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What Foods Are in the Protein Foods Group?

All foods made from meat, poultry, seafood, beans and peas, eggs, processed soy products, nuts, and seeds are considered part of the Protein Foods Group. Beans and peas are also part of the Vegetable Group. For more information on beans and peas, see Beans and Peas Are Unique Foods.
Select a variety of protein foods to improve nutrient intake and health benefits, including at least 8 ounces of cooked seafood per week. Young children need less, depending on their age and calorie needs. The advice to consume seafood does not apply to vegetarians. Vegetarian options in the Protein Foods Group include beans and peas, processed soy products, and nuts and seeds. Meat and poultry choices should be lean or low-fat.

View Protein Foods Gallery

Commonly eaten protein foods

• Meats*

  
  

  Lean cuts of:

  • beef
  • ham
  • lamb
  • pork
  • veal
  
  

  Game Meats

  • bison
  • rabbit
  • venison
  
  

  Lean Ground Meats

  • beef
  • pork
  • lamb
  
  

  Lean luncheon or deli meats

  
  

  Organ Meats

  • liver
  • giblets

  Poultry*

  • chicken
  • duck
  • goose
  • turkey
  • ground chicken and turkey

  Eggs*

  • chicken eggs
  • duck eggs

  Beans and Peas

  • bean burgers
  • black beans
  • black-eyed peas
  • chickpeas (garbanzo beans)
  • falafel
  • kidney beans
  • lentils
  • lima beans (mature)
  • navy beans
  • pinto beans
  • soy beans
  • split peas
  • white beans

  Processed Soy Products

  • tofu (bean curd made from soybeans)
  • veggie burgers
  • tempeh
  • texturized vegetable protein (TVP)

• Nuts and Seeds*

  • almonds
  • cashews
  • hazelnuts (filberts)
  • mixed nuts
  • peanuts
  • peanut butter
  • pecans
  • pistachios
  • pumpkin seeds
  • sesame seeds
  • sunflower seeds
  • walnuts

  Seafood*

  
  

  Finfish such as:

  • catfish
  • cod
  • flounder
  • haddock
  • halibut
  • herring
  • mackerel
  • pollock
  • porgy
  • salmon
  • sea bass
  • snapper
  • swordfish
  • trout
  • tuna
  
  

  Shellfish such as:

  • clams
  • crab
  • crayfish
  • lobster
  • mussels
  • octopus
  • oysters
  • scallops
  • squid (calamari)
  • shrimp
  
  

  Canned fish such as:

  • anchovies
  • clams
  • tuna
  • sardines

*Selection Tips

• Choose lean or low-fat meat and poultry. If higher fat choices are made, such as regular ground beef (75 to 80% lean) or chicken with skin, the fat counts against your maximum limit for empty calories (calories from solid fats or added sugars).
• If solid fat is added in cooking, such as frying chicken in shortening or frying eggs in butter or stick margarine, this also counts against your maximum limit for empty calories (calories from solid fats and added sugars).
• Select some seafood that is rich in omega-3 fatty acids, such as salmon, trout, sardines, anchovies, herring, Pacific oysters, and Atlantic and Pacific mackerel.
• Processed meats such as ham, sausage, frankfurters, and luncheon or deli meats have added sodium. Check the Nutrition Facts label to help limit sodium intake. Fresh chicken, turkey, and pork that have been enhanced with a salt-containing solution also have added sodium. Check the product label for statements such as “self-basting” or “contains up to __% of __”, which mean that a sodium-containing solution has been added to the product.
• Choose unsalted nuts and seeds to keep sodium intake low.

植物蛋白和动物蛋白

蛋白质如此重要，因此在19世纪早期有几位著名的营养学家曾经鼓吹“蛋白质至上论”，他们 认为：如果你是个有教养的人，你应该摄入大量蛋白；如果你是有钱的人，你应该多摄入肉食；如果你是穷人，你只要靠素食，比如马铃薯来果腹。社会阶层越低的 人，通常被看做懒散、没有能力的人，是肉类和蛋白质摄入不足的结果。这种社会精英主义的傲慢和偏见，是19世纪营养学领域内占统治地位的观点。当时的概念 是“强壮就是好的”，是更有教养、更高尚的象征。这种观点在某种程度上更使得蛋白质的偏见充斥到社会中。

植物蛋白和动物蛋白

很多人认为人类膳食中蛋白质的来源以动物性食物较植物性为优越。如果按照这种说法，那么“人肉”中的蛋白质才是最最优越的，它和我们身体所需要的蛋 白质恰好一模一样，可惜人类没有吃同类的习惯。其他动物的蛋白和人体蛋白其实也非常接近，这些蛋白质能够提供我们所需的多数氨基酸，而且这些氨基酸也能被 我们的身体所吸收和利用，因此这些蛋白质往往被称为“高品质蛋白”。但是对于蛋白质来说，最终的目的是被人体利用，因此蛋白质含量虽多，但利用效率不高也 是不行的，“效率”才是揭示一种蛋白好坏的关键。有大量的研究表明，所谓低品质的植物蛋白，尽管用于合成新蛋白质的速度比较慢，但是很稳定，这种蛋白才是 最健康的蛋白，也是身体最需要的蛋白。

有必要说一下的“植物蛋白”

人从动物或蔬菜中得到必需的蛋白质，乳类食物、蛋类、动物的肉都含有动物蛋白质，所有的蔬菜亦含有蛋白质，豌豆和豆荚中含有的蛋白质尤其多。许多人 认为我们不能从纯植物中获得力量与健康。但事实是吃草的动物只用草与叶来建造强壮的肌肉和骨骼。大象只吃树叶，而树叶中的钙蛋白却营养着大象庞大的象牙； 漂亮的麋鹿每年都会更换它们硕大的鹿角，而它们的饮食却只有水生植物和草料。通过消化与同化，人体将食物的蛋白质分解成它们的基质——氨基酸。我们必须记 住这一点：不管氨基酸的来源是植物还是动物的，它们都是同样的氨基酸。作为食物，它们对身体同样有用。

Amino Acid Scoring

Amino acid scoring provides a way to predict how efficiently protein will meet a person’s amino acid needs. This concept assumes that tissue protein synthesis is limited unless all required amino acids are available at the same time and in appropriate amounts at the site of tissue protein synthesis.

A reference amino acid scoring pattern is used, which expresses the amino acids requirements in milligrams/gram of dietary protein or as percentages in an “ideal” protein. For example, if the lysine content of a whole-wheat flour is 2.6% and the value for lysine in the scoring pattern for a young child is 5.1%, you would calculate 2.6/5.1´100=51. If 51 is the lowest score among all of the amino acids in whole-wheat flour, it is named the “limiting amino acid,” and the amino acid score for wheat proteins would equal 51. The score for whole egg proteins is 100, so a child would have to consume twice as much protein from whole wheat as from eggs.

A group of consultants from the Food and Agriculture Organization of the United Nations (FAO)/World Health Organization (WHO) suggested discontinuation of the use of the amino acid scoring patterns for school-age children and adults. It recommended the use of the amino acid scoring pattern for children of preschool age to evaluate protein quality for all age groups except infants. The pattern used for infants is based on the amino acid composition of human milk.

Protein intake

For the population of industrialized nations, the intake of protein far surpasses the recommended amount. Older children and adults have little chance of not meeting their amino acid and protein nitrogen needs. The only people who really need to worry about the quality of their protein are those who eat very little protein and that is rare.

Protein digestibility-corrected amino acid score (PDCAAS)

Amino acid scoring does not take protein digestibility into account. Therefore, it is useful for comparing animal products and refined foods that are not excessively heated. However, because plant foods are not completely digested, it is necessary to make a correction to the calculation.

The PDCAAS was adopted by FAO/WHO as the preferred method for measuring protein value in human nutrition. It is calculated by comparing the concentration of the first limiting essential amino acid in the test protein with the concentration of that amino acid in the scoring pattern, and then correcting for true fecal digestibility of the test protein.

The three concerns about the PDCAAS are:

·   The validity of the preschool-age child amino acid requirements

·   The validity of correcting the score based on fecal digestibility, instead of ileal digestibility

o “Fecal digestibility overestimates the nutritional value of a protein, because amino acid nitrogen entering the colon is lost for protein synthesis in the body and is, at least in part, excreted in urine as ammonia” (Schaafsma G)

·   PDCAAS values larger than 100 are currently truncated to 100

Suggested Amino Acid Scoring Patterns (mg/g Protein)
	Infant	Preschool Child
Histidine	26	(19)
Isoleucine	46	28
Leucine	93	66
Lysine	66	58
Methionine + Cystine	42	25
Phenylalanine + Tyrosine	72	63
Threonine	43	34
Tryptophan	17	11
Valine	55	35
TOTAL	460	339

Histidine value in parenthesis obtained from interpolation from smooth curve of requirement (Harper AE, Yoshimura NN).

g=gram, mg=milligram

The perfect score?

If you ate a food with an amino acid score of 75 and ate another food with an amino acid score of 25, would your meal have a perfect amino acid score? Unfortunately, it is not that easy. The amino acids would have to compliment each other perfectly, and the chances of this occurring are slim.

