http://www.ck12.org Chapter 1. Human Biology
FIGURE 1.24
Up to the age of 13 years, you need about
130 grams of carbohydrates a day. Most
of the carbohydrates should be complex.
They are broken down by the body more
slowly than simple carbohydrates. There-
fore, they provide energy longer and more
steadily.Complex Carbohydrates
Starchis a large, complex carbohydrate. Starches are found in foods such as vegetables and grains. Starches are
broken down by the body into sugars that provide energy.
Fiberis another type of large, complex carbohydrate that is partly indigestible. Unlike sugars and starches, fiber does
not provide energy. However, it has other important roles in the body. For example, fiber is important for maintaining
the health of your gastrointestinal tract. Eating foods high in fiber also helps fill you up without providing too many
calories. Most fruits and vegetables are high in fiber. Some examples are pictured below (Figure1.25).
Proteins
Proteinsare nutrients made up of smaller molecules calledamino acids. The amino acids are arranged like "beads
on a string." These amino acid chains then fold up into a three-dimensional molecule, giving the protein a specific
function. Proteins have several important roles in the body. For example, proteins make up muscles and help control
body processes.
If you eat more than you need for these purposes, the extra protein is used for energy. The image below shows how
many grams of protein you need each day (Figure1.26). It also shows some foods that are good sources of protein.
Lipids
Lipidsare nutrients, such as fats that store energy. Lipids also have several other roles in the body. For example,
lipids protect nerves and make up the membranes that surround cells.