5.3: A review of Nutrient Reference Values set by the UK, U.S./Canada, European Union, and WHO/FAO (8a.3)

Before reviewing the NRVs established by each of the four indi­vidual authorities, it is stressed again that the process of setting nutrient reference values has evolved from setting a single value, equivalent to the RI, to specifying multiple reference values. In addition to establishing the two core NRVs — the Average Requirement (AR) and Safe Upper Level of Intake (UL) — for a specific nutrient and described in Sections 8a.2.4 and 8a.2.5, other NRVs are often specified and used for multiple purposes, some with a focus on optimizing health and preventing chronic diseases rather than the prevention of nutritional deficiencies. The more important of these other NRVs (the RI, LRI, and AI) are listed in Table 8a.1 and summarized below. The reader is advised to consult Table 8a.1 for a comparison of the recommended terminology with the terms currently used by these four authorities (Lupton et al., 2016).

In addition, the problems of setting NRVs for energy and some macro­nutrients, as well as NRVs for Chronic Disease Prevention, have also been faced by all four authorities. Comments on these difficulties are also considered below.

Nevertheless, many of the principles used previously to define NRVs remain the same (Box 8a.4); see Section 8a.2 for more details.

Box 8a.4: Underlying principles in defining NRVs

• Set for a particular group of indi­viduals with specified characteristics, consuming a specified diet;
• Refer to the average daily need over a reasonable period of time, although the latter has seldom been defined; hence, the suggested amounts do not have to be consumed every day, but omissions or shortfalls must be balanced by increased intake on other occasions;
• Refer to levels of intake needed to maintain health in already healthy indi­viduals; they do not allow for illnesses or stresses in life;
• Based on the typical dietary pattern of the country and may not be appropriate for persons following atypical diets;
• Consider possible interactions that involve nutrients and other dietary components and quantify them, if possible; and
• Assume that require­ments for energy and all the other nutrients are met.

Recommended Intake (RI) (or equivalent) has been established by all authoritative groups. The RI is derived from the AR and its distribution (Figure 8a.6) and is used to assess intakes and plan diets for indi­viduals. Currently, the convention has been to add 2SD to the observed AR to cover the needs of most (i.e., 98%) of indi­viduals of the pop­ula­tion. This means that an indi­vidual whose intake is equal to RI₉₈ (i.e., AR + 2SD of the AR) has a 98% prob­ability that their intake meets their needs (Figure 8a.6).

In the initial harmo­nization initiative in 2005 (King and Garza, 2007) it was suggested that in the future countries might wish to choose a lower percentile level deemed to represent an acceptable risk for nutrient inade­quacy for an indi­vidual in their country instead of the conventional 98% (i.e., RI₉₈). To date, this suggestion has not been adopted.

Lower Reference Intake (LRI) (or equivalent) is also derived from the AR and its distribution and is set at 2 SD below the AR for each nutrient. This reference level represents the lowest intake that will meet the needs of some indi­viduals. It has been established only by the UK and EFSA (Table 8a.1).

Ade­quate Intake (AI) (or equivalent) is applied when there is not enough information to establish an AR for a specific nutrient. The AI is defined as the observed or experimentally derived usual intake by a pop­ula­tion group that appears to sustain health (King and Garza, 2007). The methods used to estimate the AIs vary. For example, for infants < 6mo, AIs are generally based on mean nutrient intakes (except vitamin D) supplied by human milk, whereas for children and adults the AIs can be derived from observed median intakes from national survey data, based on limited experimental data, or in some cases, epidem­iological studies (Trumbo et al., 2013).

In general, mean usual nutrient intakes at the pop­ula­tion level at or above the AI indicate a low prob­ability of inade­quacy. No assumptions can be made, however, about the prevalence of inade­quate intakes when the mean intake of a group falls below the AI. Likewise, if an indi­vidual's usual intake equals or exceeds the AI, the diet is almost certainly ade­quate but again when the usual intake of an indi­vidual falls below the AI, no estimate can be made of the prob­ability of nutrient inade­quacy (IOM, 2000). As noted previously, the Harmonization Committee urged that strenuous efforts should be made to establish an AR for each nutrient so that the inappropriate use of an AI can be avoided.

