You need to know nutritional requirements of an individual or group for two major reasons:

Prescriptive reasons: that is, to provide or dispense food supplies; for example:

• to procure food for national consumption
• to secure food for institutional consumption
• to run nutritional supplementation programmes.

Diagnostic reasons: mainly to identify whether a group or an individual is suffering from malnutrition of any kind; for example:

• to evaluate nutritional intervention programmes
• to determine whether the food available in the stock is adequate to feed the household or nation for a certain duration of time.

In order to estimate nutritional requirements of individuals or groups, we need to consider the following factors:

• Physical activity — whether a person is engaged in heavy physical activity
• The age and sex of the individual or group
• Body size and composition — what the general build is of a person or group
• Climate — whether a person or group is living in hot or cold climate
• Physiological states, such as pregnancy and lactation.

Based on these factors, nutritional requirements in the different segments of the population can be classified into four groups. These correspond to different parts of the lifespan, namely (a) pregnancy and lactation, (b) infancy and childhood (c) adolescence and adulthood, and (d) old age. You are now going to look at each of these in turn.