生酮飲食一開始不是用來減肥!營養學教授:生酮飲食的生理機制
在醫學一直進步時,肥胖仍然是全球關注之重要健康議題,全球約有 39% 的成人過重及肥胖,肥胖與糖尿病、高血壓、心血管疾病等耳熟能詳的慢性疾病息息相關,不健康的生活方式及不好的飲食習慣都與肥胖相關,而生酮飲食是一個近來非常流行的快速減肥的飲食型態。
「生酮飲食」一開始不是用來減肥的飲食型態
1921 年 Russel Wilder 發展出「生酮飲食」(ketogenic diet)此詞,使用生酮飲食來治療癲癇,在近十年來,生酮飲食一直做為小兒癲癇有效的飲食治療。近年來才被應用於減肥的飲食策略。由於癲癇歸咎於腦部神經元不正長的活動,酮體可抑制這些不正常的神經傳導物質,保護神經細胞,進而應用於癲癇的治療。癲癇是遺傳性的疾病,因兩種遺傳性基因缺陷導致葡萄糖載體蛋白(glucose transporter 1, GLUT1)和丙酮酸鹽脫氫酵素(pyruvate dehydrogenase)不足,使得腦細胞無法利用醣類,因此以酮體作為替代性的能量來源。
生酮飲食為高脂肪、低碳水化合物的飲食,而根據不同脂肪比例及脂肪酸碳鏈可以再細分 4 種生酮飲食(如下表)。嚴格的生酮飲食是脂肪比上非脂肪的克數比為 4:1~3:1,也就是 4 公克或 3 公克的脂肪搭配 1 公克的醣類加上蛋白質,臨床上執行非常不容易,但是為了治療癲癇發作,是必須的治療飲食。由於生酮飲食的脂肪比例極高、醣類極低,因此被阿金(Atkins)博士應用作為減重飲食,而降低了脂肪比例為 2:1~1:1。另外由於中鏈脂肪酸(MCT)的生酮效果較佳,因此也發展出含有 MCT 的生酮飲食。
飲食名稱 |
碳水化合物 |
蛋白質 |
脂質 |
||
生酮飲食 |
傳統型 |
1(g) |
: |
4(g) |
|
傳統型 |
1(g) |
: |
3(g) |
||
1(g) |
: |
2(g) |
|||
1(g) |
: |
1(g) |
|||
低升醣指數 |
1(g) |
: |
1(g) |
||
Modified Atkins (阿金飲食) |
1(g) 第一個月 10g,之後 15-20g |
: |
1(g) |
||
MCT型 |
19 |
10 |
60% MCT |
「生酮飲食」的生理機制
碳水化合物是人體產生能量的主要來源,當每天攝取量少於 50 公克時,會使體內缺乏碳水化合物,此時胰島素分泌會顯著減少,而身體會進入分解代謝狀態,經糖質新生作用或生酮作用產生能量給體內利用。
酮體為肝臟粒腺體脂肪酸氧化不完全的代謝中間物,其包括丙酮(acetone)、乙醯乙酸(acetoacetate)及β-羥基丁酸(β-hydroxybutyrate),且可做為能量來源。
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