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Overview of the DRI Process

OVERVIEW OF THE DIETARY REFERENCE INTAKES

The Dietary Reference Intakes (DRIs) are a set of reference values that encompass a safe range of intake and provide recommended nutrient intakes for the United States and Canada. The DRI concept developed from discussions about how future Recommended Dietary Allowances (RDAs) should be revised. This issue was covered during the 1993 workshop How Should the RDAs Be Revised (IOM, 1994), by the UK Committee on Medical Aspects of Food Policy (COMA, 1991), and as part of a statistical probability concept for nutrient adequacy developed by George Beaton (Beaton, 1991).

The DRI concept offered a new approach that extended nutrient intake recommendations beyond the goal of nutritional adequacy and the prevention of deficiency disease to include public health concerns about chronic disease and overconsumption. This concept:

• Applies a model based on probability and risk to derive a panel of reference values;
• Sets a safe upper intake level to reduce the risk of adverse health effects related to overconsumption of a nutrient; and
• Considers the potential role for nutrients or other food substances in reducing the risk of chronic disease.

Most of the first DRI values were based on biological indicators related to inadequate intakes of nutrients. In recent decades, concern

about nutritional deficiency disease within population groups has been replaced with concern about the role of diet on the risk of chronic disease. Weight gain occurs when energy intake exceeds energy expenditure. Such long-term energy intake imbalances are one type of dietary imbalance associated with the risk of chronic diseases. In response, as DRI nutrients have undergone review, the derivation of DRI values has evolved to include consideration of chronic disease risk reduction.

THE DRI ORGANIZING FRAMEWORK

The concept of a DRI organizing framework was introduced at a 2007 workshop, The Development of DRIs 1994–2004: Lessons Learned and New Challenges (IOM, 2008). The framework includes the need for a science base that not only addresses information needs in a way that allows for integration into program and policy initiatives but that also presents information in a predictable format so users can easily find topics of particular interest. This requires a standardized format with transparency and documentation of decision making throughout the organizing process.

The framework is adapted from guidance for organizing scientific deliberations to assess DRI components in a way that is useful to sponsors and maintains the scientific integrity of the assessment process (NRC, 1983). The core concepts of the framework relevant to energy are that (1) an incomplete evidence base is expected in a DRI review and uncertainties need to be dealt with by documentation and the use of scientific judgment and (2) the needs of users of the DRIs are a key component of the framework.

The first step in the framework, literature reviews and interpretation, is used to identify and assess indicators of nutrient adequacy or toxicity across age and sex groups in the population. This step includes a review and synthesis of evidence on relevant health outcomes. The strength and quality of the evidence is critical to establishing a rigorous evidence base to support the identification and assessment of indicators of both adequacy and excess.

For energy, doubly labeled water (DLW) databases were selected as the primary evidence base for estimating energy requirement equations. An umbrella review of systematic reviews was used as a source of evidence to understand relationships between energy intake and health outcomes.

The second step in the organizing framework is to identify intake–response data for the nutrient or outcome of interest and to use these data to derive DRI reference values for the DRI life-stage groups. For energy, the Estimated Energy Requirement (EER) is the DRI value. It is derived from well-controlled studies using DLW in which the energy expenditure of individuals is determined.

The third step in the framework is intake assessment. In this step, population-based intake data and/or biological indicators of nutrient status are used to assess intake adequacy or inadequate or excessive exposure levels for a nutrient. National surveys or other large population databases are generally used to obtain population-based intake data.

The last step in the framework considers the public health consequences of either not meeting or exceeding a recommended intake. This includes determining how characteristics unique to a population age/sex group, such as body size, lifestyle, environment, or other factors, could influence nutrient requirements for that group. This DRI organizing framework provides a systematic approach to deriving the DRIs. Further, it supports documentation of the strength and sufficiency of the evidence, enhances transparency, and allows for incorporation of new and emerging scientific tools into the process (IOM, 2011; NASEM, 2019).

A proposed analytic approach to implementing the framework described the link between nutrient exposure and clinical or disease outcome for which a strength of association could be defined. In this model, if a strong evidence base for the clinical or disease outcome is lacking, an indicator marker and/or surrogate marker could be identified that best predicted the clinical outcome (Russell et al., 2009). For example, bone growth is a surrogate marker for phosphorus status. Body weight is an indicator of energy intake balances or imbalances.

