你可能想不到最常見蔬食中就含有8種必需氨基酸

編譯者前言：本來不想把文章弄的太長、太複雜，但後來想了下，還是盡量講清楚比較好，因為人們長期以來被灌輸了太多對植物蛋白質的觀點，已經形成了「成見」，而打破「成見」是一個困難和複雜的過程。

您如果覺得太複雜，只需要看那張8種必需氨基酸含量表。

蛋白質的質量和數量

On Protein Quality and Quantity

（1）蛋白質的分類

（1）Protein Classifications

1914年，研究人員在研究試驗室老鼠蛋白質需求時發現老鼠吃動物蛋白比吃植物蛋白要生長的更快速。其它研究也產生了同樣的結果。

In 1914, researchers studying the protein requirements of laboratory rats reported that rats grew more rapidly on animal-based proteins than on plant-based proteins. Other studies yielded the same results.

當時，針對人類的蛋白質和氨基酸的需要尚不清楚，但科學家質疑植物性食物可能不支持老鼠的正常生長（或者也延伸到人類），因為植物性食物不包含足夠量的特定種類氨基酸。

At the time, the protein and amino acid requirements for humans were unknown, but scientists suspected that vegetable foods might not support normal growth in rats (or by extension, humans) because they did not contain sufficient amounts of certain amino acids.

動物性食物（肉、蛋、奶）因此被劃分為「A類」蛋白質來源，而植物性食物（蔬菜和水果）則被看作劣等的，或者「B類」蛋白質來源。

Animal foods (dairy, meat, and eggs) were thus classified as "Class A" protein sources, while plant foods (vegetables and fruits) came to be seen as inferior, or "Class B" proteins.

動物性食物 即 所謂的 「A 類」 蛋白質來源：

植物性食物 即 所謂的 「B類」 蛋白質來源：

（2）「高品質」的含義

（2）The Meaning of "High Quality"

所有動物必須持續補充身體中的蛋白質，從食物中攝取的蛋白質提供身體蛋白質合成所需的氨基酸。

All animals must continuously replenish their proteins, and the protein they take in through food provides the amino acids necessary for protein synthesis.

在所攝取的食物中每種氨基酸比例與攝食者體內每種氨基酸比例越接近，攝食者利用食物合成蛋白質的效率則越高。

The more closely the ratios of individual amino acids in a given food match the ratios of individual amino acids in the eater, the more efficiently that eater will use the food to synthesize protein.

動物與其它動物之間的氨基酸比例比動物與植物之間的氨基酸比例更類似。因此，人類和其它動物利用所有動物性蛋白質的效率要超過所有植物性蛋白質。

Animals』 amino acid ratios resemble the amino acid ratios of other animals much more closely than the amino acid ratios of plants. Therefore, humans and other animals utilize all animal-based proteins more efficiently than all plant-based proteins.

因此，動物性蛋白質被說成是有更高的生物價值，一直被描述成「高品質」蛋白質。

As a result, animal-based proteins are said to have higherbiological value,and have been described as "high-quality" proteins.

從嚴格的科學觀點來看，高價值、高品質蛋白質就單單是指能促進身體更有效率地合成蛋白質（因此細胞分裂和身體成長也更有效率）。

From a strictly scientific perspective, ahigh-value,high-qualityprotein is simply one that tends to promote more efficient protein synthesis (and therefore more efficient cell division and body growth.)

但是，這個術語暗指這類蛋白質是優越的—確實科學家使用這樣的語言，因為他們假定這些蛋白質更優越。從消費者視角來看，當然更喜歡高價值、高品質的食物。但動物蛋白真的是更優越嗎？

However, this terminology implies that such a protein is superior—and indeed scientists used this language because they assumed these proteins tobesuperior. From a consumer perspective，high-value, high-qualityfoods certainly sound preferable. But are they really?

（3）重新思考植物蛋白質的「問題」

（3）Rethinking the "Problem" with Plant Proteins

早期科學家並不知道蛋白質的高效利用率對人類來說並非是必然有利的。

Unbeknownst to early scientists, efficient protein utilization is not necessarily advantageous for humans.

因為事實證明，「高品質」蛋白質也傾向於促進非期望的（例如癌細胞和動脈粥樣硬化組織）高效率生長。

As it turns out, "high-quality" proteins also tend to promoteundesirablegrowth (such as that of cancer cells and atherogenic tissue) quite efficiently.