References and recommended readings

Harper AE, Yoshimura NN. Amino acid balance and use in the body. Available at: http://www.oralchelation.com/technical/amino1.htm#11. Accessed July 28, 2010.

Schaafsma G. The protein digestibility amino acid score. J Nutr [serial online]. 2000;130:1865S-1867S. Available at: http://jn.nutrition.org/cgi/content/full/130/7/1865S. Accessed July 28, 2010.

Review Date 9/10

G-1386

酶这种蛋白质

酶是我们身体的劳动力。它们支持着我们的生命，能在人体温和的条件下，高效率地催化各种生 物化学反应，促进新陈代谢。生命活动中的消化、吸收、呼吸、运动和生殖都是酶促反应的过程。这是一个非常重要的过程。每种酶都有自己特定的工作要做。酶只 能在一定限度的温度中工作。酶催化的化学反应一般是在较温和的条件下进行的，过热或过冷都会破坏酶。摄氏46度以上的温度就会将酶杀死，让它们变得毫无用 处。为什么我们强调不管什么时候只要将蔬菜微微煮一下就好？就是这个原因。酶在未经加工的新鲜食物中的数量更加充裕。酶很脆弱，轻易地就会成为外来入侵者 的牺牲品。正如许多物质会损害我们的免疫系统一样，酶也有许多让它讨厌的东西，多得可以列出一份清单：酒精、烟草、毒品、咖啡、饮用水中的氟化物和氯、添 加剂和防腐剂。此外，对食物的提炼、加工处理、加热杀菌都会破坏酶。所有这些原因，都要求我们吃那些最天然的食物。压力也会大大减少我们身体中酶的供应 量。

Protein Digestibility Corrected Amino Acid Score

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Protein Digestibility Corrected Amino Acid Score (PDCAAS) is a method of evaluating the protein quality based on both the amino acid requirements of humans and their ability to digest it. The PDCAAS rating was adopted by the US Food and Drug Administration (FDA) and the Food and Agricultural Organization of the United Nations/World Health Organization (FAO/WHO) in 1993 as "the preferred 'best'" method to determine protein quality. These organizations have suggested that other methods for evaluating the quality of protein are inferior.^[1]

Contents 1 PDCAAS value of protein 2 Methodology 3 Limitations 4 See also 5 References

PDCAAS value of protein

A PDCAAS value of 1 is the highest, and 0 the lowest. The table shows the ratings of selected foods. ^{[2][3][4] [5]}

1.00	casein (milk protein)
1.00	egg white
1.00	soy protein
1.00	whey (milk protein)
0.99	mycoprotein
0.92	beef
0.91	soybeans
0.78	chickpeas
0.76	fruits
0.75	black beans
0.73	vegetables
0.70	Other legumes
0.59	cereals and derivatives
0.52	peanuts
0.42	whole wheat

Methodology

The formula for calculating the PDCAAS percentage is: (mg of limiting amino acid in 1 g of test protein / mg of same amino acid in 1 g of reference protein) x fecal true digestibility percentage.^[2]
The PDCAAS value is different from measuring the quality of protein from the protein efficiency ratio (PER) and the biological value (BV) methods.^[5] The PER was based upon the amino acid requirements of growing rats, which noticeably differs from that of humans. The PDCAAS allows evaluation of food protein quality based on the needs of humans as it measures the quality of a protein based on the amino acid requirements (adjusted for digestibility) of a 2- to 5-year-old child (considered the most nutritionally-demanding age group). The BV method uses nitrogen absorption as a basis. However, it does not take into account certain factors influencing the digestion of the protein and is of limited use for application to human protein requirements because what is measured is maximal potential of quality and not a true estimate of quality at requirement level. Nevertheless, BV can be used to assess requirements of protein derived from foods with known quality differences and measure the proportion of absorbed nitrogen which is retained and presumably used for protein synthesis as an accurate indicator for protein measurement.^[6]
Using the PDCAAS method, the protein quality rankings are determined by comparing the amino acid profile of the specific food protein against a standard amino acid profile with the highest possible score being a 1.0. This score means, after digestion of the protein, it provides per unit of protein 100 percent or more of the indispensable amino acids required.
The FDA gave two reasons for adopting the PDCAAS in 1993: 1) PDCAAS is based on human amino acid requirements, which makes it more appropriate for humans than a method based on the amino acid needs of animals. 2) The Food and Agricultural Organization/World Health Organization (FAO/WHO) had previously recommended PDCAAS for regulatory purposes.

Limitations

Amino acids that move beyond the terminal ileum in the body are less likely to be absorbed for use in protein synthesis. They may pass out of the body, or may be absorbed by bacteria, and thus will not be present in the faeces, and will appear to have been digested. The PDCAAS takes no account of where the proteins have been digested.
Similarly, amino acids that are lost due to antinutritional factors present in many foods are assumed to be digested according to the PDCAAS.
The PDCAAS method may also still be considered incomplete, since human diets, except in times of famine, almost never contain only one kind of protein. However, calculating the PDCAAS of a diet solely based on the PDCAAS of the individual constituents is impossible. This is because one food may provide an abundance of an amino acid that the other is missing, in which case the PDCAAS of the diet is higher than that of any one of the constituents. To arrive at the final result, all individual amino acids would have to be taken into account, though, so the PDCAAS of each constituent is largely useless.
For example, grain protein has a PDCAAS of about 0.4 to 0.5, limited by lysine. On the other hand, it contains more than enough methionine. White bean protein (and that of many other pulses) has a PDCAAS of 0.6 to 0.7, limited by methionine, and contains more than enough lysine. When both are eaten in roughly equal quantities in a diet, the PDCAAS of the "combined constituent" is 1.0, because each constituent's protein is complemented by the other.
A more extreme example would be the combination of gelatine (which contains virtually no tryptophan and thus has a PDCAAS of 0) with isolated tryptophan (which, lacking all other essential amino acids, also has a PDCAAS of 0). Despite individual scores of 0, the combination of both in adequate amounts has a positive PDCAAS, with the limiting amino acids isoleucine, threonine and methionine. Further, according to a recent 2000 study by scientist Gerjan Schaafsma, "The questions about the validity of the amino acid scoring pattern and the application of the true fecal rather than the true ideal digestibility correction as well as the truncation of PDCAAS values warrant a critical evaluation of PDCAAS in its current form as a measure of protein quality in human diets."^[2] Also, the scientific community has raised critical questions about the validity of PDCAAS.^{[specify][7][8]}
In addition the fact that four proteins, all with different amino acid profiles, receive identical scores of 1.0 limits its usefulness as a comparative tool. Since they have different compositions, it is natural to assume that they perform differently in the human body and should have different scores. In short, this method, however, gives no distinction of their performance relative to each other because after they pass a certain point, they are all capped at 1.0 and receive an identical rating.^[5][9][10]
This is because in 1990 at a FAO/WHO meeting, it was decided that proteins having values higher than 1.0 would be rounded or "leveled down" to 1.0 as scores above 1.0 are considered to indicate the protein contains essential amino acids in excess of the human requirements.^[11]

Soy protein

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Soy protein is a protein that is isolated from soybean. It is made from soybean meal that has been dehulled and defatted. Dehulled and defatted soybeans are processed into three kinds of high protein commercial products : soy flour, concentrates, and isolates. Soy protein isolate has been used since 1959 in foods for its functional properties. Recently, soy protein popularity has increased due to its use in health food products, and many countries allow health claims for foods rich in soy protein.
Soy protein is generally regarded as the storage protein held in discrete particles called protein bodies, which are estimated to contain at least 60–70% of the total soybean protein.^[1] Upon germination of the soybean, the protein will be digested, and the released amino acids will be transported to locations of seedling growth. Soybeans contain a small but newly very significant 2S Albumin storage protein.^[2][3] Legume proteins, such as soy and pulses, belong to the globulin family of seed storage proteins called legumin and vicilins, or in the case of soybeans, glycinin and beta-conglycinin. All grains, except for oats, contain a third type of storage protein called gluten or prolamin. Soybeans also contain biologically active or metabolic proteins, such as enzymes, trypsin inhibitors, hemagglutinins, and cysteine proteases very similar to papain. The soy cotyledon storage proteins, important for human nutrition, can be extracted most efficiently by water, water plus dilute alkali (pH 7–9), or aqueous solutions of sodium chloride (0.5–2 M) from dehulled and defatted soybeans that have undergone only a minimal heat treatment so the protein is close to being native or undenatured. Soy protein contains phytoestrogens, which bind to estrogen receptors in the body.

