Questions from the Federal DRI Joint U.S.–Canadian Working Group
In open session discussions held on February 24 and April 8, 2022, between the standing committee, the Federal DRI Joint U.S.–Canadian Working Group (working group), and the DRI committee, specific questions were posed. Those questions from the working group and the standing committee’s responses follow.
Question WG1: Who Should Be Included in the “Healthy Population” Definition to Adequately Characterize the Population Covered by the DRIs?
In support of the question, the working group provided the following context:
The phrase “apparently healthy population” (or “general population” or “healthy population”) has been used by DRI committees to define the population covered by the DRIs. These were defined as specifically excluding individuals who (1) have a chronic disease that needs to be managed with medical foods, (2) are malnourished (undernourished), (3) have diseases that result in malabsorption or dialysis treatments, or (4) have increased or decreased energy needs because of disability or decreased mobility (personal communication, Cindy Davis, open session held February 24, 2022).
To respond to this question, the standing committee reviewed the history of the use of terms such as “healthy populations” (Table 3-1) as well as the report, Guiding Principles for Developing Dietary Reference Intakes Based on Chronic Disease (NASEM, 2017). The report provided recommendations that pertain to the definition of “apparently healthy population.” The standing committee agrees with the population included in the definition: “(1) that an ‘apparently healthy population’ includes a substantial proportion of individuals who have obesity and other chronic conditions, such as hypertension or diabetes [and] (2) risk of developing such chronic conditions” (NASEM, 2017, p. 30).
The guiding principles committee further stated:
“Therefore, this recommendation for a formal approach to adding chronic conditions to the DRI process begins with clarification that the ‘apparently healthy’ population of interest includes people at risk of or with chronic conditions who do not meet the DRI exclusion criteria that exist at that time” (NASEM, 2017, p. 30).
A key phrase embraced by the standing committee is “who do not meet the DRI exclusion criteria that exist at that time.” As exclusion criteria may differ from nutrient to nutrient or nutrient group to nutrient group, the standing committee advises that each DRI committee establish exceptions that apply specifically to the nutrient or nutrient group that they have been asked to review (see more discussion on this point below). These exceptions should be limited to those conditions or medications that alter the requirements of the nutrient under review and its particular homeostatic or physiologic characteristics or features.
Question WG2: Is It Assumed That Subpopulations with Risk Factors for Chronic Diseases (Such as Overweight or Obesity, High Blood Pressure, Hypercholesterolemia, or Prediabetes) Are Considered to Meet the Current Definition Since They Do Not Meet the Exclusion Criteria Listed Above?
Unless a DRI review committee has reason to specifically exclude certain subpopulations, the standing committee recommends that those at risk of chronic disease should be included in the review committee’s deliberations. However, DRI committees should also be mindful that individuals within subpopulations that are at risk for, or who have, a chronic disease and are also taking medications that alter the absorption
or metabolism of the nutrient(s) under consideration should be exclusions. For example, those taking drugs for chronic conditions should be excluded only if the evidence suggests the metabolic effects of the drug alter their requirement for the nutrient under review. There also may be individuals undergoing procedures that may alter gastrointestinal function (e.g., gastric bypass surgery) who might need to be excluded. Each DRI committee, in consultation with the standing committee, should define and justify relevant specific exceptions early in its deliberation process (see response to question WG4 below). Exceptions should be documented in a “special considerations” section in the report.
Question WG3: How Should Overweight and Obesity Be Considered Given the High Prevalence of Obesity?
The standing committee advises that DRI committees should include populations with overweight and obesity because they sometimes represent a large segment of the population. However, when individuals with overweight and obesity also have severe comorbidities and other metabolic disorders, they may be excluded from the population if there is evidence that their condition or medications alter their energy or other nutrient requirements.
Question WG4: Should a Different Term Be Considered Other Than “Apparently Healthy Population” Since the DRIs Are Developed to Determine the Recommended Intake of Nutrients to Meet the Needs of the Majority of the General Population and the Health Status of This Population Has Shifted?
This standing committee concluded that the term “apparently healthy population” inadequately describes the population that should be covered by DRI values and thus recommends the term “general population” instead. This term is more inclusive of the population for whom the DRIs are intended to apply. Any population subgroup for whom reference intakes would not be appropriate should be determined on a nutrient-by-nutrient basis. The basis for these exceptions is whether there is evidence that a particular disease, health condition, disability, or medication is likely to alter the requirement for the nutrient under review. The purpose of seeking advice from the standing committee is to ensure a consistent approach across DRI review committees when defining exclusions.
The standing committee further concluded that the previously used term “exclusions” should be replaced with the term “exceptions” to describe characteristics in the subpopulation group(s) not to be included in the general population. As shown in Box 4-1, the term “exclusions” may be used when referring to data in the review process, whereas the term “exceptions” should be used when referring to decisions made for subgroups and populations. Future DRI review committees should seek advice from the standing committee on the selection of exceptions within the general population for the specific nutrient under review and those decisions documented in a special considerations section of the report.
Question WG5: How Should, or Can, Evidence from Populations That Are Not “Apparently Healthy” Be Used to Develop the DRIs? What about Data from Populations with Clinical Disease?
The standing committee recommends that future DRI review committees use the same criteria that they established for describing their “general population” when deciding on evidence during scoping reviews, systematic reviews, or meta-analyses of the literature. Importantly, the data on those with conditions or prescribed medications that alter nutrient absorption or metabolism leading to modified requirements may be considered as exclusions for determining nutrient-specific DRIs.
Question WG6: How Should This Definition Inform the Use of the DRIs for Their Various Purposes?
Recommendations for applications (uses) of the DRIs are a critical translational step in the DRI process for health care professionals and for establishing food-based guidance such as the Dietary Guidelines for Americans. Because factors affecting requirements vary among nutrients, specific exceptions for “general population” coverage should be determined on a nutrient-by-nutrient basis. Specific exceptions and their rationale should be clarified at the beginning and throughout each report. Guidance on how to manage exceptions should be included under a special considerations section at the end of the DRI report.
In addition to the predetermined life-stage groups, other subpopulations might be needed for specific nutrients. For example, recommendations for iron might subdivide the “general population” by dietary patterns with specific recommendations for vegetarians or vegans who are not likely to consume heme iron, a more bioavailable form of iron than nonheme iron (Dainty et al., 2014; Hurrell and Egli, 2010). Similar considerations may be appropriate for vitamin B12 (IOM, 1998; Neufingerl and Eilander, 2021). This approach is not novel, as past DRI review committees have made separate recommendations for specific subpopulations. For example, higher vitamin C requirements were established for smokers (IOM, 2000), and dietary supplements were recommended for B12 for vegans (IOM, 1998).
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