L-Glutamine  左旋麩胺醯胺

生化效應：

保持腸道結構和功能；免疫功能上扮演一角色；參與血液循環胺基酸氮的輸送；生化壓力和敗血症時有支撐的角色。 

麩胺醯胺是人體含量最多的胺肌酸，肌肉和血液中一半的游離胺肌酸是麩胺醯胺。 為非必須胺肌酸，可由麩胺酸glutamic acid而來，主要在骨骼肌和肝臟中。

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麩胺醯胺在人體的主要功能是合成其他胺基酸的前趨物和免疫細胞、小腸和腎臟是麩胺醯胺的主要消耗處。 

臨床指引：

1.      酒癮：1g/day 可減少9/10患者的酒癮（雙盲研究）。 

2.      全靜脈營養（TPN）：加入麩胺醯胺可以預防腸黏膜的破壞（隨機研究）。 

3.      外科和危急病變：TPN中加入麩胺醯胺可以加速復原、降低死亡率和減少住院天數（雙盲研究）。 

4.      癌症化療：6g 每天3次可預防化療造成的腸胃道損傷（無控制組研究）。 

5.      加速恢復從強烈的體能運動：跑完馬拉松，立即加5g於水中飲用，2小時後再喝一杯，可以減少期後7天感染率（19.2%：51.2%）（雙盲研究）。 

6.      胃潰瘍：1.6g/day 可以加速潰瘍的癒合。 

劑量和給法：

雖然人體可以合成麩胺醯胺，但是生化壓力大時就不敷使用。

補充劑量 1-20g/day 或更多  分次服用。 

毒性：

一般耐受良好。40g/day x 12週 也不見明顯的副作用。 

·  Boosts immune system function 強化免疫功能

·  Maintains muscle mass 保持肌肉

·  Prevents muscle catabolism (breakdown) 預防肌肉減少

·  Enhances glycogen storage 增加肝醣

·  Aids recovery from exercise 幫助運動恢復

劇烈的運動訓練會導致血漿麩醯胺酸水平明顯下降。 長期較低的麩醯胺酸水平被認為是導致運動過度訓練症候群以及短暫的免疫抑制和感染風險增加的可能因素，這些因素通常會在激烈的訓練和比賽中影響競技運動員。 在代謝壓力的情況下，身體對麩醯胺酸的需求可能超過其產生足夠水平的能力——這意味著需要飲食來源來防止骨骼肌的分解代謝——骨骼肌是體內儲存麩醯胺酸的主要來源。

大量科學文獻支持補充麩醯胺酸對維持重症患者以及從大面積燒傷和大手術中恢復的患者的肌肉質量和免疫系統功能的有益作用。 當血漿麩醯胺酸水平下降時，骨骼肌可能進入分解代謝狀態，其中肌肉蛋白質被降解，為身體的其他部分提供遊離的麩醯胺酸。 由於骨骼肌是麩醯胺酸的主要來源（飲食除外），血漿麩醯胺酸的長期缺乏會導致骨骼肌蛋白和肌肉質量的顯著損失。 然而，針對當今市場上大多數商業生產的麩醯胺酸補充劑的主要目標族群——競技運動員，我們幾乎沒有做任何具體的工作。 近年來，至少有六項關於運動員補充麩醯胺酸的研究，並且為麩醯胺酸補充劑在運動族群中的功效奠定了堅實的基礎。 例如，麩醯胺酸在免疫系統支持中的作用已被證明可以預防劇烈體力活動後的感染——這往往會降低血漿麩醯胺酸水平。 麩醯胺酸補充劑也被證明可以在抵消皮質醇等壓力荷爾蒙的分解代謝（肌肉萎縮）影響方面發揮作用，皮質醇通常會因劇烈運動而升高。 麩醯胺酸刺激肝醣合成酶的功能，肝醣合成酶控制肌肉和肝臟中肝醣燃料儲存的合成和儲存，可能提供麩醯胺酸補充劑促進增強燃料儲存的機制。 麩醯胺酸補充劑會導致細胞麩醯胺酸水平和肌肉中麩醯胺酸儲存迅速上升。 麩醯胺酸也被認為可以增加細胞體積，從而刺激肝臟和肌肉中參與肝醣儲存以及參與蛋白質合成等合成代謝活動的酵素的活性。 麩醯胺酸補充劑也被假設可以增加生長激素的水平，這可能有助於刺激蛋白質合成並促進肌肉質量和力量的增加，但臨床研究尚未證明麩醯胺酸補充劑的這種作用的可靠證據。

