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Chapter 5

Protein

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Learning Objectives

1. Identify and describe the building blocks of protein

2. List the functions of protein in the body

3. Explain how protein is digested, absorbed, and metabolized

4. Distinguish between complete protein and incomplete protein and list examples of foods that contain each

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Learning Objectives (cont’d)

5. Explain the potential consequences of eating too much or too little protein

6. State the dietary recommendations for protein

7. Discuss the nutrition and uses of meat, poultry, and fish on the menu

8. Describe soy products, their health benefits, and how to use them on the menu

9. Discuss the advantages and disadvantages of irradiation

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Protein

Essential part of all living cells found in animals and plants

Protein is in your skin, hair, nails, muscles, etc

Made of amino acids – amino acids contain nitrogen, which is necessary for life

Particularly rich in animal foods – meats, poultry, eggs, etc

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Structure of Protein

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Part of a Protein

Proteins often contain 35 to several hundred or more amino acids

Amino Acid Amino Acid Amino Acid

Peptide bonds – the bonds that form between adjoining amino acids.

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Essential & Nonessential Amino Acids

Essential or indispensable amino acids

Nonessential amino acids One of more may become essential –

conditionally essential

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Proteins

Protein fragments with 10 or more amino acids are called:

Polypeptides

Each of the over 50,000 different proteins in the body contains its own unique number and sequence of amino acids

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Functions of Protein

Acts as a structural

component of the body Builds and maintains

the body tissues

Found in many enzymes and hormones, and all antibodies

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How Enzymes Work

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Functions of Protein (cont’d)

Act as taxicabs transporting iron and other minerals, fats, and oxygen

Maintains fluid and acid-base balance of the blood

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Functions of Protein (cont’d)

Helps blood clot

Last resort: provide energy

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Nutrition Science Focus: Proteins

Primary structure of protein: the number of sequence of the amino acids

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Nutrition Science Focus: DNA

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Digestion, Absorption, and Metabolism

Stomach Hydrochloric acid

denatures protein enough so enzymes can enter and do their work

Hydrochloric acid also activates pepsinogen to pepsin – an enzyme that splits peptide bonds

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Digestion, Absorption, and Metabolism

Small intestine Proteases split up proteins into short, peptide chains

and amino acids Brush border of small intestine makes several

peptidases – enzymes that break down short peptide chains into amino acids, dipeptides, and tripeptides

As dipeptides and tripeptides enter the intestinal cells, they are split into amino acids

Amino acids travel in blood to liver and body cells Amino acid pool provides cells with a supply of amino

acids.

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Protein in Food

Animal foods (complete proteins)

Plant foods (incomplete proteins)

Spaghetti with Meatballs

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One ounce of meat, poultry, or fish =

Protein found in:

- 1 egg

- ¼ cup cooked dry beans or tofu

- 1 tablespoon peanut butter

- ½ ounce nuts or seeds

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Complementary Proteins

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Protein and Health

Eating too much protein has no benefits and may result in: Excessive kcalories Excessive fat if you are eating too much high-

fat animal foods Calcium loss

High intakes of animal proteins are associated with certain cancers, such as cancer of the colon

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Protein and Health

Eating too little protein can: Slow down the protein rebuilding and repairing

process Weaken the immune system

Eating too little protein in many developing countries leads to PEM Kwashiorkor Marasmus

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Dietary Recommendations for Protein

RDA: 0.8 g/kg or 0.36 g/lb body weight Nitrogen balance

Positive N balance Negative N balance

AMDR for protein Children from 1 to 3 years old: 5 to 20% Children from 4 to 18 years old: 10 to 30% Adults: 10 to

35%

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Ingredient Focus: Meat, Poultry, & Fish

Most fish is lower in fat, saturated fat, and cholesterol than are meat and poultry

When choosing beef, you will get the least fat from eye of round, followed by top round and bottom round

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Chicken and Turkey

Chicken is twice as fatty as turkey. The skin of chicken and turkey contains much of the bird’s fat

White meat chicken and turkey have less fat than dark meat

Ground turkey or chicken have varying amounts of fat

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Ingredient Focus: Meat, Poultry, & Fish

Meat is a good source of protein, iron, copper, zinc, and some of the B vitamins

Chicken and turkey are rich in protein, niacin, and vitamin B6. Also good sources of riboflavin, vitamin B12, iron, zinc, and magnesium

Fish are excellent sources of protein, low in kcalories, and good sources of certain vitamins and minerals

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Steps to Prepare Healthy Meat, Poultry, & Fish Select a lean cut Use flavorful rubs and marinades Choose a cooking method that will provide a

flavorful, moist product and that adds little or no fat to the food

Think of how to flavor the dish (i.e. herbs and spices, smoking, etc.)

Fish must be cooked very carefully and not overdone. Serve immediately

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Culinary Science: Denaturation

A process in which a protein uncoils and loses its shape

Denaturation causes the protein to lose its ability to function

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Food Facts: Soybeans

Tofu Soy sauce Miso Tempeh Textured vegetable

protein – TVP Meat analogs

Tofu Lasagna

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Health Benefits of Soybeans

If you consume 25 grams of soy protein/day, as part of a diet low in saturated fat and cholesterol, you may reduce your risk of heart disease by reducing blood cholesterol levels

Soy may help women promote bone health after menopause – soy’s possible role in breast cancer risk is uncertain

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Hot Topic: Irradiation

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