Carbohydrates Are a Primary Fuel Source
Carbohydrates are the primary source of fuel for our bodies,
particularly for our brain and during physical exercise ( Figure 1.5 ). A close look at the word
“carbohydrate” reveals the chemical structure of this nutrient. Carbo - refers to carbon, and - hydrate
refers to water. You may remember that water is made up of hydrogen and oxygen. Thus, carbohydrates
are composed of chains of carbon, hydrogen, and oxygen.
As we read before, carbohydrates provide 4 calories per gram.
Carbohydrates encompass a wide variety of foods; rice, wheat, and other grains, as well as vegetables
are carbohydrates, and fruits contain natural sugars that are carbohydrates. Carbohydrates are also
found in legumes (including lentils, dry beans, and peas), milk and other dairy products, seeds, and nuts.
Carbohydrates and their role in health are the subject of Module 4 .
Fats Provide Energy and Other Essential Nutrients
Fats , a type of lipids, are another important source of
energy for our bodies ( Figure 1.6 ). Lipids are a diverse group of organic substances that are insoluble in
water. Lipids include triglycerides (more commonly known as fats), phospholipids, and sterols. Like
carbohydrates, fats are comprised of carbon, hydrogen, and oxygen; however, they contain proportionally
much less oxygen and water than carbohydrates do. This quality allows them to pack together tightly,
which explains why they yield more energy per gram than either carbohydrates or proteins.
Fat is an important energy source for our bodies at rest and during low intensity exercise. Our body is
capable of storing large amounts of fat as adipose tissue. These fat stores can be broken down for energy
during periods of fasting, for example, while we are asleep. Foods that contain fats are also important in
providing fat-soluble vitamins and essential fatty acids.
Dietary fats come in a variety of forms. Solid fats
include such things as butter, lard, and margarine. Liquid fats are referred to as oils and include vegetable
oils such as canola and olive oils. Cholesterol is a form of lipid that is synthesized in our bodies, and it can
also be consumed in the diet. Module 5 provides a thorough review of lipids.
Proteins Support Tissue Growth, Repair, and Maintenance
Like carbohydrates and fats, proteins also
contain carbon, hydrogen, and oxygen, but they are different from carbohydrates and fats in that they
contain the element nitrogen. Within proteins, these four elements assemble into small building blocks
known as amino acids. We break down dietary proteins into amino acids and reassemble them to build
our own body proteins—for instance, the proteins in our muscles and blood.
Although proteins can provide energy, they are not a primary source of energy for our bodies. Proteins