723
CHAPTER EIGHTEEN
Nutrition and Metabolism
cusses some ways that understanding nutrition can help
athletic performance.
PRACTICE
75
What is an adequate diet?
76
What factors inF
uence individual needs for nutrients?
77
Describe ways that consumers can make wise food choices.
Malnutrition
Malnutrition
(mal
nu-trish
un) is poor nutrition that results
from a lack of essential nutrients or a failure to utilize them.
It may result from
undernutrition
and produce the symptoms
of deF
ciency diseases, or it may be due to
overnutrition
aris-
ing from excess nutrient intake.
A variety of factors can lead to malnutrition. ±or example, a
deF ciency condition may stem from lack of availability or poor
quality of food. On the other hand, malnutrition may result
from overeating or taking too many vitamin supplements.
Malnutrition from diet alone is called
primary malnutrition.
Secondary malnutrition
occurs when an individual’s
characteristics make a normally adequate diet insufF cient.
weight loss goals. Past pyramids can seem strange in light
of today’s individualized goals, depicted in
f
gure 18.20
. A
plan from the 1940s had eight categories, including sepa-
rate groups for butter and margarine, and for eggs—foods
now associated with the development of heart disease. In
the 1920s, an entire food group was devoted to sweets!
Although many types of diets work well for many people, a
good general approach is to emphasize fresh fruits and veg-
etables and whole grains and to minimize processed foods,
which are often high in fat and/or sugar.
When making individual food choices, it helps to read
and understand food labels. Disregard claims such as
“light” and “low fat” and skip right to the calories or grams
of different ingredients. “Light” can mean many things: that
the nutritionally altered form contains one-third fewer calo-
ries or half the fat of the reference food, that the sodium
content has been reduced by 50%, or it may describe the
texture and color of the food. “Low fat” indicates 3 grams
of fat or less per serving. Many times when fat is removed,
sugar is added, so the calories of a low-fat product may be
more, not less—just compare the ingredients lists on vari-
ous ice cream cartons to see this. Ingredients are listed in
descending order by weight. Clinical Application 18.3 dis-
TABLE
18.11
|
Trace Elements
Trace
Element
Distribution
Functions
Sources and RDA*
for Adults
Conditions Associated with
Excesses
De±
ciencies
Iron
(±e)
Primarily in blood;
stored in liver, spleen,
and bone marrow
Part of hemoglobin molecule; catalyzes
formation of vitamin A; incorporated into a
number of enzymes
Liver, lean meats, dried apricots,
raisins, enriched whole-grain
cereals, legumes, molasses
10–18 mg
Liver damage
Anemia
Manganese
(Mn)
Most concentrated
in liver, kidneys, and
pancreas
Activates enzymes required for fatty acids and
cholesterol synthesis, formation of urea, and
normal functioning of the nervous system
Nuts, legumes, whole-grain cereals,
leafy green vegetables, fruits
2.5–5 mg
None known
None known
Copper
(Cu)
Most highly
concentrated in liver,
heart, and brain
Essential for hemoglobin synthesis, bone
development, melanin production, and myelin
formation
Liver, oysters, crabmeat, nuts,
whole-grain cereals, legumes
2–3 mg
Rare
Rare
Iodine
(I)
Concentrated in
thyroid gland
Essential component for synthesis of thyroid
hormones
±ood content varies with soil
content in di²
erent geographic
regions; iodized table salt
0.15 mg
Decreased
uptake by the
thyroid gland
Decreased
synthesis
of thyroid
hormones
Cobalt
(Co)
Widely distributed
Component of cyanocobalamin; required for
synthesis of several enzymes
Liver, lean meats, milk
No RDA established
Heart disease
Pernicious
anemia
Zinc
(Zn)
Most concentrated
in liver, kidneys, and
brain
Component of enzymes involved in digestion,
respiration, bone metabolism, liver metabolism;
necessary for normal wound healing and
maintaining integrity of the skin
Meats, cereals, legumes, nuts,
vegetables
15 mg
Slurred
speech,
problems
walking
Depressed
immunity, loss
of taste and
smell, learning
di³
culties
Fluorine
(±)
Primarily in bones and
teeth
Component of tooth structure
±luoridated water
1.5–4 mg
Mottled teeth
None known
Selenium
(Se)
Concentrated in liver
and kidneys
Components of certain enzymes
Lean meats, ´
sh, cereals
0.05–2 mg
Vomiting,
fatigue
None known
Chromium
(Cr)
Widely distributed
Essential for use of carbohydrates
Liver, lean meats, wine
0.05–2 mg
None known
None known
RDA = recommended daily allowance.
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