Contents 1 History 2 Food uses 3 Functional uses 4 Production methods 5 Product types 5.1 Isolates 5.2 Concentrates 5.3 Flours 6 Nutrition 6.1 Biological value 7 Role in the growth of the soybean plant 8 Health 9 Uses 9.1 Textured soy protein 10 See also 11 References 12 External links

History

Soy protein has been available since 1936 for its functional properties. In that year, organic chemist Percy Lavon Julian designed the world's first plant for the isolation of industrial-grade soy protein called alpha protein.^[4] The largest use of industrial-grade protein was, and still is, for paper coatings, in which it serves as a pigment binder. However, Julian's plant must have also been the source of the "soy protein isolate" which Ford's Robert Boyer and Frank Calvert spun into an artificial silk that was then tailored into that now famous "silk is soy" suit that Henry Ford wore on special occasions. The plant's eventual daily output of 40 tons of soy protein isolate made the Soya Products Division into Glidden's most profitable division.
At the start of the Second World War, Glidden sent a sample of Julian's isolated soy (alpha) protein to National Foam System Inc. (today a unit of Kidde Fire Fighting) which used it to develop Aero-Foam,^[5][6] used by the U.S. Navy for fire fighting and referred to as "bean soup". While not exactly the brainchild of Dr. Julian, it was the meticulous care given to the preparation of the soy protein that made the fire fighting foam possible. When a hydrolysate of isolated soy protein was fed into a water stream, the mixture was converted into a foam by means of an aerating nozzle. The soy protein foam was used to smother oil and gasoline fires aboard ships, and was particularly useful on aircraft carriers. It saved the lives of thousands of sailors.^[7]
In 1958, Central Soya of Fort Wayne, Indiana, acquired Julian's Soy Products Division (Chemurgy) of the Glidden Paint Company, Chicago. Central Soya's Bunge Protein Division, in January, 2003, joined/merged with DuPont's soy protein business Solae, which in 1997 had acquired Ralston Purina's soy division, Protein Technologies International (PTI) in St. Louis. On May 1, 2012 DuPont announced its complete acquisition of Solae from Bunge,^[8][9]
Food-grade soy protein isolate first became available on October 2, 1959 with the dedication of Central Soya's edible soy isolate, Promine D, production facility on the Glidden Company industrial site in Chicago. An edible soy isolate and edible spun soy fiber have also been available since 1960 from the Ralston Purina Company in St. Louis, who had hired Boyer and Calvert. In 1987, PTI became the world's leading maker of isolated soy protein.

Food uses

Soy protein is used in a variety of foods, such as salad dressings, soups, meat analogues, beverage powders, cheeses, nondairy creamer, frozen desserts, whipped topping, infant formulas, breads, breakfast cereals, pastas, and pet foods.

Functional uses

Soy protein is used for emulsification and texturizing. Specific applications include adhesives, asphalts, resins, cleaning materials, cosmetics, inks, pleather, paints, paper coatings, pesticides/fungicides, plastics, polyesters, and textile fibres.

Production methods

Edible soy protein "isolate" is derived from defatted soy flour with a high solubility in water (high NSI). The aqueous extraction is carried out at a pH below 9. The extract is clarified to remove the insoluble material and the "supernatant" is acidified to a pH range of 4-5. The precipitated protein-curd is collected and separated from the whey by centrifuge. The curd is usually neutralized with alkali to form the sodium proteinate salt before drying
Soy protein concentrate is produced by immobilizing the soy globulin proteins while allowing the soluble carbohydrates, soy whey proteins, and salts to be leached from the defatted flakes or flour. The protein is retained by one or more of several treatments: leaching with 20-80% aqueous alcohol/solvent, leaching with aqueous acids in the isoelectric zone of minimum protein solubility, pH 4-5; leaching with chilled water (which may involve calcium or magnesium cations), and leaching with hot water of heat-treated defatted soy meal/flour.
All of these processes result in a product that is 70% protein, 20% carbohydrates (2.7 to 5% crude fiber), 6% ash and about 1% oil, but the solubility may differ. One tonne of defatted soybean flakes will yield about 750 kg of soybean protein concentrate.

Product types

Isolates

Soy protein isolate is a highly refined or purified form of soy protein with a minimum protein content of 90% on a moisture-free basis. It is made from defatted soy flour which has had most of the nonprotein components, fats and carbohydrates removed. Because of this, it has a neutral flavor and will cause less flatulence due to bacterial fermentation.
Soy isolates are mainly used to improve the texture of meat products, but are also used to increase protein content, to enhance moisture retention, and are used as an emulsifier. Flavor is affected,^{[citation needed]} but whether it is an enhancement is subjective.^[opinion]
Before 2006, the U.S. Food and Drug Administration (FDA) was examining flavor reversion concerns related to levels of the toxin furan in soy protein isolate and other foods.^[10] This problem has been solved by David Min of the Ohio Agricultural Research and Development Center. The chlorophyll in soy oil was reacting in the presence of light to form trans-2-heptenal and 2- pentenylfuran. Chlorophyll in soy oil is now removed with diatomaceous earth filters.
Pure soy protein isolate is used mainly by the food industry. It is sometimes available in health stores or in the pharmacy section of the supermarket. It is usually found combined with other food ingredients.

Concentrates

Soy protein concentrate is about 70% soy protein and is basically defatted soy flour without the water-soluble carbohydrates. It is made by removing part of the carbohydrates (soluble sugars) from dehulled and defatted soybeans.
Soy protein concentrate retains most of the fiber of the original soybean. It is widely used as functional or nutritional ingredient in a wide variety of food products, mainly in baked foods, breakfast cereals, and in some meat products. Soy protein concentrate is used in meat and poultry products to increase water and fat retention and to improve nutritional values (more protein, less fat).
Soy protein concentrates are available in different forms: granules, flour and spray-dried. Because they are very digestible, they are well-suited for children, pregnant and lactating women, and the elderly. They are also used in pet foods, milk replacements for babies (human and livestock), and even used for some nonfood applications.

Flours

Soy flour is made by grinding soybeans into a fine powder. It comes in three forms: natural or full-fat (contains natural oils); defatted (oils removed) with 50% protein content and with either high water solubility or low water solubility; and lecithinated (lecithin added). As soy flour is gluten-free, yeast-raised breads made with soy flour are dense in texture.
Soy grits are similar to soy flour except the soybeans have been toasted and cracked into coarse pieces. Kinako is a soy flour used in Japanese cuisine.

Nutrition

Soybean protein is a "complete protein" since it provides all of the essential amino acids for human nutrition.^[11][12] Soybean protein is essentially identical to that of other legume pulses (that is to say, legume proteins in general consist of 7S and 11S storage proteins), and is one of the least expensive sources of dietary protein.^[13] For this reason, soy is important to many vegetarians and vegans.
Of any studied legume, whole soybeans have the highest levels of phytic acid, an organic acid and mineral chelator present in many plant tissues, especially bran and seeds, which binds to certain ingested minerals: calcium, magnesium, iron, and especially zinc — in the intestinal tract, and reduces the amount the body assimilates. For people with a particularly low intake of essential minerals, especially young children and those in developing countries, this effect can be undesirable. However, dietary mineral chelators help prevent overmineralization of joints, blood vessels, and other parts of the body, which is most common in older persons.
The digestibility of some soyfoods are as follows: steamed soybeans 65.3%, tofu 92.7%, soy milk 92.6%, and soy protein isolate 93–97%.^[14][15] Some studies on rats have indicated the biological value of soy protein isolates is comparable to animal proteins such as casein if enriched with the sulfur-containing amino acid methionine.^[16]
Lafayette Mendel and Morris S. Fine of the Sheffield Laboratory of Physiological Chemistry at Yale University made the observation in the September 1911 edition of the Journal of Biological Chemistry that soybeans produce a positive nitrogen (N) balance in a human subject when they conducted a study to determine the utilization of legume proteins. The treatment called for five days of a 2,400 calories (10,000 kJ) diet consisting of meat, eggs, nut butter, potatoes, and fruit, followed by six days where 90.5% of total nitrogen was supplied by soybeans, and then another five days of the first diet, minus the nut butter. They discovered the soybean nitrogen is "distinctly (if only slightly) less well utilized than that of the preceding and succeeding mixed diets".^[17]
When measuring the nutritional value of protein, the original protein efficiency ratio (PER) method, first proposed by Thomas Burr Osborne and Lafayette Mendel in 1917, was the most widely used method until 1990. This method was found to be flawed for the biological evaluation of protein quality because the young rats used in the study had higher relative requirements for sulfur-containing amino acids than did humans. As such, the analytical method universally recognized by the FAO/WHO (1990), as well as the FDA, USDA, United Nations University and the National Academy of Sciences when judging the quality of protein is the protein digestibility-corrected amino acid score, as it is viewed as accurately measuring the correct relative nutritional value of animal and vegetable sources of protein in the diet.^[18][19] Based on this method, soy protein is considered to have a similar equivalent in protein quality to animal proteins. Egg white has a score of 1.00, soy concentrate 0.99, beef 0.92, and isolated soy protein 0.92. In 1990 at an FAO/WHO meeting, it was decided that proteins having values higher than 1.0 would be rounded or "leveled down" to 1.0, as scores above 1.0 are considered to indicate the protein contains essential amino acids in excess of the human requirements.^[20]

Biological value

Main article: Biological Value

Another measure of a protein's use in nutrition is the biological value scale, which dates back to 1911; it relies on nitrogen retention as a measurement of protein quality. Soybean protein isolate has a biological value of 74.^[21] Whole soybean has a biological value of 96, and soy milk 91.^[22]

Role in the growth of the soybean plant

Soy protein is generally regarded as stored protein held in discrete particles called "protein bodies" estimated to contain at least 60% to 70% of the total protein within the soybean. This protein is important to the growth of new soybean plants, and when the soybean germinates, the protein will be digested, and the released amino acids will be transported to locations of seedling growth. Legume proteins, such as soy and pulses, belong to the globulin family of seed storage proteins called legumin (11S globulin fraction) and vicilins (7S globulin), or in the case of soybeans, glycinin and beta-conglycinin.^[23][24] Grains contain a third type of storage protein called gluten or "prolamines". Edestin, a legumin class reserve protein from hemp seeds have six identical subunits. There is one hexameric protein in the rhombohedral unit cell.^[25]
Soybeans also contain biologically active or metabolic proteins, such as enzymes, trypsin inhibitors, hemagglutinins, and cysteine proteases very similar to papain. The soy cotyledon storage proteins, important for human nutrition, can be extracted most efficiently by water, water plus dilute alkali (pH 7–9), or aqueous solutions of sodium chloride (0.5–2 M) from dehulled and defatted soybeans that have undergone only a minimal heat treatment so the protein is close to being native or undenatured.^[26] Soybeans are processed into three kinds of modern protein-rich products: soy flour, soy concentrate, and soy isolate.
For the 11S protein, glycinin, to fold properly into its hexagonal shape(containing six subunits, a hexamer), it must undergo a very limited proteolysis^[27][28][29] in a manner similar to the cleavage of a peptide from proinsulin to obtain active insulin.

