70 Unit 2 Nutrition and Food Choices
Copyright Goodheart-Willcox Co., Inc.
Carbohydrates
Carbohydrates, a major source of energy for the body, are found in fruits,
vegetables, grains, and milk products. Carbohydrates are also known as
saccharides, or sugar and starch molecules. These molecules serve as a source
of chemical energy that the body can utilize quickly. Carbohydrates can
be described as either simple or complex. There are three distinct types of
carbohydrates: sugar, starch, and fi ber.
Sugars
Sugars such as fructose, glucose, sucrose, and lactose, are classifi ed
as simple carbohydrates. These simple sugar compounds occur naturally in
some foods, including fruits, maple syrup, and dairy products.
Glucose is the preferred source of energy for your brain and central
nervous system. It is glucose that powers your brain, enabling you to con-
centrate and pay attention in class.
The table sugar people add to their coffee or use in baking is sucrose,
which has been extracted from sugarcane or sugar beets. When sugar ap-
pears in the ingredient list of a processed food, the product contains su-
crose. It is common for processed foods such as cereals, breads, desserts,
and sugar-sweetened beverages to contain added sugars such as sucrose.
Starches
Starches, which are chains of glucose linked together, are called com-
plex carbohydrates. During digestion, your body breaks down starches into
smaller glucose units, making the glucose available for use as energy. Prod-
ucts made from grains, such as bread, cereal, rice, and pasta, are rich sourc-
es of starch. Starch is also found in beans and in some types of vegetables,
including potatoes, peas, and corn.
Supplying Energy
Your body breaks down carbohydrates into glucose to obtain energy.
Have you ever skipped breakfast and then had trouble concentrating in
one of your early morning classes? This diffi culty is caused by your body
running out of glucose.
When it is in need of energy, the body can use glucose immediately. This
is why having a candy bar or soft drink, both loaded with sugar, can give
you a quick “pick-me-up.” The sucrose in these snacks is quickly and easily
broken down into glucose and fructose. Later in this chapter, you will learn
about the disadvantages of relying on these types of foods for energy.
Glucose can also be stored in the liver and muscles for later use. When
glucose is stored in these areas, it is known as glycogen. However, after
enough glycogen has been stored, any extra glucose is converted by the
liver into fat, which is stored in the fat tissue. The body uses glycogen from
the muscles and liver, or the fat stored in the fat tissue, when it needs en-
ergy between meals or to fuel activity.
carbohydrate
a nutrient and major
source of energy for the
body
glucose
a type of carbohydrate
and the preferred source of
energy for the brain and
central nervous system
glycogen
a stored version of glucose
located in the muscles
and liver; supplies energy
between meals