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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
6.
7.
8.
9.
eating too much or too little protein
State the dietary recommendations for
protein
Discuss the nutrition and uses of meat,
poultry, and fish on the menu
Describe soy products, their health benefits,
and how to use them on the menu
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 highfat 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
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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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