Health

See also: Soy controversy

A meta-analysis concluded soy protein is correlated with significant decreases in serum cholesterol, low density lipoprotein (LDL, bad) cholesterol and triglyceride concentrations.^[30] However, high density lipoprotein (HDL, good) cholesterol did not increase. Soy phytoestrogens (isoflavones: genistein and daidzein) adsorbed onto the soy protein were suggested as the agent reducing serum cholesterol levels. On the basis of this research, PTI, in 1998, filed a petition with FDA for a health claim that soy protein may reduce cholesterol and the risk of heart disease.
The FDA granted this health claim for soy: "25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease." One serving, (1 cup or 240 mL) of soy milk, for instance, contains 6 or 7 grams of soy protein.
In January 2006, an American Heart Association review of a decade-long study of soy protein benefits cast doubt on the FDA allowed "Heart Healthy" claim for soy protein. The panel also found soy isoflavones do not reduce postmenopause "hot flashes" in women, nor do isoflavones help prevent cancers of the breast, uterus, or prostate. Thus, soy isoflavones in the form of supplements are not recommended. Among the conclusions, the authors state, "In contrast, soy products such as tofu, soy butter, soy nuts, or some soy burgers should be beneficial to cardiovascular and overall health because of their high content of polyunsaturated fats, fiber, vitamins, and minerals and low content of saturated fat. Using these and other soy foods to replace foods high in animal protein that contain saturated fat and cholesterol may confer benefits to cardiovascular health." ^[31]
In February 2012, the European Food Safety Agency (EFSA) published a scientific opinion on isolated soy proteins and reduction of blood LDL-cholesterol concentrations. The EFSA took into account that only four vs fourteen randomized controlled trials (RCTs) reported an effect of ISP on blood LDL/non-HDL cholesterol concentrations, while the rest shows no effects. The EFSA concludes that a cause and effect relationship has not been established between the consumption of ISP and a reduction in blood LDL-cholesterol concentrations.
Soy is also rich in estrogenic compounds, such as genistein and daidzein; however, research is conflicting as to whether or not it can cause increases in estrogen in males.^[32]
A 2007 study by Goodin et al. reported that 56g of soy protein powder per day caused serum testosterone to fall 4% in four weeks in a test group of 12 healthy males. (An error in the abstract said 19%, and this figure was erroneously reported by the media.) ^[33]) According to the study, the data supported further studies of these hormonal effects as a mechanism in prostate cancer prevention.^[34] However, a study conducted by the Miami Research Associates refutes the finding of the Goodin study, finding soy protein had no significant impact on testosterone levels in healthy males.^[35] In fact, only one participant in the Goodin study actually saw a drop in testosterone. The participant in question had testosterone levels 200% higher than all of the other subjects, and during the study, his levels dropped to bring him in line with the other participants. The Goodin study did not conclusively suggest the participant's erratic testosterone levels were related to the soy protein.
Lunasin, a 43 amino acid soy peptide, has been reported to reduce inflammation by reducing interleukin 6, and may help in leukemia.^{[3][36][37][38]}

Uses

Textured soy protein

For more details on this topic, see Textured soy protein.

Textured soy protein (TSP) is made by forming a dough from high nitrogen solubility index (NSI) defatted soy flour with water in a screw-type extruder, and heating with or without steam. The dough is extruded through a die into various possible shapes: granules, flakes, chunks, goulash, steakettes (schnitzel), etc., and dried in an oven. TSP made from soy flour contains 50% soy protein and must be rehydrated before use at a weight ratio of 1 TSP:2 water. However, TSP, when made from soy concentrate, contains 70% protein and can be rehydrated at a ratio of 1:3. It can be used as a meat replacement or supplement. The extrusion technology changes the structure of the soy protein, resulting in a fibrous, spongy matrix similar in texture to meat.
While TSP has a shelf life of more than a year when stored dry at room temperature, it should be used at once or stored for no more than three days in the refrigerator after rehydration. It is usually rehydrated with cold or hot water, but a bit of vinegar or lemon juice can be added to quicken the process. In the rehydration step of TSP, excess hot water is useful to leach out flatulence-producing carbohydrates.^{[original research?]}
Soy protein products such as TSP are used as low-cost substitutes in meat and poultry products.^[39][40] Food service, retail and institutional (primarily school lunch and correctional) facilities regularly use such "extended" products. Extension may result in diminished flavor, but fat and cholesterol are reduced. Vitamin and mineral fortification can be used to make soy products nutritionally equivalent to animal protein; the protein quality is already roughly equivalent. The soy-based meat substitute textured vegetable protein has been used for more than 50 years as a way of inexpensively and safely extending ground beef up to 30% for hamburgers, without reducing its nutritional value.^[41][42][43]
Rehydrated TSP flakes can also replace, at a minimum, 33% of the tuna fish in tuna salad. It is high in protein and low in fat and sodium.

Edible protein per unit area of land

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This article's factual accuracy may be compromised due to out-of-date information. Please help improve the article by updating it. There may be additional information on the talk page. (June 2012)

Edible protein per unit area of land is a measure of agricultural productivity. This measure for various major foodstuffs is shown in the chart below. Values are expressed for one calendar year. Biological values and usable protein values have been added to the chart to show the true relative value of each foodstock for human consumption. Usable protein values are determined by the biological value (BV) of each foodstuff and represent the amount of protein that is fully digested by humans, it is calculated as follows:

Edible protein * BV = Usable protein

	Edible protein (g/m²)	Edible protein (lb/acre)	BV (%)	Usable protein (g/m²)	Usable protein (lb/acre)	Limiting amino acid	Notes
Soybeans	40.0	356	74	29	263	methionine	Soybeans produce at least two times as much usable protein per acre than any other major vegetable or grain crop, except for hemp which can produce up to 293 lbs of usable protein per acre (33 g/m²). They produce 5 to 10 times more protein per acre than land set aside for grazing animals to make milk, and up to 15 times more protein per acre than land set aside for meat production.[1]
Rice	29.0	260	86	25	224	lysine
Legumes (average)	22.0	192	49	11	94	tryptophan
Milk	9.2	82	91	8.4	75	methionine or cysteine
Wheat	15.0	138	54	8.1	75	lysine
Eggs	8.5	76	94	8.0	71
Maize	24.0	211	32	7.7	68	tryptophan
Meat (average)	5.0	45	80	4	36
Beef	2.2	20	78	1.72	15.6	phenylalanine or tyrosine

Selected averages as computed in the 1970s.^{[citation needed]}

In human nutrition

Further information: Protein in nutrition and Amino acid synthesis

When taken up into the human body from the diet, the 22 standard amino acids either are used to synthesize proteins and other biomolecules or are oxidized to urea and carbon dioxide as a source of energy.^[46] The oxidation pathway starts with the removal of the amino group by a transaminase, the amino group is then fed into the urea cycle. The other product of transamidation is a keto acid that enters the citric acid cycle.^[47] Glucogenic amino acids can also be converted into glucose, through gluconeogenesis.^[48]
Pyrrolysine trait is restricted to several microbes, and only one organism has both Pyl and Sec. Of the 22 standard amino acids, 9 are called essential amino acids because the human body cannot synthesize them from other compounds at the level needed for normal growth, so they must be obtained from food.^[49] In addition, cysteine, taurine, tyrosine, and arginine are considered semiessential amino-acids in children (though taurine is not technically an amino acid), because the metabolic pathways that synthesize these amino acids are not fully developed.^[50][51] The amounts required also depend on the age and health of the individual, so it is hard to make general statements about the dietary requirement for some amino acids.

Essential	Nonessential
Histidine	Alanine
Isoleucine	Arginine*
Leucine	Asparagine
Lysine	Aspartic acid
Methionine	Cysteine*
Phenylalanine	Glutamic acid
Threonine	Glutamine*
Tryptophan	Glycine
Valine	Ornithine*
	Proline*
	Serine*
	Tyrosine*

(*) Essential only in certain cases.^[52][53]

Classification of Amino Acids

Although there are many ways to classify amino acids, these molecules can be assorted into six main groups, on the basis of their structure and the general chemical characteristics of their R groups.