每天至少 20 克的麩醯胺酸補充劑的耐受性良好，每天攝取 40 克的麩醯胺酸補充劑除了輕微胃腸道不適外，不會產生明顯的副作用。 與任何分離的氨基酸補充劑一樣，全天分 2-4 次服用可以增加全身儲存量，而不會造成明顯的吸收問題。

與其他胺基酸補充劑相比，麩醯胺酸補充劑相對便宜。 對於任何承受較高壓力的人，例如從受傷、手術或劇烈運動中恢復的人來說，麩醯胺酸補充劑是促進組織修復、減少肌肉分解代謝和幫助預防感染的經濟方法。

對於大多數運動員感興趣的免疫系統支持和抗分解代謝作用，建議劑量範圍為 1-10 克。

Intense exercise training results in a well-described drop in plasma glutamine levels. Chronically low glutamine levels have been implicated as a possible contributing factor in athletic overtraining syndrome as well as the transient immunosuppression and increased risk of infections that typically affects competitive athletes during intense training and competition. Under conditions of metabolic stress, the body’s need for glutamine may exceed its ability to produce adequate levels – meaning that a dietary source is required to prevent catabolism of skeletal muscle – the primary source of stored glutamine in the body.  

A significant body of scientific literature exists to support the beneficial effects of glutamine supplementation in maintaining muscle mass and immune system function in critically ill patients and in those recovering from extensive burns and major surgery. When plasma glutamine levels fall, skeletal muscles may enter a state of catabolism in which muscle protein is degraded to provide free glutamine for the rest of the body. Since skeletal muscle is the major source of glutamine (other than the diet), prolonged deficits in plasma glutamine can lead to a significant loss of skeletal muscle protein and muscle mass. Very little specific work has been done, however, to address the primary target population for the majority of commercially produced glutamine supplements on the market today – competitive athletes. In recent years, at least a half-dozen studies have been conducted on glutamine supplementation in athletes and a strong basis exists for the efficacy of glutamine supplements in athletic populations. For example, glutamine’s role in immune system support has been shown to prevent infections following intense bouts of physical activity – which tend to reduce plasma glutamine levels. Glutamine supplements have also been shown to play a role in counteracting the catabolic (muscle-wasting) effects of stress hormones such as cortisol, which are typically elevated by strenuous exercise. The function of glutamine in stimulating glycogen synthase, the enzyme which controls the synthesis and storage of glycogen fuel storage in muscles and liver, may provide a mechanism by which glutamine supplements promote enhanced fuel stores. Glutamine supplements cause a rapid rise in cellular glutamine levels and glutamine stores in muscle. Glutamine is also thought to increase cell volume, where it may stimulate the activity of enzymes in the liver and muscles involved in glycogen storage as well as those involved in anabolic activities such as protein synthesis. Glutamine supplements have also been hypothesized to increase levels of growth hormone, which may be expected to help stimulate protein synthesis and encourage gains in muscle mass and strength, but reliable evidence for this effect of glutamine supplements has not been demonstrated by clinical studies.  

Glutamine supplements are well tolerated at levels up to at least 20 grams per day and intakes of as much as 40 grams per day should induce no significant adverse effects outside of mild gastrointestinal discomfort. As with any isolated amino acid supplement, consumption in divided 2-4 divided doses throughout the day should increase total body stores without posing significant absorption issues.  

Glutamine supplements are relatively inexpensive compared to other amino acid supplements. For anybody exposed to heightened levels of stress, such as those recovering from injury, surgery, or intense exercise, glutamine supplements represent an economical way to promote tissue repair, reduce muscle catabolism and help prevent infections.  

For the immune system support and anti-catabolic actions that are of interest to most athletes, recommended doses range from 1-10 grams.