Your Diet Contains Many Nutrients
and identify the six
main types of nutrients.
the guidelines for healthy eating.
minerals in your diet and their
the principal vitamins and explain their
ou have learned that the purpose of the diges-
tive system is to break down food and absorb
nutrients. But what are nutrients? Nutrients
are chemical substances in food that the cells
of your body need for growth, maintenance, and repair.
Nutrients include carbohydrates, lipids, proteins, water,
minerals, and vitamins. Essential nutrients are specific
substances that your body cannot make on its own in suf-
ficient quantities to meet its needs. Essential nutrients in-
clude some amino acids, fatty acids, vitamins, and minerals.
When planning your diet, there are two things to
your food contains. Do
not confuse a Calorie (with a capital C) with
a calorie (cal), the amount of heat needed
to raise the temperature of 1
g of water
from 14°C to 15°C; 1
Calorie equals 1,000
The distribution of the food types in the
diet (such as, carbohydrates, fats, and proteins). Diets
vary worldwide with food availability and cultures.
Most experts recommend a diet with the following
distribution of calories: 50-60% carbohydrates, 30%
fats, and 12-15% proteins.
Suggestions for healthy eating include the following:
Eat a variety of foods.
Maintain a healthy weight.
minerals are found in your bones and teeth. Minerals have
important functions in the structure of bone, regulation
of enzymatic functions, maintenance of pH of body flu-
ids, osmosis, and generation of action potentials in nerves
and muscles. For example, the mineral magnesium is an
important cofactor for enzymes that convert ADP to ATP
(see Chapter 2). Minerals that are vital to the body include
calcium, phosphorus, potassium, sulfur, sodium, chloride,
Vitamins are organic nutrients that are required
in small amounts to maintain normal growth and me-
tabolism. Most vitamins
(molecules that help enzymes do their jobs)
in chemical reactions. They are classified as
either fat-soluble vitamins
vitamins A, D, E, and K) or water-soluble
vitamins (for example,
vitamins B and C).
Fat-soluble vitamins are absorbed from the di-
gestive tract and transported in chylomicrons.
In contrast, water-soluble vitamins are dis-
solved in body fluids. While excess quantities of fat-sol-
uble vitamins can be stored in cells, excess quantities of
water-soluble vitamins cannot and are instead excreted
in the urine.
Two vitamins (C, E) and a
damaging free radicals of oxygen.
These vitamins are also called an-
An expression of the
amount of energy in
various foods and
a measurement of
metabolic rate that
is equal to 1,000
chemical precursor to
Choose foods low in fat, saturated fat, and cholesterol.
Eat plenty of vegetables, fruits, and grain products.
Use sugars in moderation only.
In 2005, the U.S. Department of Agriculture (USDA) ad-
opted a new, personalized approach to nutritional guide-
M y P y ra m id
Your diet should include minerals, inorganic ele-
ments that constitute about 4% of your body weight. Most
is an essential nutrient?
are the recommendations for calorie distri-
bution for protein, fat, and carbohydrate intake?
is calcium important for your body?
is the function of vitamin D?
416 CHAPTER 14
The Digestive System, Nutrition, and Metabolism