Class	Name of the amino acids
Aliphatic	Glycine, Alanine, Valine, Leucine, Isoleucine
Hydroxyl or Sulfur-containing	Serine, Cysteine, Threonine, Methionine
Cyclic	Proline
Aromatic	Phenylalanine, Tyrosine, Tryptophan
Basic	Histidine, Lysine, Arginine
Acidic and their Amide	Aspartate, Glutamate, Asparagine, Glutamine

Essential amino acid

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An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism (usually referring to humans), and therefore must be supplied in the diet.

Contents 1 Essentiality vs. conditional essentiality in humans 2 Recommended daily amounts 3 Use of essential amino acids 4 Essential amino acid deficiency 5 Mnemonics 6 See also 7 References 8 External links

Essentiality vs. conditional essentiality in humans

Essential	Nonessential **
Histidine	Alanine
Isoleucine	Arginine*
Leucine	Aspartic acid
Lysine	Cysteine*
Methionine	Glutamic acid
Phenylalanine	Glutamine*
Threonine	Glycine*
Tryptophan	Proline*
Valine	Serine*
	Tyrosine*
	Asparagine*
	Selenocysteine

(*) Essential only in certain cases.^[1][2]
(**) Pyrrolysine, sometimes considered "the 22nd amino acid", is not listed here as it is not used by humans. ^[3]
The amino acids regarded as essential for humans are phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, leucine, lysine, and histidine.^[4] Additionally, cysteine (or sulphur-containing amino acids), tyrosine (or aromatic amino acids), and arginine are required by infants and growing children.^[5][6] Essential amino acids are "essential" not because they are more important to life than the others, but because the body does not synthesize them. They must be present in the diet or they will not be present in the body. In addition, the amino acids arginine, cysteine, glycine, glutamine, histidine, proline, serine and tyrosine are considered conditionally essential, meaning they are not normally required in the diet, but must be supplied exogenously to specific populations that do not synthesize them in adequate amounts.^[1][2] An example would be with the disease phenylketonuria (PKU). Individuals living with PKU must keep their intake of phenylalanine extremely low to prevent mental retardation and other metabolic complications. However, they cannot synthesize tyrosine from phenylalanine, so tyrosine becomes essential in the diet of PKU patients.
The distinction between essential and non-essential amino acids is somewhat unclear, as some amino acids can be produced from others. The sulfur-containing amino acids, methionine and homocysteine, can be converted into each other but neither can be synthesized de novo in humans. Likewise, cysteine can be made from homocysteine but cannot be synthesized on its own. So, for convenience, sulfur-containing amino acids are sometimes considered a single pool of nutritionally-equivalent amino acids as are the aromatic amino acid pair, phenylalanine and tyrosine. Likewise arginine, ornithine, and citrulline, which are interconvertible by the urea cycle, are considered a single group.

Recommended daily amounts

Estimating the daily requirement for the indispensable amino acids has proven to be difficult; these numbers have undergone considerable revision over the last 20 years. The following table lists the WHO recommended daily amounts currently in use for essential amino acids in adult humans, together with their standard one-letter abbreviations.^[6]

Amino acid(s)	mg per kg body weight	mg per 70 kg	mg per 100 kg
H Histidine	10	700	1000
I Isoleucine	20	1400	2000
L Leucine	39	2730	3900
K Lysine	30	2100	3000
M Methionine + C Cysteine	10.4 + 4.1 (15 total)	1050	1500
F Phenylalanine + Y Tyrosine	25 (total)	1750	2500
T Threonine	15	1050	1500
W Tryptophan	4	280	400
V Valine	26	1820	2600

The recommended daily intakes for children aged three years and older is 10% to 20% higher than adult levels and those for infants can be as much as 150% higher in the first year of life.

Use of essential amino acids

At the level of the ribosome, the cells of eukaryotes require up to 21 different amino acids for protein synthesis. A shortfall of any one of these amino acids would thus be a limiting factor in protein synthesis. However, eukaryotes can synthesize some of these amino acids from other substrates. Consequently, only a subset of the amino acids used in protein synthesis are essential nutrients. Whether a particular amino acid is essential depends upon the species and the stage of development.
Scientists had known since the early 20th century that rats could not survive on a diet whose only protein source was zein, which comes from maize (corn), but recovered if they were fed casein from cow's milk. This led William Cumming Rose to the discovery of the essential amino acid threonine.^[7] Through manipulation of rodent diets, Rose was able to show that ten amino acids are essential for rats: lysine, tryptophan, histidine, phenylalanine, leucine, isoleucine, methionine, valine, and arginine, in addition to threonine. Rose's later work showed that eight amino acids are essential for adult human beings, with histidine also being essential for infants. Longer term studies established histidine is also essential for adult humans.^[8]
Because of the obvious difference in the nutritional value of zein versus casein in rat nutrition, various attempts have been made to express the "quality" or "value" of various kinds of protein. Measures include the biological value, net protein utilization, protein digestibility-corrected amino acid score. These concepts are important in the livestock industry, because the relative lack of one or more of the essential amino acids in animal feeds would have a limiting effect on growth and thus on feed conversion ratio. Thus, various feedstuffs may be fed in combination to increase net protein utilization, or a supplement of an individual amino acid (methionine, lysine, threonine, or tryptophan) can be added to the feed.
Although proteins from plant sources tend to have a relatively low biological value, in comparison to protein from eggs or milk, they are nevertheless "complete" in that they contain at least trace amounts of all of the amino acids that are essential in human nutrition.^[9] Eating various plant foods in combination can provide a protein of higher biological value.^[10] Certain native combinations of foods, such as corn and beans, soybeans and rice, or red beans and rice, contain the essential amino acids necessary for humans in adequate amounts.^[11]

Essential amino acid deficiency

The amino acids that are essential in the human diet were established in a series of experiments led by William Cumming Rose. The experiments involved elemental diets to healthy male graduate students. These diets consisted of cornstarch, sucrose, butterfat without protein, corn oil, inorganic salts, the known vitamins, a large brown "candy" made of liver extract flavored with peppermint oil (to supply any unknown vitamins), and mixtures of highly purified individual amino acids. The main outcome measure was nitrogen balance. Rose noted that the symptoms of nervousness, exhaustion, and dizziness were encountered to a greater or lesser extent whenever human subjects were deprived of an essential amino acid.^[12]
Essential amino acid deficiency should be distinguished from protein-energy malnutrition, which can manifest as marasmus or kwashiorkor. Kwashiorkor was once attributed to pure protein deficiency in individuals who were consuming enough calories ("sugar baby syndrome"). However, this theory has been challenged by the finding that there is no difference in the diets of children developing marasmus as opposed to kwashiorkor.^[13]

	FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS	ESN: FAO/WHO/UNU EPR/81/31 August 1981
	WORLD HEALTH ORGANIZATION
	THE UNITED NATIONS UNIVERSITY

Provisional Agenda Item 3.2.3

Joint FAO/WHO/UNU Expert Consultation on
Energy and Protein Requirements

Rome, 5 to 17 October 1981

AMINO ACID SCORING PATTERNS

by

A. Harper
University of Wisconsin
USA

This paper represents an effort to explain the differences between the amino acid scoring patterns for evaluating proteins proposed by the FAO/WHO Expert Committee that met in 1971 (1) and the Food and Nutrition Board Committee on Amino Acids (USA) which considered this subject as part of its project on assessment of the merit of amino acid fortification during the period between 1966 and 1971 (2). Both Committees used the same major sources of information about amino acid requirements of infants, adolescents and adults but there were a few differences in the way these were used and in the way they were supplemented with information about protein consumption and the amino acid composition of milk and other foods. As is indicated below, it was mainly the differences in the judgments of the Committees and in the sources of supplemental information that led to the somewhat different scoring patterns proposed by the two Committees.
The approach taken in dealing with this subject is to compare the estimates of amino acid requirements of adults, adolescents and infants as reported by the two Committees, pointing out differences in the values and, wherever it is possible, explanations for these. The provisional scoring patterns will then be compared and an effort will be made to identify reasons for differences between them and to assess the significance of these differences.
Amino Acid Requirements of Adults
Both Committees compiled values for amino acid requirements of adults from the studies of men by Rose and associates (3); of women by Leverton and associates (4); and from a few other studies that supplemented these (5–8), together with an analysis of the available information by Hegsted (9).
The values compiled by the two Committees are presented in Tables 1 and 2. Table 1 is from the FAO/WHO report (Table 17, p. 55). Table 2 is from the NRC report (Table 6, p. 40). The values selected for men by the two Committees (column 1 of Table 1 and column 5 of Table 2) are identical except for the requirement for total sulfur-containing amino acids for which the NRC Committee selected the lower value of 1010 mg/day obtained by Rose and Wixom (6) when they included both methionine and cystine, rather than methionine alone, in the experimental diets of their subjects. The values for women (column 2 of Table 1 and column 1 of Table 2) selected by the NRC Committee were the highest values for any individual, to conform with the procedure used by Rose. Thus the NRC value of 700 mg/day for total sulfur-containing amino acids exceeds that of 550 mg/day selected by the FAO/WHO Committee. The higher values selected by the FAO/WHO Committee for leucine and lysine requirements of females represent differences in the judgments of the two Committees as to the highest individual value for achievement of nitrogen equilibrium. Values for the amino acid requirements of women from the re-evaluation published by Hegsted (9) were included in both reports and (column 3 of both Tables 1 and 2) are identical.

