5.5: United States and Canada- Dietary Reference Intakes (8a.5)

The United States and Canada have also adopted a paradigm for nutrient reference values that incorporates data to optimize health, prevent risk of chronic disease, and avoid deficiency. Their approach also provides multiple reference intakes for each nutrient to meet an expanding list of uses. Specifically, the U.S. Food and Nutrition Board has expanded their definition of require­ments to:

• Consider reduction in the risk of chronic degenerative disease, where possible
• Establish an upper level of intake designed to avoid risk of adverse health effects, where data exist
• Include components of food not conven­tionally considered to be essential nutrients (eg choline, carotenoids, lycopenes, boron, vanadium) but which may have a possible benefit to health.

The nutrient reference values were established by a joint committee of both Canadian and U.S. scientists set up by the U.S. Food and Nutrition Board. The Committee adopted the generic term “Dietary Reference Intakes” (DRIs) for a set of reference values for each life-stage and sex group.

The criterion chosen by the U.S. Food and Nutrition Board to define nutrient ade­quacy differs for each nutrient and, sometimes, within the life-stage groups for the same nutrient; details are given in the separate reports published by the Food and Nutrition Board (1997, 1998, 2000, 2001, 2002) for 35 vitamins and minerals. Updated DRIs for calcium and vitamin D are given in IOM (2011).

8a.5.1 U.S. and Canadian Estimated Average Requirement (EAR = AR) for nutrients

This is defined as the median require­ment for a specified criterion of ade­quacy for indi­viduals of a certain life-stage and gender group. The specific criterion selected is defined by a specific function or bio­chem­ical measurement for each nutrient. Values for the EARs for nutrients are available in separate reports of the IOM (1997, 1998, 2000, 2001, 2002). When the mean usual intake of the group is equal to the EAR, 50% of the healthy indi­viduals in that particular life-stage and sex group, meet their require­ment and the other half of the group do not. Hence, usual intake at this level is associated with a 50% risk of inade­quacy (Barr et al.,2003).

As noted earlier (Section 8a.2.4), each EAR refers to the average daily nutrient intake of appar­ently healthy persons over time, and this quantity does not have to be consumed every day. The EAR is especially useful for evaluating the possible ade­quacy of nutrient intakes of pop­ula­tion groups. U.S. and Canadian EARs for elements and vitamins are included in Appendix 8a.3 and Appendix 8a.4 respectively.

8a.5.2 U.S. and Canadian Recommended Daily Allowance (RDA = RI)

This refers to the intake level that meets the daily nutrient require­ments of almost all (≈ 98%) of the indi­viduals in a specific life-stage and sex group. Values are given in the separate reports of the IOM (1997, 1998, 2000, 2001, 2002) (Barr et al., 2003). If the variation in require­ment is well defined and symmetrically distributed, then the RDA is set at two standard deviations above the EAR: intakes at this level have a prob­ability of ade­quacy ≈ 98%

\[\mathrm{RDA}_{98}=\mathrm{EAR}+(2 \mathrm{SD})\nonumber\]

If a coefficient of variation (CV) for the EAR of 10% is assumed, and as CV=SD/EAR, then.

\[\mathrm{RDA}_{98}=\mathrm{EAR}+(0.1 \times \mathrm{EAR})+(0.1 \times \mathrm{EAR})\nonumber\]

Or:

\[\mathrm{RDA}_{98}=1.2 \times \mathrm{EAR}\nonumber\]

Alternatively, if the CV is 15%, then:

\[\mathrm{RDA}_{98}=1.3 \times \mathrm{EAR}\nonumber\]

When the DRIs were first derived, a CV of 12.5% for protein, 15% for copper, molybdenum, and niacin, and 20% for both vitamin A and iodine was applied (King et al., 2007).

No RDA was proposed when there was not enough data to establish an EAR for that nutrient. Because the usual intake at the level of the RDA₉₈ is, by definition, associated with a very low (2–3%) risk of inade­quacy to an indi­vidual, the RDA₉₈ is used as a recom­mended intake when assessing intakes and planning diets for indi­viduals. For example, the appropriate target for phosphorus intake for a woman aged 31–50y is the RDA of 700mg. The RDA should not be used to assess the intakes of groups. RDA values for elements and vitamins are shown in Appendix 8a.3 and Appendix 8a.4 respectively.

8a.5.3 U.S. and Canada: Tolerable Upper Intake Level (UL) for nutrients

The Tolerable Upper Intake level (UL) for nutrients is the highest usual daily nutrient intake level likely to pose no risk of adverse health effects for almost all indi­viduals in a life-stage and sex group. ULs have not been set for some nutrients with limited scientific data. Details of the adverse health effects used to set the ULs are given in the IOM reports (2000, 2001, IOM, 2011).

For some nutrients such as vitamin C, vitamin A, vitamin D, calcium, phosphorus, magnesium, copper, zinc, iron, selenium, iodine, and manganese, the UL refers to the total intake from all sources, including food, fortified food, water, supplements, and medications, where relevant. For others such as niacin and folate, the UL applies to forms from supplements, fortificants, and medications. The UL for magnesium represents intake from pharmacological agents only and does not include intake from food and water. In some cases, the form of the nutrient for the UL differs from that used for the RDA; examples include vitamin E, niacin, and folate.

