80

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-

timally.

Recommended Dietary Allowance

(

RDA

), 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

daily

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

groups:

1

) milk and milk products,

2

) 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

concentration

(also

known as nutrient

density

) 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

Group

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.