肌酸跟蛋白粉到底對腎臟有沒有影響？

『蛋白粉傷腎』是沒有科學依據的，屬於未經證實的謠言。因為蛋白質並不由腎臟排泄，腎臟排出的是尿素；而尿素是一種極易排出的小分子，排泄不產生負擔 一、 蛋白粉/蛋白質不經腎臟排泄

現在網上有些人張口就是「蛋白粉傷腎」、「增加腎臟負擔」之類的話。

我搞不懂的是，這都2022年了，怎麽還會有這種觀點呢？生理學告訴我們， 腎不會排出膳食蛋白質，腎排泄的是尿素：

這其實在我們之前的文章中解釋過：

用圖形表示，就是這樣的：

也就是說，吃下去的蛋白質，只有 部份 用於供能，最後代謝為二氧化碳、水和尿素，後者從腎臟排出，哪來的蛋白質讓腎臟過濾/排泄？以我對杠精的了解，它們又會編：「排出尿素也會增加腎臟負擔」，所以我們接下來講講尿素。

二、尿素排泄對腎臟有負擔嗎？

尿素是一種無色無味的中性分極小子，總體上不影響血液酸堿性 ^{[9] [10] [11]} 。

尿素分子分非常小，具有很高水溶性的 ^[12] ，極易隨體液排出體外。除了尿液，人類還透過汗液 ^[13] 、眼淚 ^[14] 、唾液 ^{[15] [16]} 和糞便 ^{[17] [18] [19]} 排出尿素。

註意， 尿素太容易排出體外，人反而要努力留住它， 因為它能調節滲透壓，留下尿素可以留下很多水分，減少水分排泄，濃縮尿液 ^{[20] [21] [22] [23]} ，從而幫助我們生存；人挽留尿素靠尿素轉運蛋白Urea Transporter ，簡稱UT。

UT有A、B等大類 ^[24] ，在腎臟、心臟、腦、睪丸、泌尿系統等組織中有較廣泛的分布。UT-B在大腦中大量存在，因為大腦中也含有較多尿素 ^{[25] [26]} 。UT-A又分了多種，有A1、A2、A3等。UT-A1一般分布在腎髓內集合管（IMCD）細胞的頂端膜上，它們能我們快速吸收尿素。

尿素多了，滲透壓上升，水分被回收 ^{[27] [28]} 、尿液濃縮。這在演化上也說得通，因為水是寶貴的生存資源。

不僅人類，許多其他哺乳動物也是如此，Bankir等人使用有基因特征的小鼠模型進行研究 ^[29] ，它們體內不能產生尿素轉運蛋白B（UT-B）。進食高蛋白食物後，正常小鼠血液尿素水平提高了44%，而UTB缺陷小鼠的尿素濃度沒有增加

為啥沒增加？排泄出去了。

隨飲食中蛋白質的比例從10%增加到40%，UT-B基因缺陷小鼠的尿素排泄量增加了 5倍 。多項類似研究也得到了類似結果 ^{[30] [31] [32]} ，支持Bankir等人的結論，證明了尿素具有「易排泄，難保留」的特性。

因此『腎臟排泄尿素有壓力』，又是憑空編造的謠言。

三、乳制品蛋白能降低腎結石機率

有許多大型研究支持這樣的觀點，即乳制品蛋白質能降低腎結石發病率。

例如Pietro等人 ^[33] 對健康專業人員研究（42919人）、美國護士健康研究I（60128人）和護士健康研究II（90629人）的數據進行了分析，攝入奶制品蛋白導致結石風險降低26%。

註意，如果多攝入非乳制品動物蛋白，男性患腎結石的風險顯著升高。

也就是說，乳制品和乳清蛋白粉與肉類的健康效果存在差異，肉類可能對腎結石有促進作用，而乳制品和乳清蛋白粉可能對腎結石有一定程度的保護作用。

擴充套件閱讀

肉崽：力訓研究所課程介紹

不健身直接吃蛋白粉會怎麽樣？

為什麽減脂容易掉肌肉?

當代年輕人為什麽尿酸會高？

參考

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