3

Defining the DRI Population

Since the first edition of the Recommended Dietary Allowances (RDAs) were published in 1941 (NRC, 1941), RDA committees have provided context to the intended populations for their recommendations, often referred to as “healthy populations” or “apparently healthy populations.” This definition was also used for dietary recommendations from the Canadian Council on Nutrition (Canadian Council on Nutrition, 1949). More recently, the joint U.S. and Canadian Dietary Reference Intakes (DRIs), the European Food Safety Authority (EFSA, 2022), and the Nordic Nutrition Recommendations (Christensen et al., 2020), among others, used similar descriptions. Table 3-1 provides examples of definitions of “healthy populations” adapted from nutrient recommendation reports of various governmental agencies and other health advocacy organizations. Up through the 1989 RDAs, the primary focus was on preventing dietary deficiency diseases by providing adequate amounts of essential nutrients; individuals with chronic diseases were excluded from the apparently healthy population (NRC, 1989).

Over the past 25 years scientific evidence has evolved that supports the association of dietary intakes with chronic disease risk and increasing availability of dietary guidance for reducing the risk of chronic diseases separate from the RDA process. This led to the recommendation by the Institute of Medicine (IOM) in a 1994 report that future RDAs include guidance on chronic disease risk reduction (IOM, 1994). Despite this, the use of the term “healthy” or “apparently healthy” populations to define the covered population was retained.

TABLE 3-1 Comparison of Definitions of Intended Populations in Reports on Nutrient Intake Recommendations

NOTE: DRIs = Dietary Reference Intakes; DRVs = Dietary Reference Values; EFSA = European Food Safety Authority; RDAs = Recommended Dietary Allowances; RNIs = Recommended Nutrient Intakes.

The subsequent dilemma for DRI review committees was how to apply the imprecise terminology and definition of terms such as “healthy” or “apparently healthy” populations to DRI values related to chronic disease risk reduction. This issue is particularly relevant given the shift in U.S. and Canadian adult populations so that a majority have, or are at risk of, a chronic disease and thus not considered “healthy.” For example, individuals diagnosed with hypertension or hypercholesterolemia might not be considered healthy but would benefit from reductions in intakes of sodium or substituting unsaturated for saturated fats, respectively. Additionally, many individuals do not maintain a body mass index (BMI) within the recommended range of 18–25 kg/m², and consequently may or may not be considered as clinically “healthy” (Lloyd-Jones et al., 2022; Petersen et al., 2019). These common conditions contribute to the problem of who should be included in the population for whom the DRIs are intended. The concern about not including the majority of U.S. and Canadian populations and the risk of inconsistencies regarding population groups needs to be considered in future DRIs.

Most weight-related chronic disease data use terminology for overweight and obesity that often is defined by BMI category. Other criteria such as body composition and adipose tissue distribution (adiposity) contribute to comorbidities associated with chronic disease risk (De Lorenzo et al., 2020; Hill et al., 2018) and may be more accurate criteria than BMI alone. However, BMI data are traditionally reported, and this report uses that metric as a proxy for adiposity. A reason to use BMI is that the mea-

sures are straightforward and consistently applied among investigators. Measures of body composition can vary considerably depending on the method used and calibration of the machine.

Many individuals with diet-related chronic conditions, including those who are treated with some medications, will likely benefit from dietary modifications. These individuals should be included in the population covered by future DRIs, unless there is evidence of an effect of the disease and/or medications on normal physiologic requirements. A strict definition of “healthy” including meeting BMI criteria and eliminating those taking medications for control of chronic disease risk factors would exclude a majority of the U.S. and Canadian adult populations. The goal is to provide dietary recommendations for the broadest segment of the population.

CURRENT HEALTH STATUS OF THE U.S. AND CANADIAN POPULATIONS

A significant proportion of the U.S. and Canadian populations in certain age groups are at risk of developing chronic diseases during their lifetimes or have already been diagnosed with a chronic disease or with risk factors associated with development of these diseases (Table 3-2). The diseases and risk factors commonly linked to poor dietary intakes include, but are not limited to, cardiovascular disease, hypertension, type 2 diabetes, and some cancers. Increasing rates of overweight and obesity are often contributing factors to these risks and diseases. Children who have a BMI for age at the 95th percentile may not demonstrate clinically relevant disease at a young age but are at risk to be on a trajectory that will put them at higher risk of cardiometabolic risk in the future (Christian Flemming et al., 2020; Delvecchio et al., 2020; Drozdz et al., 2021).

Overall trends in obesity for those 20 years of age and older in the United States, collected through the National Health and Nutrition Examination Survey (NHANES), indicate a steady increase in the prevalence of obesity and severe obesity between the 1999–2000 and 2017–2018 collection cycles (Figure 3-1). During this time period, adults with obesity (BMI greater than or equal to 30) increased from 30.5 to 42.4 percent, while those with severe obesity (BMI greater than or equal to 40) increased from 4.7 to 9.2 percent (Hales et al., 2020; Stierman et al., 2021). Children ages 2 to 19 years also showed dramatic increases in obesity (BMI or Z-score¹) over the same time period (Figure 3-2).

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¹ The Centers for Disease Control and Prevention defines obesity in children as a Z-score > 1.64 and overweight as a Z-score > 1.04 (https://www.cdc.gov/nccdphp/dnpao/growthcharts/resources/modified-z-scores-508.pdf).

TABLE 3-2 Diseases and Risk Factors Commonly Linked to Dietary Intake

In Canada, the most recently reported prevalence of obesity is lower than for the United States at 27 percent for adults and 13 percent for children age 6 to 17 years (Table 3-2). Obesity and overweight are generally associated with an increased risk of all-cause mortality across adult age groups (Twells et al., 2022). As an outcome of unhealthy dietary choices, inadequate access to healthy foods, and lifestyle factors, a large and increasing proportion of the general population is at elevated risk of chronic disease or has been diagnosed with chronic disease risk factors such as hypercholesterolemia, hypertension, or hyperglycemia. Although data on such risks is limited, the issue should not be ignored. Obesity and overweight in childhood and adolescence will likely lead to obesity-related health outcomes in adulthood (USPSTF et al., 2017).

The DRIs are intended for populations that now include a high proportion of individuals with chronic disease risk factors or established diseases that often require medication use. Chronic disease risk factors and the use of medications are common, particularly among middle-aged

and older adults (Table 3-3). Individuals with chronic diseases or chronic disease risk factors should be considered as part of the general population unless there is an effect of the disease and/or medications on nutritional status that would alter normal physiologic requirements. In contrast, persons with existing conditions that clearly are known to alter nutrient metabolism or requirements, or those being treated with medications that alter nutrient metabolism, should not be included in the general population for the DRIs specific to those nutrients.

TABLE 3-3 Use of Medications by Adults with Hypercholesterolemia and Hypertension in the United States and Canada