|Food and Nutrition Bulletin Volume 04, Number 4, 1982 (UNU, 1982, 85 pages)|
A carpenter works with woods whose specifications he knows and measures them with a tape measure ruled in an international standard of length. Nutritionists work with food, about whose composition they have partial knowledge, and measure the nutrients in these foods against national standards, the recommended dietary intakes (RDls). Nutritionists in most countries do not have a complete national set of food composition tables; the tables available have to be supplemented with data from several other comparable countries and with unpublished data. Furthermore, most national standards of nutrient intake are not comparable and are sometimes out of date, and they differ among countries.
This paper considers the history, uses, and limitations of RDls, discusses how RDls are worked out, and looks at some trends in recent RDls and future possibilities.
Analytic comparison of the RDls for the different countries of the world has become the responsibility of Committee l/5 of the International Union of Nutritional Sciences (IUNS) - the Committee on Recommended Dietary Allowances. In 1975 the committee, under the chairmanship of Dr. W. Henry Sebrell, produced comparative tables for nine nutrients from 17 countries and 2 international bodies (1). The nutrients were energy, protein, vitamin A, thiamin, riboflavin, niacin, ascorbic acid, calcium, and iron. The countries were Australia, Canada, Colombia, the German Democratic Republic, the Federal Republic of Germany, Finland, India, Indonesia, Japan, Malaysia, the Netherlands, the Philippines, Thailand, Turkey, the United Kingdom, the United States, and the USSR; and the inter" national bodies were the Institute of Nutrition of Central America and Panama (INCAP) and the World Health Organization (WHO). The recommendations reviewed by the IUNS committee had been published between 1964 and 1973.
The next chairman of the committee, Dr. Arvid Wretlind, convened a round-table on Comparison of Dietary Recommendations in Different European Countries at the Second European Nutrition Conference, in Munich in September 1976 (2). There were six speakers from different regions explaining the views of different countries and a fully reported general discussion with some conclusions. A major part of the report is the assemblage of tables of recommended dietary intakes from 15 countries in West and East Europe (Czechoslovakia, Denmark, the Federal Republic of Germany, Finland, the German Democratic Republic, Hungary, Italy, the Netherlands, Norway, Poland, Romania, Spain, Sweden, the United Kingdom, and the USSR). A few of these countries do not have their own tables but reported that they use those from other countries.
The present Committee l/5 of IUNUS was reconstituted in 1979 under my chairmanship, with the charge "to publish an up-to-date tabulation and analysis of the RDAs of different countries." Our members have collected national, regional, and international recommendations from around the world. These come to 41 in all, the largest collection of dietary recommendations ever assembled. There are similarities and differences among the RDI reports. There are more similarities, but the differences perhaps attract greater interest. Most of the differences can be explained by:
- different ideas of the meaning and uses of RDls,
- different subdivisions of people into age, sex, and physiological groups,
- different criteria for nutritional adequacy, and
- different foods available and preferred in each country.
This is all against the background of inadequate quantitative basic data relating to human requirements for energy and nutrients under physiological conditions. The US dietary goals (3) evoked much interest, warm controversy, and a crop of similar sets of guidelines in several other countries. Tucked at the back of that report was a table that no one has challenged. It shows the gaps in our information about nutritional requirements. We reproduce it here in modified form as table 1.
It is not possible to reprint here the extensive tables and the recommended dietary intakes of each country, and most are so similar to the FAD/WHO and/or US recommendations that such reprinting would be of limited value. Readers are referred first to the FAO/WHO publication Handbook on Human Nutritional Requirements (4). (It should be noted that revisions in the requirements for protein and for dietary energy may be made as a result of recommendations of an FAO/WHO/UNU meeting held in Rome 5-17 October 1981.)
TABLE 1. State of Knowledge on Nutritional Requirements as of 1976
|Fatty acids (EFA)||||||||||||||+||+|||||
Source: US Department of Agriculture, Beltsville, Maryland.
= little or no data; + = fragmentary data; ++ = substantial progress made.
TABLE 2. Summary of Recommended Dietary Intakes for Young Men and Pregnant and Lactating Women
|For men, 26-29 years ||Addition for women, 23-30 years, during pregnancy||Addition for women, 23-30 years, during lactation|
(kcal x 10)
|+29.7||W. Pacific |
( - 5)
|Vitamin A |
(µg R.Eq. x 10)
|Vitamin D |
|Vitamin E |
|+0.29||W. Pacific |
|+2.2||W. Pacific |
|Vitamin B6 |
|2.03||9 countries |
(µg x 10)
|All others |
|Vitamin B12 |
|Vitamin C |
|41||W. Pacific |
(mg x 10)
*Either the figure taken as free folate or 50 per cent of the figure given for total folate is used.
A list of available national and regional dietary intake or allowance publications is appended to this introductory report (Appendix 1). These references make up the body of chapters 2 and 3 of the complete IUNS report. Chapter 4 consists of a summary table reduced to three sets of figures: RDls for men 26-29 years old, and the additions to be made during pregnancy and during lactation to the ordinary RDls for women 23-30 years old (which are generally somewhat lower than the RDls for men) This table, printed here in its entirety (table 2), shows at a glance:
- the number of countries giving a numerical recommendation for each nutrient,
- the world mean recommendation for each of 18 major nutrients,
- the country (or countries) with the lowest and the highest daily RDI (and the number in parentheses).
