Energy and reference values for European Children ( Prentice A et al Brit J Nutrition 2004, 92, S83-S146
National reference values for children aged 2 to 18 years across Europe are very varied.
The formulation of dietary reference values and nutritional recommendations require an understanding of the physiological requirements of a healthy individual.
The best definition of a physiological requirement should be
1.the amount and chemical form of a nutrient to maintain normal health and development without disturbance of the metabolism of any nutrient. An intake sufficient to meet physiological requirement which will differ between individuals
2. the amount of the nutrient or energy that will meet needs, in the environment in which the community lives using local foods.
The purpose of .nutritional reference values is to maintain and promote health and quality of life, and the vital metabolic and psychical and psychic functions in nearly all of the healthy individuals population. It is desirable to allow for the establishment of suitable body stores. Also to prevent nutrient-specific deficiency diseases .and deficiency symptoms.. but not in excess.
Central to the dietary reference values and recommendations is an understanding of the bioavailability of dietary nutrients; that is how much actually gets into the body and is available for metabolic and physiological functions. Bioavailability means the whole of absorption, distribution, metabolism and excretion. Bioavailability is affected by the composition of the diet, the chemical form of the nutrient and the nutritional status of the individual regarding that nutrient.
Bioavailability varies with age, with physiological state (e.g. puberty, pregnancy, lactation) and with nutritional status. For example, the absorption of many minerals increases during puberty and pregnancy, and excretion decreases. Metabolic adaptation in individuals with small body stores can lead to increased absorption efficiency in some situations but can also lead to smaller physiological requirements in others. Physiological requirements differ between different organ and tissues of the body.. A good example of this is the active transport of nutrients across the placenta in pregnancy.
The term Recommended Dietary Allowance for a nutrient was first used in 1941 to enable food rationing to be a safe policy for the population. The definition is the average amount of a nutrient which should be provided per head of a group of people if the needs of practically all of the population are to be met. Recommended has now been replaced by ‘reference value”.
Different countries have defined nutritional requirements, recommendations and reference values, and nutritional guidelines for their own populations. The guiding principle being that physiological requirements differ between individuals and that the handling of nutrients by the body may be substantially affected by environmental and individual factors.
The Scientific Committee on Food of the EU defined three reference values to describe the distribution of required dietary intakes within age- and gender-specific subgroups of the population:
1. The mean intake to meet the average physiological requirement, the Average Requirement (AR);
2. The 97.5th centile (mean + 2SD>, the Population Reference Intake being “theintake that will meet the needs of nearly all healthy people in the population or group”
3. The 2.5th centile (mean-2SD), the Lowest Threshold Intake , the intakebelow which nearly all individuals in the population or group will be unable to maintain metabolic integrity according to the criterion chosen”.
The UK used different terminology for the three Dietary Reference Values (DRV):
1. Estimated Average Requirement (EAR);
2. Reference Nutrient Intake (RNI = EAR +2SD)
3. Lower Reference Nutrient Intake (LRN1 = EAR —2SD).
All the definitions assume that the distribution is normal so that the standard deviation can be used to describe upper and lower values.
The USA/Canada, the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes (Food and Nutrition Board. 1997) adopted a similar framework for the derivation of Dietary Reference Intakes
1. Estimated Average Requirement (EAR) as ‘the average daily nutrient intake level estimated to meet the nutrient requirement of half the healthy individuals in a particular life stage and gender group”;
2. Recommended Dietary Allowance (RDA) as “the average daily nutrient intake level estimated to meet the nutrient requirement of nearly all (97 to 98 per cent) healthy individuals in a particular life stage and gender group’.
When there is insufficient data to confidently give a recommendation the US/Canadian committee defined Adequate Intake (AI). , the “recommended average daily nutrient intake level’, to be used ‘when an RDA cannot be determined’
In recent years, the concept of an upper limit has been introduced, to define nutrient intakes which might be excessive and detrimental to health,. In the EU . an Upper Tolerable Nutrient Intake Level and the USA/Canada (Food and Nutrition Board. a Tolerable Upper Level
- Martin Eastwood