Biology of Disease

10.2 Diet and Nutrition

Food is obviously needed to sustain life but a balanced diet is vital for good

health. General evidence for good nutrition is a well developed body with an

ideal weight (Section 10.3), good skin, including hair, and muscle tone, and

physical and mental alertness. The food eaten by an individual constitutes the

diet and it should supply appropriate amounts and proportions of a variety

of substances, usually called nutrients. Some nutrients, the macronutrients,

such as carbohydrates, lipids and proteins, are required in amounts that are

large compared with the micronutrients, such as vitamins, minerals and

trace elements, which are needed in much smaller quantities. Nutrients

are needed to sustain a number of activities within the body if good health

is to be maintained. They supply the raw materials required for growth and

maintenance of tissues, include substances that help regulate metabolism,

for example the cofactors and coenzymes necessary for enzyme activities

and provide the energy to drive metabolism and maintain homeothermy.

Nutrients vary in their contributions to these roles and there is also overlap

between their contributions to each (Figure 10.1).

Nutrients and Energy

Diets are often described in terms of their energy content, despite the fact

that they need to supply materials for needs other than just their energy

provision (Figure 10.1). It is possible for a diet to supply an adequate amount

of energy but be deficient in some essential raw materials, such as vitamins

and minerals needed by the individual. A balanced diet is one that supplies

adequate energy distributed appropriately between carbohydrates, lipids,

and proteins and contains the necessary amounts of vitamins, minerals, trace

elements, water and nondigestible fiber.

Nutritional energy is usually measured in joules or kilojoules. The number of

joules required by any one person needs to be matched to their energy output

(Table 10.1). The term recommended daily amount (RDA) was originally used

by the UK Department of Health in 1979 to define the amounts of certain

nutrients needed by different groups within the population.

X]VeiZg&%/ DIET AND DISEASE

')% W^dad\nd[Y^hZVhZ

Carbohydrates

Lipids (fat)

Proteins

Vitamins

Minerals

Trace elements

Necessary

for growth

and tissue

repair

Oxidized for

energy

Contribute to

the regulation

of metabolism

Nutrients

Figure 10.1 Overview of the general roles of

nutrients.

Group Approximate daily energy requirements

/kJ required per kg desirable body weight

Babies up to one year old 500

Children one to 10 years old 335–420

Male children 11–15 years old 270

Female children 11–15 years old 145

Sedentary males and most females 117

Physically active males and females 125

Males and females over 55 years old 117

Pregnant females (first trimester) 117–134

Pregnant females (second and third trimesters) 150–159

Lactating females 150–159

Table 10.1Energy required to maintain body functions. For example, a physically active man

weighing 70 kg requires 70q125 = 875 kJ (or 2080 kcalories) daily.