Chapter 2


1.2 Definitions

Nutrients constitute the active elements of foods which are utilised in the functioning of the
body. They comprise proteins, fats, carbohydrates, vitamins, minerals and trace elements, as
well as water. Foods contain some or all of these nutrients in variable proportions.

Foods are traditionally categorised in eight groups:

- cereals (millet, sorghum, maize, wheat...)
- roots and tubers (manioc, yams, sweet potato, Irish potato..)
- sugar and honey
- fats ( butter, oil..)
- fruits and vegetables
- meat, offal, eggs and fish
 milk and milk products
- legumes (nuts, lentils, beans...)

The expression nutritional requirements refers to the quantity of energy and of nutrients,
expressed on a daily basis, necessary for a given category of individuals that will allow these
individuals, when in good health, to develop and lead a normal life.

Nutritional requirements have been established on the basis of physiological studies
(metabolic balances) and field epidemiological studies. Requirements vary according to age,
sex, body weight, level of activity and physiological status (for example, pregnancy and
lactation). They are expressed in the form of averages, taking into account individual
variation.

Reference nutrient intakes (RNIs) are used as a standard to assess the adequacy of intake of
various nutrients. They are evaluated by national or international committees of experts, on
the basis of clinical, epidemiological and experimental data, for physiological requirements
for energy and other nutrients (the most recent of these recommendations are contained in the
report FAO/WHO/UNU, 1985 Energy and Protein Requirements, 1986 Requirements of
Vitamin A, Iron, Folate and B 12).

RNIs are calculated in such a way as to ensure the best possible nutritional status (according
to the current state of knowledge) for the particular population at which the recommendations
are aimed. For all nutrients, with the exception of energy, they include a safety margin to take
account of individual variation, taking the form of the mean plus two standard deviations,
thus ensuring the levels will be adequate for 97.5% of the population. The RNI for energy is
fixed at the mean requirement, as excess energy intake can be an indication of malnutrition,
in the form of obesity.

Figure 2.2 shows the relationship between requirements and various reference values for all
nutrients with the exception of energy.


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