Table 1. ESTIMATED AMINO ACID REQUIREMENTS OF ADULTS*

Amino acid	Some reported amino acid requirements (mg per day)			Combined adult value d (mg per kg per day)	Suggested pattern e (mg per g protein)
	Men a	Women
		Observed b	Recalculated c
Histidine	0	0	0	0	0
Isoleucine	700	450	550	10	18
Leucine	1 100	710	730	14	25
Lysine	800	700	545	12	22
Methionine + cystine	1 100	550	700	13	24
Phenylalanine + tyrosine	1 100	700	-	14	25
Threonine	500	310	375	7	13
Tryptophan	250	160	168	3.5	6.5
Valine	800	650	622	10	18

^a Taken from Rose.¹²⁰ The values represent the highest estimate of individual requirement to achieve positive nitrogen balance.
^b Taken from Leverton, Swendseid, Jones, Reynolds, Clark, Linksweiler, Burrill and their coworkers (the references have been summarized by Irwin & Hegsted ¹²¹). The values represent the highest estimate of individual requirement to achieve the zone of nitrogen equilibrium (balance of0 = 5% of intake).
^c Data of some of the above authors recalculated by Hegsted ¹²² using regression analysis to estimate the average requirement to achieve nitrogen equilibrium.
^d Derived estimate emphasizing the upper range of individual requirements.
^e Assuming a safe level of protein intake of 0.55 g per kg per day (averaged value for men and women).
*Table 17, FAO/WHO (1), p. 55.

Table 2. AMINO ACID REQUIREMENTS OF MAN (mg/kg/day)*

	Adultsc,d,e
	Female (58 kg)				Male (70 kg)
Amino acid	mg/day	mg/kg	mg/day	mg/kg	mg/day	mg/kg
His	?	?	?	?	?	?
lle	450	7.8	550	9.5	700	10.1
	(250–450)				(650–700)
Leu	620	10.7	725	12.5	1,100	15.7
	(170–620)				(500–1,100)
Lys	500	8.6	545	9.4	800	11.4
	(400–500)				(400–800)
Met	700f	12.1	700	12.1	1,100	15.7
	(300–700)				(800–1,100)
Cys	-	-	-	-	-	-
TSAAj	700	12.1	700	12.1	1,010g	14.4
					(910–1,010)
Phe	700h	12.1	700	12.1	1,100	15.7
	(600–700)				(800–1,100)
Tyr	-	-	-	-	-	-
TAAAj	700	12.1	700	12.1	1.100i	15.7
Thr	305	5.3	375	6.5	500	7.1
	(103–305)				(300–500)
Trp	160	2.8	168	2.9	250	3.6
	(82–157)				(150–250)
Val	650	11.2	622	10.7	800	11.4
	(465–650)				(400–800)
Total	-	-	-	76	-	91

^cLeverton, 1959.
^dHegsted, 1963.
^eRose, 1957.
^fReynolds et al. 1958.
^gRose and Wixom, 1955c. Cys will spare 80–89 percent of the Met requirement.
^hBurrill and Schuck, 1964.
ⁱRose and Wixom, 1955c. Tyr will spare 70–75 percent of the Phe requirement.
^jTSAA is total sulfur-containing amino acids; TAAA is total aromatic aminoacids.
* From Table 6, NRC (2), p. 40.
The FAO/WHO Committee averaged the adult values expressed as mg/kg of body wt/day and derived an amino acid scoring pattern for adults (column 5 of Table 1). This was based on the assumption that the amounts of individual amino acids required (column 4 of Table 1) should be provided by 0.55 g of protein, the estimated safe level of intake of high quality protein. The NRC Committee did not propose an amino acid scoring pattern for adults. It did, however, select the set of requirements for adults estimated from the re-evaluation by Hegsted, as probably the most reliable set of values after reviewing the entire published data. Both Committees concluded that the apparent sex difference between requirements of males and females was not significant.
Differences between the two sets of requirements (columns 4 of Tables 1 and 2) are not great. The NRC estimate for the lysine requirement is low; the higher FAO estimate is largely attributable to the particularly high value for males from the experiments of Rose in which the highest value for a single subject was accepted as the requirement. The somewhat higher estimates for leucine and total aromatic amino acid requirements in the FAO/WHO report are similarly explained.
Both Committees pointed out that the estimates of amino acid requirements are from nitrogen balance studies and did not take into account integumental and other minor nitrogen losses or the additive errors of the balance technique, so probably underestimate somewhat the actual requirements. Values calculated by Hegsted to be required for positive nitrogen retention of 0.5 gm/day were much higher than the values determined from regression analysis of requirements for nitrogen equilibrium. They were considered, by the NRC Committee, to be unrealistic as there were far too few values at the upper end of the requirement range to permit identification of an inflection point in the regression line on which the analysis was based.
Amino Acid Requirements of Children
Both Committees compiled values for amino acid requirements of children, aged 10–12 years, from the publications of Nakagawa et al. (10–15). The FAO/WHO Committee accepted values from the publications of Nakagawa et al. for the upper range of individual requirements for achievement of positive nitrogen balance (Table 3). The NRC Committee recognized that Nakagawa et al. had used rather large increments of amino acids in estimating requirements, that some of the values for requirements were not proportional to either the adult or infant requirements and that Snyderman (16) had observed a decline in phenylalanine requirement by 18 months to less than one-third of the requirement at birth (Figure 1). The NRC Committee, therefore, estimated requirements for children from the information about individual subjects given in the published reports (Table 4). These values are, without exception, lower than those accepted by the FAO/WHO Committee. The validity of this approach may be open to question; nevertheless, the values, with the exceptions of the requirements for phenylalanine and tryptophan which seem inordinately low, are more in line with those for the infant if it is assumed that other requirements fall at about the same rate as that for phenylalanine (16).

Table 3. ESTIMATED AMINO ACID REQUIREMENTS OF CHILDREN*

Amino acid	Schoolchildren, 10–12 years
	Observed requirement a (mg per kg per day)	Suggested pattern b (mg per g of protein)
Histidine	0	0
Isoleucine	30	37
Leucine	45	56
Lysine	60	75
Methione + cystine	27	34
Phenylalanine + tyrosine	27	34
Threonine	35	44
Tryptophan	4	4.6
Valine	33	41

^a Based on Nakagawa et al.^125–126 The values represent estimates of the upper range of individual requirements for the achievement of positive nitrogen balance in boys.
^b Based on a safe level of protein intake of 0.8 g per kg per day, the average of safe levels of protein for boys and girls in that age group.
* Table 18, FAO/WHO (1), p. 56.

Table 4. AMINO ACID REQUIREMENTS*

	Children (10–12 yr; 36 kg)b
Amino acid	mg/day	mg/kg
His	?	?
Ile	1,000	28
Leu	1,500	42
Lys	1,600	44
Met	800	22
Cys	-	-
TSAAj	800	22
Phe	800	22
Tyr	-	-
TAAAj	800	22
Thr	1,000	28
Trp	120	3.3
Val	900	25
Total	-	288

^b Nakagawa et al., 1960, 1961a,b, 1962, 1963, 1964.
* From Table 6, NRC (2), p. 40.
FIGURE 1. The phenylalanine requirement of the phenylketonuric infant related to age; average of 50 infants and one standard deviation above and below the average (Snyderman, 1974).
The FAO/WHO Committee calculated an amino acid scoring pattern for children based on the assumption that the safe level of intake of high quality protein for this age group is 0.8 gm/kg of body wt/day. It is noteworthy that the values per gm of protein for lysine and total sulfur-containing amino acids in this pattern are higher than those for the infant.
Amino Acid Requirements of Infants
Both Committees tabulated the amino acid requirements of infants, as estimated by Holt and Snyderman (17). The values in column one of Tables 5 and 6 are in agreement with the exception of that for leucine. The lower value reported by the NRC Committee for the leucine requirement was provided by Dr. L. E. Holt, Jr. from a study done after the earlier report used by the FAO/WHO Committee.
Both Committees also estimated amino acid requirements of infants from the amounts of protein consumed by infants fed on formulas and who were growing well in studies done in the Pediatrics Department at the University of Iowa (18, 19). The values reported by the two Committees are quite different (column 2 in Table 5 and column 4 in Table 6). The FAO/WHO Committee used values estimated by Foman and Filer (19). The NRC Committee calculated intakes of amino acids of infants fed three different formulas from the published nitrogen intakes (18) using values for amino acid composition of foods compiled by Orr and Watt (20). The lowest value from among the three estimates was accepted as the requirement. With the exception of the requirement for tryptophan, the values estimated from the amounts of protein consumed in formulas were lower than those estimated by Holt and Snyderman. It should be recognized that infants in the studies by Holt and Snyderman were as young as two months of age whereas those studied by Foman and associates were 4.5 to 6 months of age.

