Your Diet Contains Many Nutrients
LEARNING OBJECTIVES
1.
Define
the term
nutrient
and identify the six
main types of nutrients.
2.
Outline
the guidelines for healthy eating.
3.
Identify
minerals in your diet and their
importance.
4.
List
the principal vitamins and explain their
functions.
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
consider:
How many
C alories
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
calories.
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,
and magnesium.
Vitamins are organic nutrients that are required
in small amounts to maintain normal growth and me-
tabolism. Most vitamins
serve
as
coenzym es
(molecules that help enzymes do their jobs)
in chemical reactions. They are classified as
either fat-soluble vitamins
(for
example,
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
pro-
vitam in
(beta-carotene) inactivate
damaging free radicals of oxygen.
These vitamins are also called an-
tioxidant vitamins.
Calorie
(KAL-o-re)
An expression of the
amount of energy in
various foods and
a measurement of
metabolic rate that
is equal to 1,000
calories.
pro-vitam in
A
chemical precursor to
a vitamin.
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-
lines called
M y P y ra m id
(Figure 14.10).
Your diet should include minerals, inorganic ele-
ments that constitute about 4% of your body weight. Most
CONCEPT CHECK
1.
What
is an essential nutrient?
2.
What
are the recommendations for calorie distri-
bution for protein, fat, and carbohydrate intake?
3.
Why
is calcium important for your body?
4.
What
is the function of vitamin D?
416 CHAPTER 14
The Digestive System, Nutrition, and Metabolism
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