Definitions

The DRIs consist of the following nutrient-based reference values: Estimated Average Requirement (EAR), Recommended Dietary Allowance (RDA), Adequate Intake (AI), and Tolerable Upper Intake Level (UL). For macronutrients, there is also the Acceptable Macronutrient Distribution Range (AMDR) and the Estimated Energy Requirement (EER). The scientific data for developing DRIs consist of clinical trials and observations in humans and other studies including dose–response, balance, depletion–repletion, prospective observation, and case–control approaches. The EARs, RDAs, AIs, and ULs refer to average daily intakes over a number of days. The IOM describes each value in the following way:

This value is used as the basis for developing the RDA and can be used for assessing the adequacy of estimated nutrient intakes of individuals and groups and for planning intakes for groups.

In the case of energy, an Estimated Energy Requirement (EER) is provided.

The RDA can be used as a guide for daily intake by individuals. Intakes below the RDA, however, cannot be considered inadequate, because the RDA falls above the requirements of most people. It is based on an estimate of the average requirement plus an increase (typically two standard deviations above the EAR) to account for the variation within a particular group.

Individuals should use the AI as a guide for intake of a nutrient for which no RDA exists. The AI is an intake level that is derived through experimental or observational data that appears to sustain a desired indicator of health in a group (or groups) of apparently healthy people.

This value is not intended to be a recommended level of intake, and there is no established benefit for individuals to consume nutrients at levels above the RDA or AI. For most nutrients, this value refers to total intakes from food, fortified food, and nutrient supplements.

These values, which are estimated for fat, fatty acids, carbohydrate, and protein, are expressed as percent of energy since the requirement is not independent of other energy sources or the total energy requirement of an individual.

Figure 3-1 shows how the DRI values relate to the risks of either inadequacy or adverse effects. The DRIs provide a set of reference values for 12 life-stage groups for the United States and Canada. Similar sets of recommendations, typically called recommended dietary intakes, exist for other countries or in some cases for a worldwide audience (FAO/WHO, 2002, 2004).

Criteria for Setting Dietary Recommendations

The first edition of the Recommended Dietary Allowances, published by the National Academy of Sciences in 1943, provided recommended intakes for energy and nine essential nutrients. The RDAs were revised periodically based on new scientific knowledge and interpretations. With each revision there were changes in the numbers of nutrients considered and the levels recommended, but the basic philosophy was to define RDAs as levels sufficient to cover individual variations and provide a margin of safety above minimum requirements (IOM, 1994). In contrast, the criteria used to determine the DRIs goes beyond preventing a nutrient deficiency disease and also includes optimizing health, reducing the risk of chronic disease, and avoiding overconsumption of a nutrient (IOM, 2006). For example, the DRI for vitamin C is higher than simply the amount to prevent scurvy. It also considers the amount needed for antioxidant protection and tissue saturation while at the same time minimizing urinary loss. Like the former RDAs, the DRIs apply to the healthy general population and are not intended to apply to people who have an acute or chronic disease or who are already malnourished.

Other countries with recommended dietary intakes have also debated how to define their levels—should they use a minimal amount that prevents deficiency disease in all healthy people, an intermediate amount that allows for a large margin of safety, or a level that supports optimal nutrition? For example, when setting the requirement for vitamin C, Australia and New Zealand considered several criteria, including biochemical indices, clinical outcomes, vitamin C turnover, and interactions with other protective phytochemicals in fruits and vegetables. Going on the strength of the evidence, the final recommendation was set based on the prevention of scurvy, vitamin C turnover, and biochemical indices of vitamin C status, such as in plasma, urine, and leukocytes. However, it was not based on the potential interaction with other food components eaten at the same time (National Health and Medical Research Council, 2006).

The use of professional judgment and interpretation to set an RDA, DRI, or other recommended intake is illustrated by the range of values for some nutrients in sets of standards in different countries. For example, a review of nutrient requirements for children in 29 European countries found a twofold to fourfold difference among countries in their established reference values for vitamin and mineral requirements (Prentice et al., 2004; Pavlovic et al., 2007). Although different standards may be due in part to biology, much of the difference can be explained by the varied approaches used in setting the standards. The IOM has examined the conceptual framework used to develop the DRIs and has identified ways the development process could be enhanced (IOM, 2008).

How DRIS are Used

The various DRI values relate to the distribution of requirements and the distribution of intakes, and they can be used to both assess and plan diets of individuals and groups. Dietary assessment is done to determine if the nutrient intake of an individual or group meets their nutrient requirement. Dietary planning is used to recommend a diet that provides adequate, but not excessive, levels of nutrients for either an individual or a group (IOM, 2006). Figure 3-2 provides the conceptual framework for these uses, although using the DRIs to assess and plan diets of individuals is more challenging because the exact nutritional requirements of an individual cannot be readily determined. Both nutrient requirements and nutrient intakes are only estimates based on available data, so any assessment results or dietary recommendations are at best approximations. Nutrient intake data should be considered in the context of other data, such as clinical, biochemical, or anthropometric information.

