72 Unit 2 Nutrition and Food Choices
Copyright Goodheart-Willcox Co., Inc.
You need to take in protein to replace what is lost every day. Fortu-
nately, in the United States, many foods that people eat on a regular basis
contain protein. If you’re like most Americans, you eat more protein than
you need.
Types of Proteins
All proteins are made up of smaller chemical units called amino acids
(Figure 3.3). Twenty different amino acids join in various combinations to
make all types of protein. Some of these amino acids are produced in the
body. These are called nonessential amino acids.
Other types of amino acids are not produced by the body; you can only
get them by eating particular foods. This type of amino acid is called an
essential amino acid because it is essential that your diet includes this type
of nutrient.
Protein sources are divided into two types, depending on whether or
not they include all of the essential amino acids:
• A complete protein source contains all nine of the essential amino
acids. This type of protein is found in animal-based foods such as
meat, poultry, eggs, fi sh, and dairy products (milk and cheese).
• An incomplete protein source lacks one or more of the essential
amino acids. This type of protein is found in legumes (dry beans
and peas), tofu, nuts and seeds, grains, some vegetables, and some
fruits.
Protein’s Role in the Body
Protein is required for the body to function properly. People who
don’t consume enough protein risk serious consequences. For ex-
ample, since immune cells are made of protein, individuals who
have a protein defi ciency are more likely to have weakened im-
mune systems, which make it more likely for them to develop
infections and diseases.
Protein plays other important roles in the body, includ-
ing acting as enzymes and hormones. Hormones are chemi-
cal messengers that infl uence many basic processes in your
body. Protein also serves as a transporter in the body and is
involved in fl uid and pH balance.
Protein and Vegetarians
Because some vegetarians avoid eating all (or most) foods from ani-
mal sources, they must rely on plant-based sources of protein to meet their
protein needs. With some planning, a vegetarian diet can easily meet the
recommended protein needs of adults and children. People who eat a veg-
etarian diet need to take in different types of food that can work together
to provide all of the essential amino acids.
amino acid
a small chemical unit that
makes up proteins
hormone
a chemical substance in
your body that infl uences
many basic processes
Steak is a complete protein,
meaning it contains all nine
essential amino acids. Do
you consider complete
protein foods like steak to
be “healthy”? Why or why
not?
Figure 3.3