter ，简称UT。

UT有A、B等大类 ^[24] ，在肾脏、心脏、脑、睾丸、泌尿系统等组织中有较广泛的分布。UT-B在大脑中大量存在，因为大脑中也含有较多尿素 ^{[25] [26]} 。UT-A又分了多种，有A1、A2、A3等。UT-A1一般分布在肾髓内集合管（IMCD）细胞的顶端膜上，它们能我们快速吸收尿素。

尿素多了，渗透压上升，水分被回收 ^{[27] [28]} 、尿液浓缩。这在演化上也说得通，因为水是宝贵的生存资源。

不仅人类，许多其他哺乳动物也是如此，Bankir等人使用有基因特征的小鼠模型进行研究 ^[29] ，它们体内不能产生尿素转运蛋白B（UT-B）。进食高蛋白食物后，正常小鼠血液尿素水平提高了44%，而UTB缺陷小鼠的尿素浓度没有增加

为啥没增加？排泄出去了。

随饮食中蛋白质的比例从10%增加到40%，UT-B基因缺陷小鼠的尿素排泄量增加了 5倍 。多项类似研究也得到了类似结果 ^{[30] [31] [32]} ，支持Bankir等人的结论，证明了尿素具有「易排泄，难保留」的特性。

因此『肾脏排泄尿素有压力』，又是凭空编造的谣言。

三、乳制品蛋白能降低肾结石几率

有许多大型研究支持这样的观点，即乳制品蛋白质能降低肾结石发病率。

例如Pietro等人 ^[33] 对健康专业人员研究（42919人）、美国护士健康研究I（60128人）和护士健康研究II（90629人）的数据进行了分析，摄入奶制品蛋白导致结石风险降低26%。

注意，如果多摄入非乳制品动物蛋白，男性患肾结石的风险显著升高。

也就是说，乳制品和乳清蛋白粉与肉类的健康效果存在差异，肉类可能对肾结石有促进作用，而乳制品和乳清蛋白粉可能对肾结石有一定程度的保护作用。

扩展阅读

肉崽：力训研究所课程介绍

不健身直接吃蛋白粉会怎么样？

为什么减脂容易掉肌肉?

当代年轻人为什么尿酸会高？

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