Over the years, the former RDAs were often inappropriately interpreted as the amounts of essential nutrients a healthy individual needs over time. They were also used for several other purposes, including establishing nutrient standards for food assistance programs such as the National School Lunch Program and School Breakfast Program, evaluating dietary survey data, designing nutrition education programs, developing and fortifying food products, and setting standards for food labels (IOM, 1994). The DRIs were purposely developed to address some of the limitations and inappropriate applications of the former RDAs in assessing and planning diets. In general, EARs are used to assess intakes of both individuals and groups. If no EAR exists, the AI can be used in a limited way to assess intakes of individuals and groups. EARs can also be used for planning nutrient intakes of groups. RDAs should only be used as a guide for planning nutrient intakes of individuals. If no EAR (hence no RDA) exists, the AI can be used as a guide for planning nutrient intakes of individuals or as a target for the mean or median intake when planning for groups. The IOM has issued two separate reports describing in more detail how the DRIs can be applied to dietary assessment and planning (IOM, 2000b, 2003). Boxes 3-1 and 3-2 summarize how these applications differ between individuals and groups.

Development of Dietary Guidelines

Over the years as the relationship between diet and health became clearer, a new type of dietary advice emerged in the form of dietary goals and guidelines. Unlike the former RDAs, which focused on ensuring adequate intakes of essential nutrients, these guidelines emphasize the need to increase or decrease consumption of those food components that have been shown to affect the risk of certain chronic diseases. Another difference is that RDAs and DRIs state the amount (weight) of intake recommended on a daily basis for various nutrients with no indication of whether typical intake is high or low; whereas dietary guidelines often start with the estimated national diet and express recommended changes, generally in terms of increasing or reducing various foods and food components.

In the United States this shift in focus from obtaining adequate intakes to minimizing excessive intakes began in 1977 when a United States Senate Select Committee on Nutrition and Human Needs issued a set of recommendations known as the Dietary Goals for the United States (United States Senate, 1977). These goals provided quantitative recommendations on the amounts of complex carbohydrates, sugar, fat, saturated fat, cholesterol, and sodium that should be consumed. The Dietary Goals were controversial, in part because the diet plans developed to meet the goals were so different from the food patterns of typical Americans.

Subsequently, a new publication, Nutrition and Your Health: Dietary Guidelines for Americans, was jointly issued in 1980 by the USDA and the U.S. Department of Health, Education, and Welfare (now the U.S. Department of Health and Human Services [USDHHS]). This publication has been revised six times since 1980. The 1995 revision was the first one to be mandated by the government as a result of the National Nutrition Monitoring and Related Research Act (NNMRRA), which requires the Secretaries of Agriculture and Health and Human Services to review and jointly issue the Guidelines every 5 years (NNMRRA, 1990).

The purpose of the Dietary Guidelines is to translate information about individual nutrients and food components into an interrelated set of recommendations to help the public choose a healthy diet. The process used to create the Dietary Guidelines has evolved to include three stages: (1) an evidence-based review of the scientific literature; (2) the development of a policy document for professionals such as policy makers, nutrition educators, nutritionists, and health care providers; and (3) the development of messages and materials that communicate the Guidelines to the public. The seventh edition of the Guidelines—Dietary Guidelines for Americans 2010—provides recommendations that encompass two overarching concepts (USDA/USDHHS, 2010):

The policy document identifies 23 key recommendations for the general population and 6 for specific population groups, such as pregnant women and older adults. The key recommendations are intended as an integrated set of advice, grouped into four categories: (1) balancing calories to manage weight, (2) reducing intake of certain foods and food components, (3) increasing intake of certain foods and nutrients, and (4) building healthy eating patterns. Examples of key recommendations are “Prevent and/or reduce overweight and obesity through improved eating and physical activity behaviors” and “Reduce the intake of calories from solid fats and added sugars.” To help consumers implement the Guidelines, these recommendations are translated into consumer-friendly messages and materials by the USDA, USDHHS, and others.

The Dietary Guidelines have traditionally been intended for healthy Americans ages 2 years and over. However, the latest recommendations recognize the large percentage of Americans who are overweight or obese and/or at risk for chronic disease. Compared to previous Guidelines, the 2010 Dietary Guidelines place stronger emphasis on reducing calorie consumption and increasing physical activity and are intended for Americans ages 2 years and over, including those at risk for chronic disease. The Guidelines are not intended for younger children and infants, whose dietary needs differ.