Chapter 2


1.4.1 Reference Nutrient Intakes for energy

RNIs for energy reflect the average requirement for the relevant population group, to avoid
recommending energy intakes which could lead to obesity. RNIs are given by gender and by
age group, which can then be aggregated, according to the proportions of the different
categories present in the population, to give national figures.

Energy intake can be measured in calories (Kcals.) or joules (Kjs.). I Kcal. is equivalent to
4.2 Kjs. In this chapter kilocalories will be used as the unit of measurement.

The energy content of food depends on its composition. One gramme of carbohydrate
contains 4 kcal, as does one gram of protein, whereas one gram of fat contains 9 Kcal. Energy
is used by the human body for the following purposes:

 To maintain body functions, breathing, circulation, temperature maintenance, while
 the body is at rest. The rate at which the body uses energy while it is at complete rest
 is defined as the Basal Metabolic Rate (BMR). BMR varies according to body
 weight.

 To sustain the chosen level of physical activity (PAL). In general, adjustment for the
 PAL will vary according to gender and as to whether lifestyle involves light,
 moderate or high levels of activity. In most developed countries, a PAL of 1.55 is
 applicable to most people, i.e. 1.55 times the BMR. This represents a sedentary
 lifestyle with desirable activity. A high level of physical activity at work and leisure
 would be represented by a PAL of 1.8 for women and 2.1 for men.

 To cover the energy costs of metabolising foods after meals. This is usually included
 in calculations of the BMR.

A generally accepted method of calculating the estimated average requirement for energy
(EAR) was proposed by FAO in 1986, based on the recommendations of a group of experts.
This takes into account the basal metabolic rate of the individual, adjusted for body weight
and the physical level of activity as follows:

 EAR = BMR PAL

To calculate the EAR or RNI (which are the same for energy intake) for a group of the
population the analyst must know the average weight of the population under consideration,
by age group. Based on this, the appropriate BMRs can be calculated, using the formulae
(according to Schofield's equation) given in Table 2.2.


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