For example, 41 countries give an RDI for vitamin C for men in their late twenties. The world mean recommendation for this sex and age group works out to 47 mg/day. The lowest figure is 30 mg, recommended by 30 countries, while the highest recommendation is 95 mg/day, in one country (Bulgaria).
The evolution of dietary standards was described by Dr. Isobel Leitch in 1942 (5). Their original purpose was to prevent disease or to maintain health. The 1862 standard of Dr. E. Smith in England was research to prevent starvation and disease during the cotton famine in Lancashire. "What is the least cost per head per week for which food can be bought in such quantity and in such quality as will avert starvation-disease from the unemployed population?"
In the First World War a standard for energy requirements was devised by Lusk and used "to feed the army and nation. "
The British Medical Association's standards (1933) were formulated to maintain health and working capacity during the depression. The League of Nations standards (19351938) were designed "to marry health and agriculture." The first recommendations of the US National Research Council (1941) were produced to maintain perfect health. The aim was "buoyant health," the building up of our people to a level of health and vigor never before attained or dreamed of."
The United States has gone on revising its recommended dietary allowances (RDAs) about every five years, and an increasing number of other countries now have expert committees that publish their own national recommendations.
In the meantime, the RDls have been taken up by economists, food manufacturers, sociologists, politicians, journalists, and others and are now used in at least five different ways (6):
1. For assessing food intake of groups or Individuals RDls
provide a yardstick against which the diets of different sections of a community can be measured. In nutrition surveys, the cutoff between inadequate and adequate has often been set below the RDI. For example, in the US ICNND surveys (7) a "deficient" ascorbic acid intake for men was less than 10 mg/day, a "low" intake was 10 to 29 mg, "acceptable" 30 to 49 mg, and a "high" intake was above 50 mg/day. At the time (1964) the RDA for men was 70 mg/day. Similarly, in considering the adequacy of nutrient intakes by adolescents, it has become conventional to consider the percentage in a group who eat less than two-thirds of the RDI (8). The RDls are also used by dietitians for assessing the diets of individual patients. For example, Bennion's book (9) shows a dietary history form on which there is space for the estimated intake of 12 nutrients against the RDAs for the same individual.
2. For planning therapeutic diets or Institutional meals. RDls provide a guide for dietitians prescribing special diets for individuals. Unless used for a short time or in a desperate illness, an individual diet should provide the recommended intake for all essential nutrients except for the one(s) to be manipulated. Diet sheets ought to state this. For example, the low-protein diet in a current textbook (10, p. 554) includes the rubric: "Protein 40 g/day, energy 7.6-8.4 MJ (1800-2000 kcal), Na 40 mmol and K 60 mmol/ day. Adequate in other nutrients but iron and calcium need to be supplemented if used for a long time." Caterers in hospitals (for patients not on special diets) and housekeepers in long-stay homes, boarding schools, and colleges usually work from menu cycles that are often passed from one person or place to another, with modifications from time to time. But if there should be a complaint about under-feeding, the recommended intakes would have to be used as the standard. RDls have sometimes been used in working out the nutritional standards for school meals. The 1975 British standards for the school lunch (11) were based on 33 per cent of the recommended intake for energy and 42 per cent (half-way between 33 and 50 per cent) of the recommended protein intake.
3. For planning national food supplies. RDls should provide a target in planning food supplies and policies for a developing nation. They are used by international agencies for comparing different underdeveloped countries to see which has greater need for aid. Thus, they provide common ground between economists and nutritionists. The recommended intakes are the fairest basis for calculating rations for use in time of food shortage. In a famine, proportions short of the full RDI can be used so that each can be given emergency subsistence levels or temporary maintenance amounts of food (10, p. 502).
4. As the denominator for nutrition labelling. In nutrition labelling, the major components in an amount of food, usually a standard serving, have to be compared with a standard. In the United States, which has gone further than other countries with nutrient labelling, the labelling standards laid down by the Food and Drug Administration are based on the RDAs for particular age and sex groups. For adults the highest values for males or females in the 1968 RDAs have been used. Commonly, the amount of nutrient in a standard serving is expressed as a percentage of the RDI. One serving (30 g) of a breakfast cereal, for example, may be seen to contribute 28 per cent of the recommended intake of thiamin and 36 per cent of the riboflavin recommendation,
5. As the basis for a nutrient density index to express the nutritional quality of foods. Nutrient density is a useful concept for nutrition education and for trying to express the nutritional quality of foods. When the ratio of a nutrient to the energy is the same as the respective recommended intakes, the density of the particular nutrient is said to be 1. This should be worked out for the appropriate age and physiological state. For men 18-35 years old, the Australian recommendation for vitamin C is 30 mg and for energy 11.6 MJ (2,700 kcal); so a food containing 11 mg of ascorbic acid/1,000 kcal (4.2 MJ) has a nutrient density of 1. If a food contains more ascorbic acid per energy, then it is, as it were, a vitamin C donor in the diet; if it contains less ascorbic acid, it does not provide its fair share, and unless it is a good source of other nutrient(s), the food may be considered less nutritious than average. Foods like sugar, fats, and alcohol are in this category. In this way, R.G. Hansen and colleagues in Utah have worked out how to calculate a nutritional quality index for foods (12). The same concept can then be used to evaluate new types of manufactured foods and the enrichment of foods with synthetic nutrients. The Council of Foods and Nutrition of the American Medical Association (13) suggested that formulated foods that cannot easily be compared with a conventional food should contain, per serving, the major nutrients in at least the same ratio to energy as in the recommended intakes.