营养素知识: Protein

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营养素名称: Protein  
营养素类别: Macronutrients (Proximates)
计量单位: g
Protein is fundamental for body cell structure, and it is also extremely important for many body processes, such as acting as enzymes, production of hormones, transportation of nutrients, blood clotting, body fluid balance, acid-base balance, immune response (antibodies) to protect from virus infection, and eye vision. Proteins also provide calories ("energy") for the body.

营养素功效

As Structure Material:

  • Protein is the major structural component of all body cells. Proteins are used to build and repair body cells and tissues.
  • Protein is an integral part of muscle, skin, hair, nails, bone, collagen, internal organs, and even blood. Here are the protein distributions in a body: ~43% in muscle, ~15% in skin, ~15% in blood, ~10% in liver and kidney tissue, the remainders are in other organs and bone.

As Enzymes:

  • Some proteins act as enzymes. Enzymes are biological catalysts which facilitate and speed up specific chemical reactions. Enzymes are not changed during the reaction and used over and over.
  • Enzymes can break down substances, such as digestive enzymes. Some enzymes act as building up or synthesis reactions, such as building bones. And some enzymes can transform one substance to another, such as transforming amino acids into glucose for energy.

As Hormones:

  • Some hormones are proteins. Hormones are chemical messengers, they send signals into the bloodstream and tissues to coordinate and maintain normal body conditions and functions.

As Nutrients Transporters:

  • Some proteins act as transporters which carry nutrients and other molecules (such as lipids, vitamins, minerals, and oxygen) to move around in the body fluids. For example, the protein hemoglobin carries oxygen from the lungs to the cells. Some transport proteins carry vitamins and minerals.

As Antibodies:

  • When the body detects invading virus (antigens), its immune system generates antibodies which are giant protein molecules to combat antigens. The antibodies combine and inactivate the invaders antigens.
  • For each particular antigen, body generates the corresponding antibody to against it. More importantly, the body remembers how to make an antibody to against a specific antigen.

Role in Blood Clotting:

  • When a tissue is injured, insoluble mass of protein fibers, called fibrin, form a solid clot from liquid blood. Then slowly protein collagen forms a scar to heal the wound.

As a Source of Energy and Glucose:

  • As a source of energy, one gram of protein provides 4 calories, usually protein contributes 10-15% of daily calories needed.
  • When a person doesn't have sufficient carbohydrate and fat intake, the body will break down its tissue proteins to make amino acids available for energy or glucose production.

Protein is made up of 20 types of amino acids chained together. The amino acid sequences of proteins in the bodies are unique for each person. The instructions for the proteins amino acid sequences are based on DNA.

  • 9 Essential Amino Acids: they are required for normal body functioning, growth, maintenance, and repair. Bodies cannot make Essential Amino Acids (or don't make sufficient amount), they must be obtained from foods.
  • 11 nonessential amino acids: some foods contain these amino acids, but bodies can synthesize them from amino groups (NH2) and fragments from carbohydrate or fat. Some of nonessential amino acids conditionally become essential when the bodies cannot form them (or don't form enough of them) for any reason.

Body enzymes digest and break dietary proteins into individual amino acids and nitrogen. Then body makes its own needed proteins from these amino acids. So dietary proteins do not equal to body proteins.

Some of amino acids go to intestinal cells for energy, some of them are transported from intestinal across the cell membrane into the surrounding fluid for synthesizing needed compounds. The excessive amino acids are deaminated into ammonia (NH3) and keto acid. Two ammonia are combined with one carbon dioxide to form urea and are excreted via urine.


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食物来源

Proteins from animal meats:

  • Lean red meats: such as beef and pork
  • Poultry
  • Seafood: fish and shellfish
  • Eggs, milk
  • Milk and dairy products, such as cheese, and yogurt

Proteins from plants:

  • Soybeans and soy products: such as tempeh, tofu, veggie burgers.
  • Legumes (beans) and peas: such as soybeans, black beans, peanuts, etc.
  • Whole grains: such as oats, whole wheat flour, rice flour, quinoa, etc.
  • Nuts: such as peanuts, almond nuts, pistachio nuts, walnuts, etc.
  • Seeds: such as pumpkin seeds, sunflower seeds, chia seeds, etc.
  • Some vegetables: such as sprouted soybeans, bitter gourd, white mushroom, spinach.

Most plant foods contain only some types of amino acids, so you should take multiple types of plant foods containing different protein amino acids together to obtain a complete protein requirements. For example, black beans and rice provide different types of essential amino acids.

Protein Quality: The quality of the protein foods is determined by their digestibility during digestion and completeness of the essential amino acids.

  1. Protein Digestibility (absorption):

    • most animal proteins: between 90-99%
    • soybeans and other legumes: > 90%
    • other plants: 70-90%

  2. Amino Acid Coverage: cells need Amino Acids to make proteins.

    • 9 Essential Amino Acids must be obtained from foods, or by breaking down existing protein in the body. Animal foods and soybeans contain all the essential amino acids.
    • 11 non-essential amino acids can be made in the liver with certain types of amino acids.

  3. Amino Acid Composition: high quality proteins contains all the essential amino acids in similar amounts and proportions to what human beings require, such as foods from animals.

Bodies continuously break down dietary proteins and use them, however, bodies cannot store proteins or amino acids. So we need to intake proteins daily. 25-35 grams of high quality proteins at each meal may best support protein synthesis needs and maintain muscle health. Also make sure to intake sufficient carbohydrate and fat to provide adequate energy, otherwise, the intaken proteins will be used for energy instead of generating proteins the body needs.