相比之下，植物蛋白的氨基酸組成—總是跟我們的有點不匹配—對促進非預期生長也是一樣較低效率。然而，科學家還沒有領會蛋白質與疾病之間的這種關係。

By contrast, the amino acid compositions of plant proteins—always a bit of a mismatch with ours—are also less efficient at promoting unwanted growth. However, scientists were not able to intuit this relationship between protein and disease.

植物性食物具有「較低品質」的觀點是因為它們提供的是「不完全」蛋白質（即蛋白質缺少某些特定的氨基酸），這造成很多人的憂慮，包括Frances Moore Lappe（拉佩），在她1971年出版的書《一座小行星的飲食方式》中將「蛋白質補充」的想法普及。

The idea that plant foods were "lower quality" because they provided "incomplete" proteins (i.e., proteins deficient in certain amino acids) concerned many people, including Frances Moore Lappe, who popularized the idea of "protein complementing" in her 1971 book,Diet for a Small Planet.

Lappe（拉佩），一位推廣素食以解決世界飢餓問題的社會學家，分享了早期科學家對植物蛋白質的顧慮。她得出結論（就像很多其他人一樣）素食只有在吃了特定的包括所有必需氨基酸組合的情況下才是健康的。這種想法深深地植入了我們對蛋白質的共同想法—但事實並非如此。

Lappe, a sociologist promoting a vegetarian diet as a solution to world hunger, shared early scientists" concerns about plant proteins. She concluded (as did many others) that vegetarians could only be healthy if they ate particular plant foods in combinations that provided all the essential amino acids. The idea became entrenched in our common thinking about protein—but it wasn』t valid.

（4）植物與氨基酸

（4）Plants and Amino Acids

科學家現在明白了植物性食物確實含有所有必需氨基酸。

Scientists now understand that plant foodsdocontain all the essential amino acids.

請注意一些普通的植物性食物中氨基酸含量與世界衛生組織（WHO）所推薦量的比較：

Note how the amino acid contents of some common plant foods compare with World Health Organization (WHO) recommendations:

譯註：圖中只有糙米的賴氨酸（Lys）和總蛋白質含量比WHO推薦量稍低。

世界衛生組織（WHO）得出的結論是只要吃了足夠熱量，「很少會有天然食物不能提供足夠必需氨基酸的情況，」 評論如下：

The World Health Organization (WHO) concludes that as long as they are high enough in calories, "few natural diets provide insufficient amounts of indispensable amino acids," commenting:

「必需氨基酸確實存在於豆類、根莖類和穀類中，總的來說含量遠超過推薦需求量，對於單一氨基酸有兩個例外。第一，存在於木薯和紅薯中的賴氨酸剛剛超過90%推薦需要量，而在穀類中的賴氨酸則介於57%至86%之間的推薦需要量…鑒於確認賴氨酸需求量的安全值存在不確定性，很明顯這方面需要更多的研究。」

"Clearly the content of indispensable amino acids in […] legumes, root crops and cereals is considerably greater than the proposed requirement values overall, and for each individual amino acid, with two exceptions. First, lysine is present in cassava and yam at just over 90% and in cereals at between 57% and 86% of requirement levels…Given the uncertainty which exists in identifying a secure value for the lysine requirement, it is clear that more work is required in this area."

即使穀物和木薯在有些實驗室研究中理論上有輕微的「不足」，也許對人類健康會造成問題，如果我們吃不同種類的全蔬食並攝取足夠的熱量，限制「垃圾食品」和精製食物的話，這個問題是非常容易解決的。

Even if the very slight theoretical "deficiencies" in grains and cassava observed in some lab studies could be problematic for human health, the issue is easily addressed if we consume sufficient calories of avariedwhole food, plant-based diet, limiting "junk" and refined foods.

換句話說，植物蛋白被稱為「不完全」是因為跟我們人類氨基酸圖譜不匹配，但在滿足飲食需要方面它們並非「不完全」。

In other words,plant proteins are referred to as "incomplete" because they do not match our human amino acid profile, but they are not "incomplete" when it comes to fulfilling our dietary needs.

