chapter 5 Thermodynamics, Chemical Kinetics, and Energy Metabolism
endocrine disorders, behavior, lifestyle and physical ac-
tivity, eating habits, and culture. Obesity is the most
common nutritional disorder in developed countries.
A sedentary lifestyle is a significant contributing fac-
tor in insidious weight gain. Sedentary lifestyles may
not only predispose individuals to obesity but also lead
to degenerative arterial diseases. A sound exercise pro-
gram coupled with good nutrition can help maintain health
and quality of life. Obese individuals who wish to lose
weight by dietary restriction and increased physical ac-
tivity should be under medical supervision. The human
body needs a wide variety of nutrients to function op-
Recommended Dietary Allowance
), pub-
lished by the Food and Nutrition Board of the National
Academy of Sciences National Research Council (USA),
provides a broad guideline of the amounts of some of
the well-established nutrients (protein, vitamins, and min-
erals) that should be consumed
to maintain nor-
mal health (RDA values are given in Appendix IV).
To use the RDA properly, keep in mind the following:
1. RDA values are overestimates of nutrient
requirements; minimum quantities of nutrients
required to maintain normal function and health in
humans are either unknown or incompletely known.
2. RDA values relate primarily to populations of
developed countries and are intended to meet the
needs of virtually all healthy individuals. Thus, the
allowances are far higher than demanded by
physiological needs, and for many populations of the
world, the RDA estimates may be inappropriately
high. If the intake of a given nutrient is below the
RDA value, nutritional inadequacy does not
necessarily result. However, if a particular deficiency
is accompanied by biochemical and clinical
abnormalities, then corrective action is needed.
T A B L E 5-5
Food Groups
Clinical conditions include trauma and stress,
prematurity, inherited metabolic disorders, disease
states and rehabilitation, and use of certain drugs.
3. Since the RDA applies to healthy people, it does not
provide requirements in disease states or in
drug-nutrient interactions.
4. RDA does not address the fact that some nutrients
possess pharmacological activities unrelated to
nutrient function. Excessive intake of such nutrients
can have toxic effects.
5. RDA does not provide values for all essential
nutrients, and therefore the daily requirement
should be met by selection from a wide variety of
foods. No single food source is nutritionally
complete. Foods are categorized into four
) milk and milk products,
) meat and meat
alternatives (e.g., legumes, nuts, and milk products),
3) fruits and vegetables, and 4) breads and cereals.
Table 5-5 lists the key nutrients in some representative
foods in each group. Not only is consumption of
adequate amounts of nutrients essential but so is
consumption of appropriate quantities of foods that
provide amounts of energy commensurate with
physical activity and the physiological state.
Knowledge of a given nutrient
known as nutrient
) per unit of energy (e.g.,
1 0 0 0
kcal) in a specific food is useful in adjusting the
diet to individual need. Dietary fiber, although not
nutritionally essential, is important in maintaining
good health. Dietary fiber consists of polymers of
sugars and other indigestible substances. Fiber affects
nutrient absorption and makes the contents of the gut
bulky and soft. In terms of the four food groups
(Table 5-4), fiber can be obtained from the second
group by selection of dry beans, peas, and nuts in
place of (or in addition to) meat, poultry, and fish
M ajor Nutrients Provided
1. Milk and milk products (e.g., milk, yogurt, cheese, ice cream)
2. Meat (e.g., beef, pork, poultry, fish) and meat alternatives
(e.g., legumes, nuts, milk products)
3. Fruits and vegetables (e.g., green leafy, deep yellow, or orange
vegetables, citrus fruits)
4. Breads, cereals, and grains
Calcium, riboflavin, protein
Protein, niacin, iron,
thiamine (vitamin Bi),
Vitamins A and C
Carbohydrate, thiamine, iron, niacin
*A well-balanced diet includes a variety of foods on a daily basis, selected from each of the four food groups. With proper planning a vegetarian diet
can be nutritionally adequate. Special foods consumed by ethnic groups should be considered in diet planning. Basic principles of a good diet in-
clude consumption of a variety of foods; consumption to maintain ideal body weight; moderation in intake of foods or beverages rich in saturated
fats, cholesterol, sugar, and sodium salts; and consumption of adequate quantities of fruits, vegetables, and whole grains.
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