富含营养素食物示例: Protein
查阅更多主要食物来源
食物描述 营养含量1 每日需量%2
Beef, round, bottom round, steak, separable lean and fat, trimmed to 1/8" fat, all grades, cooked, braised
类别: Beef Products
 32.76 g 65.52%
Pork, fresh, loin, tenderloin, separable lean only, cooked, broiled
类别: Pork Products
 30.42 g 60.84%
Chicken, broiler or fryers, breast, skinless, boneless, meat only, cooked, braised
类别: Poultry Products
 32.1 g 64.20%
Fish, tuna, fresh, bluefin, cooked, dry heat
类别: Finfish and Shellfish Products
 29.91 g 59.82%
Cheese, parmesan, low sodium
类别: Dairy and Egg Products
 41.6 g 83.20%
Egg, whole, cooked, fried
类别: Dairy and Egg Products
 13.61 g 27.22%
Soybeans, mature cooked, boiled, without salt
类别: Legumes and Legume Products
 18.21 g 36.42%
Peanuts, all types, oil-roasted, without salt
类别: Legumes and Legume Products
 28.03 g 56.06%
Oats (Includes foods for USDA's Food Distribution Program)
类别: Cereal Grains and Pasta
 16.89 g 33.78%
1 100克食物中的营养素含量
2 以FDA基于2000卡路里的饮食作为日需量参考



更多营养素信息
缺乏营养对健康的影响
Protein deficiency has been shown to affect all organs and many body systems and functions, including brain function, kidney function, immune system, and nutrient absorption ability.

From the physical characteristics view, protein deficiency may cause edema (swelling in part of the body), slow growth, poor musculature, dull skin, and thin and fragile hair.

To prevent protein deficiency, make sure to intake sufficient proteins based on the Recommended Daily Values for your corresponding age group. Also, to prevent protein-energy malnutrition, a person should keep good balance of energy calories sources. For adults, they are:

  • 10-35% from proteins
  • 45-65% from carbohydrates
  • 20-25% from total fat

Calories Calculation General Formula:
carbohydrate x 4 + protein x 4 + fat x 9
超过上限对健康的影响
Currently, there is no sufficient data to establish a Tolerable Upper Intake Level (UL) for total protein. Currently there is no evidence that amino acids derived from usual or even high intakes of protein from food present any risk. However, for amino acid dietary supplements, please be cautious when using any single amino acid dietary supplements in amounts significantly above what normally found in food.

Warning: potential problems with high protein intake:

  • Usually high protein animal meats contain high amount of saturated fats which may increase the risk of developing cardiovascular disease. Recommend to eat a variety of protein foods from animal and plant sources. For example, eat some seafoods to replace some red meats and poultry, drink low-fat milk, substitute legumes (especially soybeans) and nuts for animal protein.
  • When protein intake is high, calcium excretion increases. Bones need both protein and calcium for optimal growth.
  • High protein intake increases the work of the kidneys to excrete urea, in addition, it may also cause dehydration if not drinking enough water.
参考资料
更多信息
9 Essential Amino Acids:
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine


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日需量年龄组 每日需量建议
幼儿1至3岁: 13 g
儿童4至8岁: 19 g
男性9至13岁: 34 g
男性14至18岁: 52 g
男性19至30岁: 56 g
男性31至50岁: 56 g
男性51至70岁: 56 g
男性71岁或以上: 56 g
女性9至13岁: 34 g
女性14至18岁: 46 g
女性19至30岁: 46 g
女性31至50岁: 46 g
女性51至70岁: 46 g
女性71岁或以上: 46 g
女性孕妇(18岁以上): 71 g
女性哺乳期(18岁以上): 71 g
FDA（基于2000卡路里的日常饮食）: 50 g


Protein 与其他营养素的相互作用 
Magnesium, Mg
充足的蛋白质摄入量（不要太多或太少）可以改善镁的吸收和保留
蛋白质摄入量和蛋白质类型会影响镁的吸收。

  1. 摄入足够的蛋白质可以增强镁的吸收。蛋白质可以与镁形成可溶性复合物，它增加其在肠道中的生物利用度和吸收率。一些研究表明，动物蛋白中存在的某些氨基酸（如赖氨酸lysine）可能比植物蛋白更有效地增强镁的吸收。
  2. 过多的蛋白质可能会导致尿液中镁的排泄增加。
  3. 蛋白质不足可能会影响有助于镁吸收的转运蛋白 transport proteins 的形成。

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膳食参考摄入量 营养成分参考摄入量数据和营养成分知识来自于美国国立医学研究院2006年。膳食参考摄入量：营养需求基本指南。华盛顿特区:国家科学院出版社。National Academies' Institute of Medicine 2006. Dietary Reference Intakes: The Essential Guide to Nutrient Requirements. Washington, DC: The National Academies Press. https://doi.org/10.17226/11537
美国食品和药物管理局教育 营养成分知识基于美国食品和药物管理局（USFDA）营养教育资源文章。 https://www.accessdata.fda.gov/scripts/interactivenutritionfactslabel/
美国国立卫生研究院 营养成分知识基于美国国立卫生研究院的膳食补充剂情况说明书(Dietary Supplement Fact Sheets)。 https://ods.od.nih.gov/factsheets/list-all
免责声明 此处提供的营养信息不应取代医疗建议。我们鼓励您与您的医疗保健提供者（例如您的医生）讨论对您的整体健康最有利的饮食需求。我们还建议您阅读本页提及的，但不限于，组织机构或专业参考文选或文章。此页面中的任何提及和参考链接并不代表我们对其服务和建议的代言（endorsement）。


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