Energy and nutritional requirements

Your energy requirements depend on various factors, including age, gender, physical activity, muscle mass, body temperature, and whether you are still growing. Pregnancy, breast-feeding, menstruation, illness, infection, how much you eat or sleep, and hormone levels are additional factors. In addition to identifying the types of nutrients we must include in our diets on a daily basis, we also need to know how much of each is required for optimum health.

Calculating energy requirements

Sedentary or bedbound people: 11.5cal per 450g (1lb) of body weight per day
People who only do light or routine activities: 13.5cal per 450g (1lb) of body weight per day
People doing moderate activities and a regular exercise programme: 16cal per 450g (1lb) of body weight per day
Those doing vigorous exercise, such as athletes, manual labourers, and patients recovering from injury: 18cal per 450g (1lb) of body weight per day.

Jargon buster

Metabolism

A collective term for all the chemical processes constantly occurring within the body, including those in which the nutrients from food are converted into substances that the body uses or excretes as waste.

Guidelines for nutritional requirements

Recommended daily amounts (RDAs) were originally set by the Department of Health in 1979 to specify how much of a certain nutrient was needed by different groups of the population. But RDAs were often used wrongly to assess an individual's diet.

The Department of Health replaced RDAs with DRVs (dietary reference values) in 1991, although we still use the familiar RDAs. They are benchmark intakes of energy and nutrients - they can be used for guidance, but shouldn't be seen as exact recommendations.

RDAs show the amount of energy or an individual nutrient that a group of people of a certain age range (and sometimes sex) needs for good health. Although RDAs are given as daily intakes, people often eat quite different foods from one day to the next, and their appetite can change, so in practice the intakes of energy and nutrients need to be averaged over several days. RDAs apply to healthy people only and don't apply to children under five years of age.

Information given on food labels must comply with EC Nutrition Labelling Regulations, which use Nutrient and Energy Intakes for the European Community (Commission of the European Communities 1993). These are often slightly higher than UK RDAs.

Dietary Reference Value (DRV)

Estimated average requirement (EAR): average amount of energy or a nutrient that is needed by a group of people.
Reference nutrient intake (RNI): amount of a nutrient that is enough to meet the dietary needs of about 97 per cent of a group of people.
Lower reference nutrient intake (LRNI): amount of a nutrient that is enough for a small number of people in a group with the smallest needs. (Most people need more than this.)
Safe intake (SI): recommended when there is not enough information on the physiological requirements for a nutrient.

In the Vitamin and Mineral Directories (see What are Vitamins?), the UK RDAs for healthy men and women are provided, followed by the RDA set by the European Community, wherever these figures are available.

Lisa Hark, PhD RD & Dr Darwin Deen

Posted 30.06.2010

ADS GOOGLE

See more in the dossier: Nutrition: why we need food