同樣地，術語「低質量」意為植物蛋白比動物蛋白使用起來有些低效率；然而，對人類健康來說低質量的說法則意味著誤導。

Likewise, the terminology "lower quality" means that plant proteins are used somewhat less efficiently than animal proteins; however, the implication of inferiority for human health is misleading.

蛋白質「補充」是沒有必要的。

Protein "complementing" is unnecessary.

Lappe（拉佩）是同意的。在《一座小行星的飲食方式》後來的版本中，她糾正了最初對蛋白質補充的看法，她寫道：

Lappe agrees. In later editions ofDiet for a Small Planet, she reversed her initial views on protein complementing, writing:

「在1971版本中我強調了蛋白質互補性，因為我假定唯一獲得足夠蛋白質的方法…是創造一種能像動物蛋白一樣被人體利用的蛋白質。在對抗吃肉是唯一獲得高質量蛋白質的神話時，我卻製造了另一種神話。我給大眾造成了一種印象，要想不吃肉而獲得足夠蛋白質就必須非常小心地選擇食物。實際上，這遠比我想像的容易。」

"In 1971 I stressed protein complementarity because I assumed that the only way to get enough protein…was to create a protein as usable by the body as animal protein. In combating the myth that meat is the only way to get high-quality protein, I reinforced another myth. I gave the impression that in order to get enough protein without meat, considerable care was needed in choosing foods. Actually, it is much easier than I thought."

她補充道：

She adds:

「有三個重要例外，植物性飲食極少造成蛋白質缺乏。三種例外情況是飲食嚴重依賴[1]水果[2]有些根莖類食物，比如紅薯或木薯，或者[3]垃圾食品（精製麵粉，糖和油）。幸運的是，相對來講世界上很少有人試圖基本依賴這些食物作為單一熱量來源為生。在其它各種飲食中，如果人們攝取了足夠的熱量，他們幾乎肯定能獲得足夠的蛋白質。」

"With three important exceptions, there is little danger of protein deficiency in a plant food diet. The exceptions are diets very heavily dependent on [1] fruit or on [2] some tubers, such as sweet potatoes or cassava, or on [3] junk food (refined flours, sugars, and fat). Fortunately, relatively few people in the world try to survive on diets in which these foods are virtually the sole source of calories. In all other diets, if people are getting enough calories, they are virtually certain of getting enough protein."

美國飲食協會也糾正了早前關於蛋白質互補性的立場。這是其2009年對於素食主義的立場性文件的陳述：

The American Dietetic Association has also reversed its earlier position on protein complementarity. Here is a statement from its 2009 position paper on vegetarianism:

「如果滿足了攝取多種植物性食物並攝取足夠熱量的條件，純植物來源的蛋白質可以提供足夠量的必需氨基酸。」

"Plant sources of protein alone can provide adequate amounts of essential amino acids if a variety of plant foods are consumed and energy needs are met."

底線是什麼呢？

The bottom line?

植物蛋白與動物蛋白有不同的氨基酸比例。人類利用植物蛋白的效率較低，但卻為我們帶來益處。經由我們在特定的一餐或任何時間吃不同種類的植物性食物，植物蛋白不需要是「完全的」。不同種類的全蔬食可以提供所有必需氨基酸和所有蛋白質需求。

Plant proteins have different amino acid ratios from animal proteins. Humans use them less efficiently, which is actually beneficial for us. Plant proteins do not have to be "completed" by our combining different plant foods in a particular meal, or any time. A varied, whole food, plant-based diet provides all of the essential amino acids, and all the protein we need.

(4)關於蛋白質需求量的解釋

(4) A Note About Quantity

關於蛋白質的需求量也被誇大的問題。很多人相信我們通常需要比植物能夠提供的蛋白質還要多，而且那些過量的蛋白質完全不需要擔心。問題仍然是，我們真的能從植物獲得足夠蛋白質嗎？

The issue of protein quantity has been overblown as well. Many people believe we generally needmoreprotein than plants can provide, and that excess protein is nothing to be concerned about. The question remains though, can wereallyget enough protein from plants?

