你可能想不到最常见蔬食中就含有8种必需氨基酸
编译者前言：本来不想把文章弄的太长、太复杂，但后来想了下，还是尽量讲清楚比较好，因为人们长期以来被灌输了太多对植物蛋白质的观点，已经形成了“成见”，而打破“成见”是一个困难和复杂的过程。
您如果觉得太复杂，只需要看那张8种必需氨基酸含量表。
蛋白质的质量和数量
On Protein Quality and Quantity
（1）蛋白质的分类
（1）Protein Classifications
1914年，研究人员在研究试验室老鼠蛋白质需求时发现老鼠吃动物蛋白比吃植物蛋白要生长的更快速。其它研究也产生了同样的结果。
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.
当时，针对人类的蛋白质和氨基酸的需要尚不清楚，但科学家质疑植物性食物可能不支持老鼠的正常生长（或者也延伸到人类），因为植物性食物不包含足够量的特定种类氨基酸。
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.
动物性食物（肉、蛋、奶）因此被划分为“A类”蛋白质来源，而植物性食物（蔬菜和水果）则被看作劣等的，或者“B类”蛋白质来源。
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.
动物性食物 即 所谓的 “A 类” 蛋白质来源：
植物性食物 即 所谓的 “B类” 蛋白质来源：
（2）“高品质”的含义
（2）The Meaning of "High Quality"
所有动物必须持续补充身体中的蛋白质，从食物中摄取的蛋白质提供身体蛋白质合成所需的氨基酸。
All animals must continuously replenish their proteins, and the protein they take in through food provides the amino acids necessary for protein synthesis.
在所摄取的食物中每种氨基酸比例与摄食者体内每种氨基酸比例越接近，摄食者利用食物合成蛋白质的效率则越高。
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.
动物与其它动物之间的氨基酸比例比动物与植物之间的氨基酸比例更类似。因此，人类和其它动物利用所有动物性蛋白质的效率要超过所有植物性蛋白质。
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，动物性蛋白质被说成是有更高的生物价值，一直被描述成“高品质”蛋白质。
As a result, animal-based proteins are said to have higher biological value, and have been described as "high-quality" proteins.
从严格的科学观点来看，高价值、高品质蛋白质就单单是指能促进身体更有效率地合成蛋白质（因此细胞分裂和身体成长也更有效率）。
From a strictly scientific perspective, a high-value, high-quality protein is simply one that tends to promote more efficient protein synthesis (and therefore more efficient cell division and body growth.)
但是，这个术语暗指这类蛋白质是优越的 — 确实科学家使用这样的语言，因为他们假定这些蛋白质更优越。从消费者视角来看，当然更喜欢高价值、高品质的食物。但动物蛋白真的是更优越吗？
However, this terminology implies that such a protein is superior — and indeed scientists used this language because they assumed these proteins to be superior. From a consumer perspective，high-value, high-quality foods certainly sound preferable. But are they really?
（3）重新思考植物蛋白质的“问题”
（3）Rethinking the "Problem" with Plant Proteins
早期科学家并不知道蛋白质的高效利用率对人类来说并非是必然有利的。
Unbeknownst to early scientists, efficient protein utilization is not necessarily advantageous for humans.
因为事实证明，“高品质”蛋白质也倾向于促进非期望的（例如癌细胞和动脉粥样硬化组织）高效率生长。
As it turns out, "high-quality" proteins also tend to promote undesirable growth (such as that of cancer cells and atherogenic tissue) quite efficiently.
相比之下，植物蛋白的氨基酸组成 — 总是跟我们的有点不匹配 — 对促进非预期生长也是一样较低效率。然而，科学家还没有领会蛋白质与疾病之间的这种关系。
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“较低品质”的观点是因为它们提供的是“不完全”蛋白质（即蛋白质缺少某些特定的氨基酸），这造成很多人的忧虑，包括Frances Moore Lappe（拉佩），在她1971年出版的书《一座小行星的饮食方式》中将“蛋白质补充”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），一位推广素食以解决世界饥饿问题的社会学家，分享了早期科学家对植物蛋白质的顾虑。她得出结论（就像很多其他人一样）素食只有在吃了特定的包括所有必需氨基酸组合的情况下才是健康的。这种想法深深地植入了我们对蛋白质的共同想法 — 但事实并非如此。
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）植物与氨基酸
（4）Plants and Amino Acids
科学家现在明白了植物性食物确实含有所有必需氨基酸。
Scientists now understand that plant foods do contain all the essential amino acids.
请注意一些普通的植物性食物中氨基酸含量与世界卫生组织（WHO）所推荐量的比较：
Note how the amino acid contents of some common plant foods compare with World Health Organization (WHO) recommendations:
译注：图中只有糙米的赖氨酸（Lys）和总蛋白质含量比WHO推荐量稍低。
世界卫生组织（WHO）得出的结论是只要吃了足够热量，“很少会有天然食物不能提供足够必需氨基酸的情况，” 评论如下：
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:
“必需氨基酸确实存在于豆类、根茎类和谷类中，总的来说含量远超过推荐需求量，对于单一氨基酸有两个例外。第一，存在于木薯和红薯中的赖氨酸刚刚超过90%推荐需要量，而在谷类中的赖氨酸则介于57%至86%之间的推荐需要量…鉴于确认赖氨酸需求量的安全值存在不确定性，很明显这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."
即使谷物和木薯在有些实验室研究中理论上有轻微的“不足”，也许对人类健康会造成问题，如果我们吃不同种类的全蔬食并摄取足够的热量，限制“垃圾食品”和精制食物的话，这个问题是非常容易解决的。
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 a varied whole food, plant-based diet, limiting "junk" and refined foods.