When the DRIs for calcium and vitamin D and for sodium and potassium were updated in 2011 and 2019, respectively, the DRI framework was revised to provide a more rigorous and transparent approach to deriving DRI values (IOM, 2011; NASEM, 2019). Specifically, the framework was modified to (1) ensure greater transparency in the decision-making process and (2) provide options for decision making when data needed to support such decisions are limited (i.e., in conditions of uncertainty).

Systematic evidence reviews were introduced in the updated review of DRIs for calcium and vitamin D to provide a rigorous, transparent, and reproducible approach to establishing an evidence base from which to derive DRI values. The systematic review process for DRIs for calcium and vitamin D was refined to include risk-of-bias assessment and the Grading of Recommendations, Assessment, Development and Evaluations (GRADE)¹ system to assess evidence quality. In addition, a formalized approach to identifying an intake range or target goal for reducing risk of chronic disease was introduced with the DRIs for sodium and potassium. This resulted in a new DRI value—the Chronic Disease Risk Reduction (CDRR) value (Table 1-1).

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¹https://www.gradeworkinggroup.org/ (accessed November 11, 2022).

These revisions to the DRI organizing framework have increased the scientific rigor and transparency of the process for deriving reference values. However, despite the additional steps to the framework, absolute certainty does not exist in terms of the state of the science or the strength of evidence to support decision making. When evidence is limited and a lack of guidance could have implications for public health, an informed scientific judgment grounded in transparent and judicious documentation becomes necessary.

ADAPTING THE DRI ORGANIZING FRAMEWORK TO ENERGY

As noted above, the core statistical concept on which the Estimated Average Requirements (EARs) and RDAs are based is a distribution of requirements, meaning a variability in requirements among individuals in a given age/sex group. The EAR is the average intake requirement that meets the requirements of 50 percent of individuals in an age/sex group. The RDA represents intakes that meet or exceed the requirement for 97.5 percent of that group. For most nutrients, the requirements are normally distributed so that the RDA represents 2 standard deviations above the average requirement. Observed intakes for population groups also have distributions. These two separate distributions need to be taken into account when evaluating the adequacy of, or planning for, group or individual intakes.

For all nutrients except for energy, the adequacy of a group’s intake for a given nutrient can be evaluated by comparing the usual mean intake of that group to the mean requirement for that group (i.e., the EAR). The prevalence of nutrient inadequacy is estimated as the proportion of the age/sex group with usual intakes below the EAR (IOM, 2000). For individuals, usual intake above the EAR is assumed to be adequate. These quantitative relationships are not directly applicable to energy. While the EAR is the midpoint of the distribution of requirements of a broad age/sex group, the EER is an estimate of the midpoint of a range of requirements that applies to individuals of the same sex, age, height, weight and physical activity level (PAL) category. Furthermore, because energy requirements and intakes are correlated, the prevalence of inadequacy cannot be estimated by determining the proportion with self-reported intakes below the EER. Additionally, unlike other nutrients, the energy requirement distribution does not relate to any other DRI value, such as RDA or Tolerable Upper Intake Level (UL), which do not exist for energy.

For most nutrients, intake–response assessments are used to identify the EAR for a DRI age/sex group, and data on variability are considered to establish the RDA at an intake level that meets or exceeds the needs of almost all individuals in that group. Although consuming an intake level at or above the RDA exceeds the requirements of almost everyone, no risk

occurs unless the intake level exceeds the UL. However, this approach is not appropriate for energy, as there are adverse consequences (e.g., weight gain) for individuals whose energy intake exceeds their energy expenditure (i.e., their requirement).

It is also not useful to compare an individual’s self-reported energy intake with a calculated expenditure owing to bias in self-reported intake data, as well as the inherent variability in energy expenditure among individuals with similar characteristics. Rather, weight is frequently used as an indicator of the relationship between energy intake and energy expenditure. Body mass index (BMI) is then calculated to screen and categorize individuals and groups. BMI values outside of a defined normal range serve as an indicator of overconsumption or underconsumption of energy and can be used in calculating the EER for various age/sex groups (see Chapter 5). An additional complication is that energy balance is now known to be moderated by diet-related elements other than carbohydrate, protein, fat, and alcohol, namely the microbiome and dietary fiber (see Chapter 4 for factors affecting energy expenditure). Because the DRI organizing framework had not been developed when the first DRIs for energy were established, this committee had the challenge of developing a framework that was responsive to and appropriate for current topics and key areas relevant to energy.

REFERENCES

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