Table 5. ESTIMATED AMINO ACID REQUIREMENTS OF INFANTS*

Amino acid	Estimated requirements		Composite of lower values (mg per kg per day)	Suggested pattern c (mg per g of protein)
	Holt & Synderman a (mg per kg per day)	Fomon & Filer b (mg per kg per day)
Histidine	34	28	28	14
Isoleucine	119	70	70	35
Laucine	229	161	161	80
Lysine	103	161	103	52
Methionine + cystine	45 + Cys	58 d	58	29
Phenylalanine + tyrosine	90 + Tyr	125 d	125	63
Threonine	87	116	87	44
Tryptophan	22	17	17	8.5
Valine	105	93	93	47

^a Requirements estimated when amino acids were fed or incorporated in basal formulas. The values represent estimates of maximal individual requirements to achieve normal growth. ^123
b Calculated intakes of amino acids when formulas were fed in amounts sufficient to maintain good growth in all the infants studied; the amino acids were not varied independently. ^124
c Based on a safe level of intake of 2 g protein per kg per day, the average of suggested levels for the period 0–6 months.
^d The values for cystine and tyrosine were estimated on the basis of the methionine: cystine and phenylalanine: tyrosine ratios in human milk (see Table 20).
* Table 18, FAO/WHO (1), p. 56.

Table 6. AMINO ACID REQUIREMENTS*

	Infants (2–6 mo)a
Amino acid	mg/kg
His	34
Ile	119
Leu	150
Lys	103
Met	45
Cys	80
TSAAj	125
Phe	90
Tyr	present
TAAAj	?
Thr	87
Trp	22
Val	105
Total	835

^aHolt and Snyderman, 1965.
* From Table 6, NRC(2), P. 40.

Table 7. ESSENTIAL AMINO ACID INTAKES OF INFANTS WITH SATISFACTORY WEIGHT GAIN*

	Milk or Formula (Fomon, 1961 a)
	Human Milk	Cow's Milk	Soybean Formula	Minimum by Method of Harte and Travers (1947)
Protein intakec (g/kg)	1.50	1.46	1.73
N intake (g/kg)	0.24	0.23	0.28
Amino acid (mg/kg)
His	33	39	42	33
Ile	83	94	94	83
Leu	136	144	135	135
Lys	99	114	111	99
Met	31	36	24	36
Cys	30	13	31	13
TSAA	61	49	55	49
Phe	65	71	87	65
Tyr	76	75	56	76
TAAA	141	146	143	141
Thr	68	68	69	68
Trp	25	21	24	21
Val	94	101	92	92

*From Table 8, NRC (2), p. 46.
With respect to the differences in the estimated requirements of infants consuming formulas reported by the two Committees, it should be noted that a later set of requirement values reported by Fomon (21) are much more in line with those of the NRC Committee. A comparison of the earlier values and the later ones is given in Table 8.

Table 8. AMINO ACID REQUIREMENTS OF INFANTS

	Foman & Filer 1967 mg/kg/day	Foman 1974 mg/100 kcal
Histidine	28	26
Isoleucine	70	66
Leucine	161	132
Lysine	161	101
Methionine + cystine	58	47
Phenylalanine + tyrosine	125	57 + tyr
Threonine	116	59
Tryptophan	17	16
Valine	93	83

It should also be noted that Snyderman and associates (22) were able to maintain satisfactory rates of growth in a small group of infants who consumed a cow's milk formula that was diluted and to which was added glycine and urea. These infants were consuming amounts of amino acids slightly below those estimated to be adequate from the studies of Foman and associates (column 4 of Table 7).
Amino Acid Scoring Patterns
The amino acid scoring patterns for different age groups suggested by the FAO/WHO Committee are presented in Table 9 together with patterns proposed by earlier FAO/WHO Expert Committees (23, 24). Similar information from the NRC Committee Report is presented in Table 10.
In assessing the earlier amino acid scoring patterns, it should be recalled that information about amino acid requirements of infants had not been published in 1957 when the first FAO scoring pattern was proposed. This pattern was based mainly on the amino acid requirements of adults. The values are essentially double those of the pattern proposed for adults by the FAO/WHO Committee in 1973. It became evident subsequently, particularly from observations that infants consuming cow's milk formula grew well, that the value for sulfur-containing amino acids in the 1957 pattern was high.
The 1965 FAO/WHO Expert Committee did not propose an amino acid scoring pattern based on studies of amino acid requirements but, instead, proposed that the amino acid patterns of human milk, cow's milk or whole egg could serve this purpose. The agreement among the values for the amino acid compositions of these proteins reported in the 1973 FAO/WHO and 1974 NRC reports is striking, considering that the values were from different sources. The low value for the total aromatic amino acid content of human milk in the FAO/WHO report (column 6 in Table 9) is undoubtedly a transcription error and should be 92 rather than 72. The value for the isoleucine content of cow's milk (column 7 of Table 9) appears to be low. The one disturbing feature is the range of values reported by the FAO/WHO Committee for the amino acid composition of human milk. This would suggest that human milk proteins can range between 40 and 60% in their content of essential amino acids. The lower end of this range would be close to that expected in plant proteins; the upper end would exceed that of animal proteins generally.

Table 9. COMPARISON OF SUGGESTED PATTERNS OF AMINO ACID REQUIREMENTS WITH THE COMPOSITION OF MILK AND EGG PROTEIN* (mg per g of protein)

Amino acid	Suggested patterns of requirement a			1957 FAO pattern	Reported composition
	Infant	School-child 10–12 years	Adult		Human milk		Cow's milk c	Egg d
					Range b	Mean
Histidine	14	-	-	-	18– 36	26	27	22
Isoleucine	35	37	18	42	41– 53	46	47	54
Leucine	80	56	25	48	83–107	93	95	86
Lysine	52	75	22	42	53– 76	66	78	70
Methionine + cystine	29	34	24	42	29– 60	42	33	57
Phenylalanine + tyrosine	63	34	25	56	68–118	72	102	93
Threonine	44	44	13	28	40– 45	43	44	47
Tryptophan	8.5	4.6	6.5	14	16– 17	17	14	17
Valine	47	41	18	42	44– 77	55	64	66
Total
+ histidine	373				408–588	460	504	512
- histidine		326	152	314	390–552	434	477	490

^a See preceding tables.There is no evidence for or against a histidine requirement for young children.
^b Compositions reported by FAO,¹⁴ Lindner et al.,³³ and Soupart et al.^129
c Composition reported by FAO;¹⁴ value for tryptophan by microbiological assay.
^d Composition reported by Lunven et al.¹³⁶
*Table 20, FAO/WHO, p. 58.

Table 10. AMINO ACID PATTERNS PROPOSED FOR EVALUATING NUTRITIONAL QUALITY OF PROTEINS (mg/g) *

Amino Acid	FAO 1957	FAO 1965		Cow's Milka	Minimum (Cols. 2–4)	Proposed Pattern
		Human Milka	Egga
His		22	24	27	22	17
Ile	42	55	66	65	55	42
Leu	48	91	91	100	91	70
Lys	42	66	66	80	66	51
TSAA	42	41	55	34	34	26
TAAA	56	95	101	100	95	73
Thr	28	45	50	47	45	35
Trp	14	16	18	14	14	11
Val	42	62	74	70	62	48
Total	314	493	545	537	484	373

^aOrr and Watt, 1968.
* Table 11, NRC, p. 56.
The proposal that the amino acid compositions of these proteins could serve as guides for amino acid scoring of proteins posed new problems. The value for total sulfur-containing amino acids in cow's milk is well below that of the 1957 scoring pattern but the value for egg proteins greatly exceeded that of the 1957 pattern. Also, the values for lysine for all three proteins were well above that of the 1957 pattern, particularly those of cow's milk and egg.
The efforts of the most recent FAO/WHO Expert Committee and the NRC Committee to remedy these problems culminated in proposals for new amino acid scoring patterns. That proposed by the NRC Committee is presented in the last column of Table 10 and that proposed by the FAO/WHO Committee is presented in Table 11. Both Committees concluded that the scoring patterns should be designed for evaluating the adequacy of proteins for the young child and that they should be based mainly on the estimated amino acid requirements of infants. The proposed patterns are expressed as mg of amino acid per gram of protein. The amino acid values were selected so that a protein having an amino acid composition matching or exceeding the scoring pattern should meet the requirements for all of the essential amino acids when it is fed in an amount that will meet the total requirement for high quality protein.

