Title: The theoretical basis for Dietary Reference Values (DRVs), and their practical uses.
Key words: COMA, Recommended Daily Intake (RDI), Recommended Daily Allowance (RDA), dietary surveys, food labelling, population, individuals, energy, protein, fats, sugar, starches, vitamins, minerals, sugar, non-milk sugars, fruit, vegetables,
Date: May 2001
Author: Dr M Draper
The theoretical basis for Dietary Reference Values (DRVs), and their practical uses.
The expert Working Groups set up by the Commitee on Medical Aspects of Food Policy (COMA) in 1987 initially reviewed published Recommended Daily Intakes (RDI) (1) and Recommended Daily Amounts (RDA) (2) in 1969 and 1979 respectively and in 1991 produced its guidelines on DRV's which were more comprehensive and set a range of values ( see appendix for definitions).
Theoretical basis of Dietary Reference Values;
The 1969 and 1979 reports based their recommendations on single figures, defined as RDI's and RDA's respectively and carried the potential for misuse and misinterpretation. They were set deliberately high (compared to average requirements) to minimise the risk of under nutrition and due to their design, to apply to groups of people rather than individuals.
The new values (DRV's) represented the Panels best estimates of a range of intakes for various groups with the intention that these figures could be used as yardsticks for the assessment of dietary surveys and food supply statistics: to provide guidance on appropriate dietary composition and meal provision; or for food labelling purposes.
The estimates of requirements for the population were to be used as guidelines not as recommendations and assumed that the distribution curve for the parameter was normal or Gaussian. ( LRNI - EAR -RNI).
The panel did not use any single criterion to define these requirements and based the values on reliable experimental evidence, associations and epidemiological data. For most nutrients the panel found insuffient data to establish guidelines with any great confidence. The published figures therefore are to a certain extent hypothetical (best guess) and arrived at by informed consensus of the panel using the available scientific data and accepting the uncertainties relating to the appropriate parameter because of the difficulty in defining adequate intakes.
The panel attempted to set DRV's for energy, protein, fats, sugars, starches, non-starch polysccharides ( NSP), 13 vitamins, 15 minerals and considered 18 other minerals.
The DRV's are more elaborate and distinctive, clarifying potential confusion and misinterpretation regarding reference values such as 'total sugar and non-milk sugars', 'sodium and salt', 'total fat and saturates' , 'fibre and NSP'.
Practical uses of Dietary Reference Values;
It is reasonable to claim that the COMA report on DRV's improved the scientific basis for making practical dietary guidelines for the following reasons;
(a) the information on nutrients looked at the concept of health not merely the avoidance of deficiency diseases.
(b) it took a new approach by defining more than one figure for each nutrient thus recognising the broad range of requirements of individuals within a population.
(c) although the criteria to determine the values was not always backed by strong evidence it was judged to be the best possible and set a framework for amendments as new information from research becomes available.
The COMA report provided the scientific basis for the following practical dietary messages (4);
# If a varied diet ; including low-fat milk and diary foods, lean meat, fish and alternatives, bread, other cereals and potatoes, fruits and vegetables is eaten then the requirements for vitamins and minerals should be met.
# to increase fibre-rich starch foods.
# to increase consumption of vegetables and fruit.
# to reduce intake of sturated fats from animal sources and those added to cakes, biscuits and pastry.
# to use oils rich in monosaturates or polyunsaturates.
# that for most of the population vitamin and mineral supplements are not required.
The improved scientific basis for setting the DRV's has made it easier to interpret the findings in the National Diet and Nutritional Surveys ( see B4) and to assess the adequacy of intakes for particular groups. Targeted messages can now be aimed at particular at risk groups to improve the health of the nation.
Recommended Daily Intake (RDI) The amounts sufficient, or more than , for the nutritional needs of practicallly all healthy people in a population. ( Eaten as food).(1)
Recommended Daily Amount (RDA) The average amount of a nutrient, which should be provided per head to a group of people if the needs of practically all members of the group are to be met. ( Average for a group) (2)
Dietary Reference Values (DRVs) The collective term to cover all figures below EAR, RNI, LRNI .It includes guidance on high intakes, and is presented as average requirements for a normally distributed population. (3)
Estimated Average Requirement (EAR) The estimated average requirement (notional mean ) of a group for a particular nutrient.
Reference Nutrient Intake (RNI) The amount of a nutrient ( EAR + 2 Standard deviations) which is sufficient for almost all individuals ( 97.5%). It by definition exceeds the requirement of most people and habitual intakes above RNI are almost certainly adequate.
Lower Reference Nutrient Intake (LRNI) The amount of nutrient or energy
(EAR minus 2SD) which is sufficient for only a few individuals ( 2.5%). Habitual intakes below the LRNI by an individual will almost certainly be inadequate.
(1) Department of Health and Social Security (1969) Reports on public health and medical subjects No.120. Recommended Intakes of Nutrients for the United Kingdom. HMSO, London.
(2) Department of Health and Social Security (1979) Reports on health and social subjects No 15. Recommended Daily Amounts of Food Energy and Nutrients for Groups of People in the United Kingdom. HMSO, London.
(3) Department of Health (1991) Report on Health and Social Subjects No.41.Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. HMSO, London.
(4) Scientific Basis of Nutrition Education ( 1996) Nutrition Briefing Paper.