Energy Requirements are based on the average require­ments (AR) for energy of indi­viduals in a specified sex and life-stage group. The recom­men­dations are not appropriate for the definition of require­ments at the indi­vidual level. Adding an increment equivalent to 2SD to the average energy require­ment would result in a recom­men­dation that exceeds require­ments and lead to overweight and obesity over the long term. Energy require­ments are derived with the assumption that the require­ments for all other nutrients are met (King et al., 2007).

The energy require­ment is defined by FAO/WHO/UNU (2004) as:

“The amount of food energy needed to balance energy expenditure in order to maintain body size, body composition, and a level of physical activity consistent with long-term good health. This includes the energy needed for optimal growth and development of children, for the deposition of tissues during pregnancy, and for the secretion of milk during lactation consistent with the good health of mother and child.”

The criterion chosen on which to base the AR for energy is the total energy expenditure (TEE). When body weight and composition is stable in normal-weight indi­viduals, the energy require­ment is equal to TEE . In the past TEE for some life-stage groups was estimated indirectly by estimating the amount of energy consumed from self-reported food intakes and equating it with the amount of energy expended. This procedure was used by FAO/WHO/UNU (1985) and the United Kingdom (COMA,1991) to set the energy require­ment for young children, but has now been abandoned in view of the concerns about the under­estimation of energy intakes due to under-reporting; see Chapter 7 for more details.

The doubly labeled water method (DLW) method is the most accurate method for measuring TEE in free-living indi­viduals and is now used by several authoritative groups including FAO/WHO/UNU (2004), the U.S. IOM (2005 and the UK SACN (2012); see Chapter 7 for details of the DLW method. TEE measured with DLW method includes the energy used to synthesize growing tissues but does not include the additional energy content of the tissue constituents (basically fat and protein) laid down during normal growth and pregnancy, or the milk produced during lactation.

Appropriate Macronutrient Distribution Range (or equivalent) serves as a guide to the distribution of percentage energy consumed as protein, fat, and carbohydrate said to be consistent with both the maintenance of health and a reduced risk of diet-related chronic disease, while providing ade­quate levels of essential nutrients. Increasingly, recom­men­dations are being made for the contri­bution of free sugars as percentage of energy from total carbohydrate, as well as daily intakes of salt, dietary fiber, fruits and vegetables. (WHO, 2012; WHO, 2015), Although in general the range of intakes set are comparable, their meaning and application differ, with those of the United Kingdom (Section 8a.4.6), EFSA (Section 8a.6.6) and WHO (Section 8a.7.6) being pop­ula­tion mean intake goals, whereas those established by the United States and Canada (Section 8a.5.6) are intended for indi­viduals.

NRVs for Chronic Disease Prevention are being developed by several authoritative groups. However, several challenges have been encountered; these are itemized in Box 8a.5:

Box 8a.5: Challenges in defining NRVs for chronic disease prevention

• Relationships between diet and chronic disease are multifactorial in nature, and dependent on a variety of both nutritional and non-nutritional factors. These may include baseline risk for chronic disease by an indi­vidual, nutrient-diet or nutrient-nutrient interactions, and environmental and other lifestyle factors;
• Chronic diseases develop over a long period making it difficult to accurately measure dietary patterns over such a long period of exposure;
• Published intervention trials are often conducted in selected sub­groups, such as indi­viduals with an already increased risk of disease or history of disease, frequently with intervention dosages that are relatively high and which have relatively short follow-up periods.
• Evidence from observational studies can be compromised by uncertainty arising from problems of confounding, bias, and inaccuracy;
• Use of a validated dietary bio­marker of nutrient exposure requires an estimate of the nutrient intake that corresponds with the clinical out­come;
• Challenges arise with the selection of meaningful and suitable out­come indicators for the chronic disease or an intermediate surrogate bio­marker as a valid predictor of the chronic disease.
• Surrogate bio­markers are often required because the exposure and out­come are separated by such a long time period that clinical signs or symptoms may not be observed for many years. Criteria developed for a qualified surrogate bio­marker are available in IOM (2010).

Adapted from Yaktine and Ross (2019).

A Chronic Disease Risk Reduction (CDRR) has been established for sodium in relation to the benfits of a reduced intake of sodium on cardiovascular disease risk, hypertension risk, systolic blood pressure and diastolic blood pressure. The CDRR for sodium was defined as:

“The intake above which intake reduction is expected to reduce chronic disease risk within an appar­ently healthy pop­ula­tion.” (NASEM, 2019)

For further discussion of these challenges and proposed solutions, see Yetley et al. (2017).