换句话说，植物蛋白被称为“不完全”是因为跟我们人类氨基酸图谱不匹配，但在满足饮食需要方面它们并非“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.
同样地，术语“低质量”意为植物蛋白比动物蛋白使用起来有些低效率；然而，对人类健康来说低质量的说法则意味着误导。
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.
蛋白质“补充”是没有必要的。
Protein "complementing" is unnecessary.
Lappe（拉佩）是同意的。在《一座小行星的饮食方式》后来的版本中，她纠正了最初对蛋白质补充的看法，她写道：
Lappe agrees. In later editions of Diet for a Small Planet, she reversed her initial views on protein complementing, writing:
“在1971版本中我强调了蛋白质互补性，因为我假定唯一获得足够蛋白质的方法…是创造一种能像动物蛋白一样被人体利用的蛋白质。在对抗吃肉是唯一获得高质量蛋白质的神话时，我却制造了另一种神话。我给大众造成了一种印象，要想不吃肉而获得足够蛋白质就必须非常小心地选择食物。实际上，这远比我想象的容易。”
"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."
她补充道：
She adds:
“有三个重要例外，植物性饮食极少造成蛋白质缺乏。三种例外情况是饮食严重依赖 [1]水果 [2] 有些根茎类食物，比如红薯或木薯，或者[3] 垃圾食品（精制面粉，糖和油）。幸运的是，相对来讲世界上很少有人试图基本依赖这些食物作为单一热量来源为生。在其它各种饮食中，如果人们摄取了足够的热量，他们几乎肯定能获得足够的蛋白质。”
"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."
美国饮食协会也纠正了早前关于蛋白质互补性的立场。这是其2009年对于素食主义的立场性文件的陈述：
The American Dietetic Association has also reversed its earlier position on protein complementarity. Here is a statement from its 2009 position paper on vegetarianism:
“如果满足了摄取多种植物性食物并摄取足够热量的条件，纯植物来源的蛋白质可以提供足够量的必需氨基酸。”
"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."
底线是什么呢？
The bottom line?
植物蛋白与动物蛋白有不同的氨基酸比例。人类利用植物蛋白的效率较低，但却为我们带来益处。经由我们在特定的一餐或任何时间吃不同种类的植物性食物，植物蛋白不需要是“完全的”。不同种类的全蔬食可以提供所有必需氨基酸和所有蛋白质需求。
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) 关于蛋白质需求量的解释
(4) A Note About Quantity
关于蛋白质的需求量也被夸大的问题。很多人相信我们通常需要比植物能够提供的蛋白质还要多，而且那些过量的蛋白质完全不需要担心。问题仍然是，我们真的能从植物获得足够蛋白质吗？
The issue of protein quantity has been overblown as well. Many people believe we generally need more protein than plants can provide, and that excess protein is nothing to be concerned about. The question remains though, can we really get enough protein from plants?
图中：SD = standard deviations = σ = 标准差 （译注）
蛋白质推荐每日需求量（RDA）自从1943年设立以来每5年会重新复审一次（理论上来讲，这个RDA量会达到或超过98%的人的生理需要），蛋白质需要量一直保持在大约占8 – 10%的总热量摄取。 这个水平（RDA）实际上高于实验方法确定的蛋白质需求量（估计平均需求量，或称EAR）。全蔬食饮食方式也可提供8 – 10% 蛋白质。
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 体重或（摄取足够热量）大约是 4 – 5% 的热量来源于蛋白质。
EAR: 0.5 - 0.6 g of protein per kg of body weight or (for someone consuming sufficient calories) approximately 4-5% total calories as protein.
RDA：EAR + 2 标准差或（摄取足够热量）大约是 8 – 10% 热量来源于蛋白质。（约 0.8 克/公斤体重）
RDA: EAR + 2 standard deviations or (for someone consuming sufficient calories) approximately 8-10% total calories as protein. （approximately 0.8 g/kg body weight）
译注：人奶的蛋白质含量约 5%（热量来源），人在婴儿期是生长最快的时期，纯母乳喂养即可满足婴儿的生长需要。而成人的平均蛋白质需求也大约是 4 - 5%，即EAR可以满足约50% 的人的生理需要，而RDA则可满足98%的人的生理需要。
例如：50公斤体重的人蛋白质需求量 RDA = 50 * 0.8 = 40 克/每天，EAR = 50 * （0.5 ~ 0.6）= 25 ~ 30 克/每天
注释：（8种必需氨基酸含量表）
Notes:
注1.坎贝尔（T.Colin Cambell）博士指出必须摄取8或9种必需氨基酸。人类需要8种必需氨基酸—图中所示—是由William Rose 1952年确立的。组氨酸（Histidine），是最近增加的，也被认为是必需氨基酸，这是在发现对一项饮食中缺乏组氨酸对研究对象的血红蛋白浓度的不利影响的研究后增加的。
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. 表中的值是基于每天吃2200卡路里的食物计算的，世界卫生组织（WHO）的“蛋白质安全摄取量”（0.83 克/公斤每日蛋白摄取量），对一个60公斤（132磅）体重，每天适量活动之人的大约能量需要。
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.
参考资料：
References:
Craig WJ, Mangels AR, American Dietetic Association. Position of the American Dietetic Association: vegetarian diets. J Am Diet Assoc 2009 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 Chem 1914; 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.
关于编译者：老玉米是美国康奈尔大学坎贝尔营养研究中心《蔬食营养》证书持有者。老玉米的先生是美国内科医生（MD），也是位“蔬食医生”（Plantrician）。
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