Interpretation and uses of dietary recommendations
When using dietary recommendations, several important points need to be considered.
The nutrient levels recommended are per person per day. However, in practice this will usually be achieved as an average over a period of time (days, weeks, or months) owing to daily fluctuations in the diet. As stated above, the setting of a range of dietary recommendations should encourage appropriate interpretation of dietary intake data, rather than the inappropriate assumption that the value identified to meet the needs of practically all healthy people is a minimum requirement for individuals. If an individ-ual’s nutrient intake can be averaged over a sufficient period then this improves the validity of the compari-son with dietary recommendations. However, in the case of energy intakes, such a comparison is still inap-propriate: dietary reference values for energy are intended only for use with groups, and it is more useful to compare an individual’s energy intake with some measure or calculation of their expenditure in order to assess adequacy.
In the case of a group, the assumption can be made that the quality of the diet can be averaged across the group at a given time-point, and therefore that appar-ently healthy individuals within a group may com-pensate for a relative deficiency on one day by a relative excess on another. It should also be remem-bered that allowances may need to be made for body size, activity level, and perhaps other characteristics of the individual or group under consideration, since the recommended intakes are designed for “reference” populations.
Another assumption made when setting recom-mendations for a particular nutrient is that the intake of all other nutrients is adequate, which in an appar-ently healthy population eating a varied diet is prob-ably reasonable.
Recommendations are not intended to address the needs of people who are not healthy: no allowance is made for altered nutrient requirements due to illness or injury. For example, patients confined to bed may require less energy owing to inactivity, and may require higher micronutrient intakes because of an illness causing malabsorption by the gut. Certain nutrients may also be used as therapeutic agents, for example n-3 fatty acids can have anti-inflammatory effects. These clinical aspects are considered elsewhere in these texts.
One complication arising in the formulation of dietary recommendations is caused by the fact that various groups of people within a population may have different nutrient requirements. Therefore, the population is divided into subgroups: children and adults by age bands, and by gender. For women, allow-ances are also made for pregnancy and lactation.
Infants are recommended to be fully breast-fed for the first few months of life. This poses a problem for the bodies setting the dietary recommendations, which have to set standards for those infants who are not breast-fed. The dietary recommendations for formula-fed infants are based on the energy and nutrients supplied in breast milk, but, because the bioavailability of some nutrients is lower in formula than in breast milk, the amounts stated appear higher than those that might be expected to be achieved by breast-feeding. This should not therefore be inter-preted as an inadequacy on the part of human (breast) milk compared with formula milks, but rather the reverse.
The dietary recommendations for infants post-weaning and for children and adolescents are gener-ally based on less robust scientific evidence than those for adults, for whom much more good information is available. In the absence of reliable data, values for children are usually derived by extrapolation from those of young adults. The calculation of nutrient requirements is generally based on energy expendi-ture because metabolic requirements for energy prob-ably go hand in hand with those for nutrients in growing children. In the case of infants post-weaning on mixed diets, values are obtained by interpolation between values known for infants younger than 6 months and those calculated for toddlers aged 1–3 years. Thus, the dietary recommendations for children and adolescents need to be approached with some caution, being more suitable for planning and labeling purposes than as a description of actual needs.
Finally, assessment of the dietary adequacy of people at the other end of the population age range is made difficult by the lack of data on healthy elderly people. One of the normal characteristics of aging is that various body functions deteriorate to some extent, and disease and illness become more common as people age. Until more data are available, the assumption is made that, except for energy and a few nutrients, the requirements of the elderly (usually defined as those over 65 years old) are no different from those of younger adults.
Bearing the above points in mind, dietary recom-mendations can be useful at various levels.
Governments and nongovernment organizations (NGOs) use dietary recommendations to identify the energy and nutrient requirements of popula-tions and hence allow informed decisions on food policy. This could include the provision of food aid or supplements (or rationing) when the diet is inadequate, fortification of foods, providing appro-priate nutrition education, introducing legislation concerning the food supply, influencing the import and export of food, subsidies on certain foods or for producers of food, and so on.
The food industry requires this information in the development and marketing of products. The industry is aware of consumers’ increasing interest in the nutritional quality of the food that they buy, and has responded by providing foods to address particular perceived needs, and more informative food labels.
●Researchers and the health professions need to assess the nutritional adequacy of the diets of groups (or, cautiously, of individuals) by compar-ing dietary intake survey data with the dietary refer-ence values . Once the limitations of the dietary assessment data have been taken into account, this information can be used to attempt to improve people’s nutrient intakes by bringing them more into line with the dietary recommendations. The formulation of dietary advice or guidelines depends on an appreciation of the existing situation: the solution can only be framed once the problem is characterized.
●Institutions and caterers use dietary recommenda-tions to assess the requirements of groups and devise nutritionally adequate menus. This is a great deal more easily said than done, mainly because of the financial constraints involved and, often, the food preferences of the population being catered for.
The public needs this information to help in the interpretation of nutrition information on food labels that may describe nutrient content in both absolute terms (g, mg, etc.) and as a percentage of the recommended dietary allowance (RDA) for that nutrient (usually per 100 g or per “serving”). It is thought that the latter is more meaningful to con-sumers, even though the concepts involved in setting the dietary recommendations are rather complex (making it difficult to judge which level of recommendation should be used as the standard) and they can be open to misinterpretation . Since 1998, some UK manufacturers and retailers have provided information about guide-line daily amounts (GDAs) for energy, some nutri-ents, salt, and fiber. These were developed by the Institute of Grocery Distribution (IGD, a UK research and training body for the food and grocery chain) and are derived from the DRVs [and the British Committee on Medical Aspects of Food Policy (COMA) and Scientific Advisory Council on Nutrition (SACN) recommendations for salt intake], but are much simplified. Unless consumers are provided with nutrition information in the most appropriate form on food labels, they cannot make informed choices as to what foods to buy and eat to meet their own perceived needs. At the very least, consumers should be able to compare prod-ucts to get their money’s worth.