Nutrient Information: Protein

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Nutrient Key Information 
Nutrient Name: Protein
Nutrient Category: Macronutrients (Proximates)
Measuring Unit: g
Nutrient Summary: 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.
Nutrient Function: 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.

Protein Interactions With Other Nutrients 
Magnesium, Mg
Adequate protein intakes (not too much or too little) can improve magnesium absorption and retention
The amount and type of protein intake impacts magnesium absorption.

  1. Adequate protein intake can enhance magnesium absorption. Proteins can form soluble complexes with magnesium, which may increase its bioavailability and absorption in the intestines. Some studies suggest that certain amino acids present in animal proteins, like lysine, might enhance magnesium absorption more effectively than plant proteins.
  2. Excessive protein may lead to increased urinary excretion of magnesium.
  3. Insufficient protein may impair the formation of transport proteins that aid in magnesium absorption.

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Food Sources

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.

Sample Foods High in: Protein
View Additional Food Sources
Food Description Nutrient Amount1 Daily Value%2
Beef, round, bottom round, steak, separable lean and fat, trimmed to 1/8" fat, all grades, cooked, braised
Category: Beef Products
32.76 g 65.52%
Pork, fresh, loin, tenderloin, separable lean only, cooked, broiled
Category: Pork Products
30.42 g 60.84%
Chicken, broiler or fryers, breast, skinless, boneless, meat only, cooked, braised
Category: Poultry Products
32.1 g 64.20%
Fish, tuna, fresh, bluefin, cooked, dry heat
Category: Finfish and Shellfish Products
29.91 g 59.82%
Cheese, parmesan, low sodium
Category: Dairy and Egg Products
41.6 g 83.20%
Egg, whole, cooked, fried
Category: Dairy and Egg Products
13.61 g 27.22%
Soybeans, mature cooked, boiled, without salt
Category: Legumes and Legume Products
18.21 g 36.42%
Peanuts, all types, oil-roasted, without salt
Category: Legumes and Legume Products
28.03 g 56.06%
Oats (Includes foods for USDA's Food Distribution Program)
Category: Cereal Grains and Pasta
16.89 g 33.78%
1 Nutrient amount is in 100 gram food
2 Use FDA 2000 calorie diet as Daily Value reference

Additional Nutrient Information
Nutrient Summary 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.
Deficiency Health Effects 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
Effects if Above Upper Limit 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.

External References
Additional Information 9 Essential Amino Acids:

Daily Value Age Group Recommended Daily Values
Toddler 1 to 3 years old: 13 g
Child 4 to 8 years old: 19 g
Male 9 to 13 years old: 34 g
Male 14 to 18 years old: 52 g
Male 19 to 30 years old: 56 g
Male 31 to 50 years old: 56 g
Male 51 to 70 years old: 56 g
Male Senior 71 or older: 56 g
Female 9 to 13 years old: 34 g
Female 14 to 18 years old: 46 g
Female 19 to 30 years old: 46 g
Female 31 to 50 years old: 46 g
Female 51 to 70 years old: 46 g
Female Senior 71 or older: 46 g
Female Pregnancy (>18): 71 g
Female Lactation (>18): 71 g
FDA (Based on 2000 calorie daily diet): 50 g

Dietary Reference Intakes The nutrient Dietary Reference Intakes and nutrition facts is from Institute of Medicine of National Academies 2006. Dietary Reference Intakes: The Essential Guide to Nutrient Requirements. Washington, DC: The National Academies Press.
US FDA Nutrition Education Nutrition facts knowledge are based on U.S. FOOD & DRUG Administration Nutrition Education Resources & Materials.
National Institutes of Health Nutrition facts knowledge are based on National Institutes of Health Dietary Supplement Fact Sheets.
Disclaimer The nutrient information provided here should not take the place of medical advice. We encourage you to talk to your healthcare providers (such as your doctor) about your dietary requirements which are best for your overall health. We also recommend you to read organization or professional reference documents or articles mentioned, but not limited to, in this page. Any mentions and reference links in this page don't represent our endorsement of their services and advice.

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