730
UNIT FIVE
d. Vitamin E
(1) Vitamin E is an antioxidant.
(2) It is stored in muscles and adipose tissue.
(3) It prevents breakdown of polyunsaturated fatty
acids and stabilizes cell membranes.
e. Vitamin K
(1) Vitamin K is in foods and is produced by
intestinal bacteria.
(2) Some vitamin K is stored in the liver.
(3) It is used to produce prothrombin, required for
blood clotting.
2. Water-soluble vitamins
a. General characteristics
(1) Water-soluble vitamins include the B vitamins
and vitamin C.
(2) Cooking or processing food destroys some
water-soluble vitamins.
(3) B vitamins make up a group called the vitamin
B complex and oxidize carbohydrates, lipids,
and proteins.
b. Vitamin B complex
(1) Thiamine (vitamin B
1
)
(a) Thiamine functions as part of coenzymes
that oxidize carbohydrates and synthesize
essential sugars.
(b) Small amounts are stored in the tissues;
excess is excreted in the urine.
(c) Quantities needed vary with caloric intake.
(2) Ribofl
avin (vitamin B
2
)
(a) Ribofl
avin functions as part of several
enzymes and coenzymes essential to the
oxidation of glucose and fatty acids.
(b) Its absorption is regulated by an active
transport system; excess is excreted in the
urine.
(c) Quantities required vary with caloric intake.
(3) Niacin (nicotinic acid or vitamin B
3
)
(a) Niacin functions as part of coenzymes
required for the oxidation of glucose and
for the synthesis of proteins and fats.
(b) It can be synthesized from tryptophan;
daily requirement varies with the
tryptophan intake.
(4) Pantothenic acid (vitamin B
5
)
(a) Pantothenic acid functions as part of
coenzyme A; thus, it is essential for
energy-releasing mechanisms.
(b) Most diets provide sufF
cient amounts;
deF
ciencies are rare.
(5) Vitamin B
6
(a) Vitamin B
6
is a group of compounds
that function as coenzymes in metabolic
pathways that synthesize proteins, certain
amino acids, antibodies, and nucleic acids.
(b) Its requirement varies with protein intake.
(6) Cyanocobalamin (vitamin B
12
)
(a) The cyanocobalamin molecule contains
cobalt.
(b) Its absorption is regulated by the secretion
of intrinsic factor from the gastric glands.
(c) It functions as part of coenzymes needed
for nucleic acid synthesis and for the
metabolism of carbohydrates and fats.
18.5
ENERGY EXPENDITURES (PAGE 706)
Energy is of prime importance to survival and may be
obtained from carbohydrates, fats, or proteins.
1. Energy values of foods
a. The potential energy values of foods are expressed
in calories.
b. When energy losses due to incomplete absorption
and incomplete oxidation are taken into account,
1 gram of carbohydrate or 1 gram of protein yields
about 4 calories, whereas 1 gram of fat yields
about 9 calories.
2. Energy requirements
a. The amount of energy required varies from person
to person.
b. ±actors that infl
uence energy requirements include
basal metabolic rate, muscular activity, body
temperature, and nitrogen balance.
3. Energy balance
a. Energy balance exists when caloric intake equals
caloric output.
b. If energy balance is positive, body weight increases;
if energy balance is negative, body weight decreases.
4. Desirable weight
a. The most common nutritional disorders involve
caloric imbalances.
b. Average weights of persons 25–30 years of age are
desirable for older persons as well.
c. Body mass index assesses weight taking height
into account.
d. A BMI between 25 and 30 indicates overweight,
and above 30, obesity.
18.6
VITAMINS (PAGE 709)
Vitamins are organic compounds (other than
carbohydrates, lipids, and proteins), that cannot be
synthesized by body cells in adequate amounts and are
essential for normal metabolic processes.
1. ±at-soluble vitamins
a. General characteristics
(1) ±at-soluble vitamins are carried in lipids and
are infl
uenced by the same factors that affect
lipid absorption.
(2) They resist the effects of heat; thus, they are
not destroyed by cooking or food processing.
b. Vitamin A
(1) Vitamin A exists in several forms, is
synthesized from carotenes, and is stored in
the liver.
(2) It is an antioxidant required for production of
visual pigments.
c. Vitamin D
(1) Vitamin D is a group of related steroids.
(2) It is found in certain foods and is produced
commercially; it can also be synthesized in the
skin.
(3) When needed, vitamin D is converted by
the kidneys to an active form that functions
as a hormone and promotes the intestine’s
absorption of calcium and phosphorus.
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