Table 11. PROVISIONAL AMINO ACID SCORING PATTERN*

Amino acid	Suggested level
	mg per g of protein	mg per g of nitrogen
Isoleucine	40	250
Leucine	70	440
Lysine	55	340
Methionine + cystine	35	220
Phenylalanine + tyrosine	60	380
Threonine	40	250
Tryptophan	10	60
Valine	50	310
Total	360	2 250

*Table 21, FAO/WHO, p. 63
The approach used by the NRC Committee was to select for the scoring pattern values per gram of protein that were about half those of the infant amino acid requirements per kg of body weight. Two grams per kg of such a protein, the estimated requirement of the infant for high quality protein, would thus provide enough of each of the essential amino acids to meet the estimated amino acid requirements of the infant. Then, as amino acid requirements fall more rapidly with age than the protein requirement, such proteins should be more than adequate in essential amino acid content for other age groups.
The FAO/WHO Committee used essentially the same procedure but took into account the estimated amino acid requirements for both infants and young children. It also considered the amounts of amino acids consumed from foods by young children who were growing normally. It also rounded off all of the values, except that for tryptophan, to the nearest 5 mg.
As the result of these somewhat different procedures, there are some differences in the proposed patterns. The values for isoleucine, leucine, tryptophan and valine are practically the same in both patterns. The value for lysine is about 8% higher in the FAO/WHO pattern; this is the result of using the slightly higher estimate of the requirement for lysine from Holt and Snyderman and rounding off the value to the next highest 5 mg. The value for total aromatic amino acids in the FAO/WHO scoring pattern is 18% below that of the NRC pattern. This is attributable to the lower value for the requirement for total aromatic amino acid requirements of infants selected by the FAO/WHO Committee from the review article by Foman and Filer whereas the NRC Committee selected the higher values calculated from intakes by infants fed three different formulas (compare column 2 in Table 5 with column 4 in Table 7). The value for threonine in the FAO/WHO pattern is 14% higher than that in the NRC pattern. This is attributable to use of the higher value for the threonine requirement of infants reported by Holt and Snyderman by the FAO/WHO Committee as compared to the lower value from estimates of threonine intakes by infants fed various formulas and growing well selected by the NRC Committee (compare column 1 in Table 5 with column 4 in Table 7).
The value for total sulfur-containing amino acids shows the greatest discrepancy. The FAO/WHO value is 34% higher than that selected by the NRC Committee. The FAO/WHO Committee used the estimated requirement for young children as the basis for this value rather than the infant requirement which was lower per gram of protein (compare the last columns of Tables 3 and 5). The NRC Committee concluded that this value was high on the basis of a re-evaluation of the information in the original paper.
The major difference between the two amino acid scoring patterns that is of some concern is that between the values for methionine plus cystine. This subject has been reviewed (25, 26) since the two committee reports were published and some additional information (27–29) on amino acid requirements of young children that bears both specifically on the requirement for methionine plus cystine and also on amino acid requirements more generally, has since become available.
It was pointed out above that, in establishing the pattern of amino acid requirements of infants, the FAO/WHO Expert Committee used values for amino acid intakes of infants published in a review article in 1967 by Fomon and Filer (19) and that these did not agree well with values published subsequently in 1974 by Fomon (21). Harper (26), therefore, recalculated the values for amino acid intakes of infants in the studies by Fomon and associates, using the FAO/WHO values for protein intakes by infants fed cow's milk formulas (Table 15 in the 1973 FAO/WHO report) and the FAO/WHO values for amino acid composition of milk as given in Table 9 (Table 20 of the FAO/WHO Report). The results of these calculations are shown in Table 12. If the recalculated values based on protein intakes (given in parentheses in column 3 of Table 12) are substituted for the respective values in the FAO/WHO estimates of requirements (Table 12, column 3), and also in the FAO/WHO proportionality pattern (Table 12, column 5), differences between the NRC and FAO/WHO tabulations would be small. It should be noted that the proportionality patterns in Table 12 are not the final amino acid scoring patterns selected by either the NRC Committee or the FAO/WHO Committee.
Fomon et al. (27) have published information on methionine intakes of infants who grew well while they were being fed a soybean protein formula with or without a supplement of methionine. These infants were observed over the period of growth from 8 to 111 days of age. They were thus younger than most of the infants in other studies of amino acid requirements. The intakes of total sulfur-containing amino acids for the period between 42 and 111 days of age were, for the supplemented group 57.6 mg/100 kcal and for the unsupplemented group 50.7 mg/100 kcal. The two groups consumed 102 and 106 kcal/kg/day, respectively, during this period. Nitrogen retentions of the two groups were similar. The methionine-supplemented group had slightly higher serum albumin and slightly lower serum urea concentrations than the unsupplemented group during the early part of the experiment. What is noteworthy is that these young infants who were growing well had methionine plus cystine intakes slightly below the FAO/WHO, and slightly above the NRC, estimated requirements for infants 4.5 to 6 months of age. The requirements for the older infants should be lower, as requirements fall with increasing age. This comparison would seem to indicate, however, that the requirement for the sulfur-containing amino acids of infants falls less rapidly than that for the aromatic amino acids with increasing age. The same would be true for older age groups (2) if the estimates of requirements for sulfur-containing amino acids of adolescents (Tables 3 and 4) and adults (Tables 1 and 2) are accepted (see also column 5 of Table 13, below).
Quite recently information about amino acid requirements of 2-year old children has been reported from INCAP (28, 29). The children studied were fed a diet containing a low level of protein with additional nitrogen from an amino acid mixture so the dietary level of each amino acid in turn could be altered readily while total “protein” intake was kept constant. Growth, nitrogen retention and several biochemical indicators were monitored. From measurements of amino acid intakes to maintain satisfactory performance, estimates of amino acid requirements were made. These (28, 29) are given in column 2 of Table 13 together with the NRC estimates of requirements per kg of body weight per day for other age groups (Tables 2,4 and 6).

Table 12. COMPARISON OF VALUES FOR AMINO ACID REQUIREMENTS OF INFANTS*

	Estimated Amino Acid Requirements			Proportionality Pattern1
	Holt and Snyderman	Based on Milk Protein Intake		NAS/NRC	FAO/WHO
		NAS/NRC	FAO/WHO
	mg/kg body wt/day			mg/gm of protein
Histidine	34	33	28 (39)3	17	14 (19)3
Isoleucine	119	83	70	42	35
Leucine	150 (229)2	135	161 (140)	68	80 (70)
Lysine	103	99	161 (99)	50	52 (50)
Met + cys	45 + cys	49	58 (50)	25	29 (25)
Phe + Tyr	90 + tyr	141	125	70	63
Threonine	87	68	116 (66)	34	44 (33)
Tryptophan	22	21	17 (21)	11	8.5 (11)
Valine	105	92	93	46	47

¹ Assuming protein requirement is 2 gm/kg body wt/day.
² FAO/WHO report (2).
³ Figures in parentheses calculated from average values for milk composition in Table 20 of FAO/WHO report (2).
^* Table 2 from reference 26.

Table 13. CHANGE IN AMINO ACID REQUIREMENTS WITH AGE

	Infants (4.5–6 mo)	Children (2 yr)	Children (10–12 yr)	Adults Requirement	Adult as % of Infant
	milligrams/kilogram of body weight/day
Histidine	33	?	?	?	-
Isoleucine	83	31	28	9.5	11.4
Leucine	135	73	42	12.5	9.3
Lysine	99	64	44	9.4	9.5
Methionine + cystine	49	27	22	12.1	25.0
Phenylalanine + tyrosine	141	69	22	12.1	8.6
Threonine	68	37	28	6.5	9.6
Tryptophan	21	14	3.3	2.9	13.8
Valine	92	43	25	10.7	11.6

From these estimates, the amino acid requirements, with the exceptions of those for lysine and tryptophan, would appear to decline by about 50% between 6 months and 2 years of age. This is about the same rate of decline (Figure 1) as was reported by Snyderman (16) for the phenylalanine requirement and is somewhat greater than the estimated decline in the protein requirement (1, 2).
The question that still remains to be settled is: “What is the appropriate amino acid scoring pattern for evaluating dietary proteins?” The proposed scoring patterns are listed in Table 14. The INCAP values have been calculated per gram of protein from the information on amino acid requirements presented by Pineda et al. (28).

Table 14. PROVISIONAL AMINO ACID SCORING PATTERNS

	FAO/WHO	NRC	INCAP
	mg/gm of protein
Histidine	-	17	-
Isoleucine	40	42	27
Leucine	70	70
Lysine	55	51	55
Methionine + cystine	35	26	24
Phenylalanine + tyrosine	60	73
Threonine	40	35	32
Tryptophan	10	11	12
Valine	50	48	33

The values derived from the INCAP studies for valine and isoleucine are considerably lower than those proposed by either Committee; the values for lysine and tryptophan do not deviate greatly from those of the provisional patterns. As the INCAP values are based on studies of two-year olds who should have lower amino acid requirements than younger children per unit of body weight, although not necessarily per gram of protein, it would seem unwise to lower the values for valine and isoleucine on which the two Committees agreed well, particularly as the scoring pattern was meant to apply for children younger than 2 years of age. The values for amino acids other than lysine are not greatly different from the NRC values. Pineda et al. (28) indicated that the INCAP tryptophan value may be an overestimate. From examination of Table 12, it would appear that the two Committees may have been in closer agreement than the proposed scoring patterns would suggest, if the recalculated values given there are accepted. If consideration is to be given by FAO/WHO to revising the amino acid scoring pattern, it would seem wise to review critically the information discussed in relation to this table.
In relation to the question of sulfur-containing amino acid requirements, the information presented by the INCAP group (28, 29) and that of Fomon et al. (29 and earlier studies) should be reviewed carefully. The analysis presented here would indicate that the FAO/WHO value for methionine plus cystine is high. The INCAP and NRC reports also support this view. Interestingly the pattern proposed by the NRC Committee resembles closely that of cow's milk (25), with which Fomon and associates (1, 2) observed satisfactory growth rates of 4.5 to 6-month old infants consuming only 1.5 gm of protein per kg of body weight per day. These observations also support the validity of a lower value for total sulfur-containing amino acids than that in the present FAO/WHO amino acid scoring pattern.