圖中：SD= standard deviations =σ=標準差 （譯註）

蛋白質推薦每日需求量（RDA）自從1943年設立以來每5年會重新複審一次（理論上來講，這個RDA量會達到或超過98%的人的生理需要），蛋白質需要量一直保持在大約佔8 – 10%的總熱量攝取。這個水平（RDA）實際上高於實驗方法確定的蛋白質需求量（估計平均需求量，或稱EAR）。全蔬食飲食方式也可提供8 – 10%蛋白質。

Set in 1943 and reviewed every five years since, the Recommended Daily Allowance (RDA) for protein (theoretically, the amount at which 98% of people will be meeting or exceeding their physiological needs) has remained at approximately 8-10% of total calories. This level is actually higher than the experimentally determined protein requirement (the Estimated Average Requirement, or EAR). A whole food, plant-based diet also provides 8-10% protein.

EAR：0.5 – 0.6克/公斤體重或（攝取足夠熱量）大約是4 – 5%的熱量來源於蛋白質。

EAR: 0.5 - 0.6 g of protein per kg of body weight or (for someone consuming sufficient calories) approximately4-5% total calories as protein.

RDA：EAR + 2標準差或（攝取足夠熱量）大約是8 – 10%熱量來源於蛋白質。（約0.8克/公斤體重）

RDA: EAR + 2 standard deviations or (for someone consuming sufficient calories) approximately8-10% total calories as protein.（approximately 0.8 g/kg body weight）

譯註：人奶的蛋白質含量約5%（熱量來源），人在嬰兒期是生長最快的時期，純母乳餵養即可滿足嬰兒的生長需要。而成人的平均蛋白質需求也大約是4 - 5%，即EAR可以滿足約50%的人的生理需要，而RDA則可滿足98%的人的生理需要。

例如：50公斤體重的人蛋白質需求量RDA = 50 * 0.8 = 40克/每天，EAR = 50 * （0.5 ~ 0.6）= 25 ~ 30克/每天

注釋：（8種必需氨基酸含量表）

Notes:

注1.坎貝爾（T.Colin Cambell）博士指出必須攝取8或9種必需氨基酸。人類需要8種必需氨基酸—圖中所示—是由William Rose 1952年確立的。組氨酸（Histidine），是最近增加的，也被認為是必需氨基酸，這是在發現對一項飲食中缺乏組氨酸對研究對象的血紅蛋白濃度的不利影響的研究後增加的。

1. Dr. Campbell notes that 8 or 9 amino acids are essential and must be consumed. Human requirements for 8 indispensable amino acids—the ones in the chart—were established by William Rose in 1952. Histidine, a more recent addition, is now considered indispensable as well, following a study showing that an absence of histidine in the diet had a detrimental effect on hemoglobin concentrations in research subjects.

注2.表中的值是基於每天吃2200卡路里的食物計算的，世界衛生組織（WHO）的「蛋白質安全攝取量」（0.83克/公斤每日蛋白攝取量），對一個60公斤（132磅）體重，每天適量活動之人的大約能量需要。

2. Values are calculated based on: a person eating a 2200 calorie diet, WHO』s "safe level of protein intake" ( 0.83 g/kg per day of protein) for a person of 60 kg (132#), and the approximate energy requirement for a moderately active person.

參考資料：

References:

Craig WJ, Mangels AR, American Dietetic Association. Position of the American Dietetic Association: vegetarian diets.J Am Diet Assoc2009 Jul; 109(7): 1266-82.

Food & Agriculture Organization. (2001). Human Energy Requirements Report of a Joint FAO/WHO/UNU Expert Consultation. Retrieved from:Italy.http://www.fao.org/docrep/007/y5686e/y5686e08.htm#bm08.

Lappe FM.Diet for a Small Planet.New York, NY, Ballantine Books. 1985.

McDougall J. The McDougall Plan. LaVerne TN, Ingram Book Company. 1983.

Osborn TB, Mendel LB. Amino Acids in Nutrition and Growth.J Biol Chem1914; 17: 325.

World Health Organization. (2007). Protein and Amino Acid Requirements in Human Nutrition: Report of a Joint WHO/FAO/UNU Expert Consultation. Retrieved from: http://whqlibdoc.who.int/trs/WHO_TRS_935_eng.pdf.

關於編譯者：老玉米是美國康奈爾大學坎貝爾營養研究中心《蔬食營養》證書持有者。老玉米的先生是美國內科醫生（MD），也是位「蔬食醫生」（Plantrician）。

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