The UL should be used by health professionals to ensure that nutrient intakes are not too high. As intake increases above the UL, the risk of adverse health effects increases. The UL is based on risk-assessment methodologies similar to those used in toxico­log­ical studies (1998). Figure 8a.1 shows the relationship of the observed level of intake to the risk of inade­quacy and toxicity for the EAR, RDA, and the UL reference values.

8a.5.4. U.S. and Canada Additional Levels

Ade­quate Intake (AI) was also defined by the IOM and refers to a recom­mended average daily nutrient intake level based on observed or experimentally derived approximations or estimates of the nutrient intake by a group (or groups) of appar­ently healthy people. As noted earlier, for infants aged 0–6mo, the AI represents the nutrient intake values (except vitamin D) supplied by human milk (Allen et. al., 2018). The observed or derived intakes are assumed to be ade­quate. The AI is used when there are not enough scientific data to establish an AR (e.g., for fluoride, chromium, manganese, total fiber, and vitamins pantothenate, choline, and biotin), and is used as an intake goal for indi­viduals. If the an indi­vidual's usual intake equals or exceeds the AI, their intake is almost certainly adequate, but if it falls below the AI, no estimate of the prob­ability of nutrient adequacy can be made (IOM, 2000). Recently, AIs have also been set for sodium and potassium (NASEM, 2019).

8a.5.5 U.S. and Canada: Estimated Energy Requirements

Estimated energy require­ments (EER) were compiled by the IOM, and are detailed in IOM (2005). The EER is defined as the average energy intake required to maintain current body weight and physical activity level (PAL) (and to allow for growth or milk production, where relevant) in healthy, normal-weight indi­viduals of a specified age, gender, height, weight, and PAL. Tables provide values as well as equations based on height, weight, sex, age, and level of activity to predict TEE.

The EER values were based on DLW measurements of energy expenditure, and where relevant, the energy content of the tissue constituents (basically fat and protein) laid down in growing infants and children. When body weight and composition is stable in normal-weight indi­viduals, the energy require­ment is equal to total energy expenditure.

Several regression equations were developed for estimating the energy require­ments of different life-stage and gender groups. Separate equations for indi­viduals with a normal body weight (ie BMI 18.5–24.9kg/m²) and those overweight or obese (BMI > 25kg/m²) were developed. An example for the equation for normal-weight men aged 19y and above is given below:

\[\begin{gathered}
\text { EER }=661.8-(9.53 \times \text { Age }[\text { years }]) \\
+\mathrm{PA} \times(15.91 \times \text { Weight }[\mathrm{kg}]+539.6 \times \text { Height }[\mathrm{m}])
\end{gathered}\nonumber\]

Where PA = physical activity coefficient corresponding to a given physical activity level (PAL). Table 8a.4. shows some sample calculations of EER for men with two different BMI values at three different heights and four different physical activity levels (PALs). Sample values for women are also available(Trumbo et al., 2002). More details of the four different physical activity categories are given in Table 8a.5.

Table 8a.4: Estimated energy require­ments (EER) for men of 30y of age¹.
¹ For each year below 30, add 10kcal/d. For each year above 30 subtract 10kcal/d
² PAL = Physical activity level
³ Derived from this regression equation based on doubly labeled water data: EER = 661.8−9.53×Age(y) ×PA×(15.91×Wt(kg)+539.6×Ht(m))
Where:
PA refers to coefficient for Physical Activity Levels (PAL).
PAL = total energy expenditure + basal energy expenditure
PA = 1.0 if PAL ≥ 1.0 < 1.4 (sedentary)
PA = 1.12 if PAL ≥ 1.4 < 1.6 (low active)
PA = 1.27 if PAL ≥ 1.6 < 1.9 (active)
PA = 1.45 if PAL ≥ 1.9 < 2.5 (very active)
Modified from Trumbo et al. (2002).

Height (m)	Weight (kg) for BMI of 18.5 kg/m^2	Weight (kg) for BMI of 24.99 kg/m^2	PAL^2	EER^3 (kcal/d) BMI of 18.5 kg/m^2	EER^3 (kcal/d) BMI of 24.99 kg/m^2
1.50	41.6	56.2	Sedentary Low active Active Very active	1,848 2,009 2,215 2,554	2,080 2,267 2,506 2.898
1.65	50.4	1.50	Sedentary Low active Active Very active	2,068 2,254 2,490 2,880	2,349 2,566 2,842 3,296
1.80	59.9	81.0	Sedentary Low active Active Very active	2,301 2,513 2,782 3,225	2,635 2,884 3,200 3,370

Table 8a.5: Description of physical activity level (PAL) categories. *Walking distance is estimated for the midpoint of the range (i.e., PAL = 1.5 for low active, 1.75 for active, and 2.2 for very active) and for midweight indi­viduals weighing 70kg. Values in parentheses reflect walking distances at the same PAL for relatively heavy weight (120kg) and relatively light weight (44kg) indi­viduals, respectively. Modified from Barr et al., Nutrition Reviews 61: 352–360, 2003.

Physical activity category	PAL (multiples of basal energy expenditure)	Description	Physical Activity Coefficient (PA) M ≥ 19y F ≥ 19y
Sedentary	1.0 to < 1.4	Activities of daily living (ADL) only	1.00 1.00
Low active	≥ 1.4 to < 1.6	ADL plus walking about 2 miles/d (1.5/2.9)* or equivalent	1.11 1.12
Active	≥ 1.6 to < 1.9	ADL plus walking about 7 miles/d (5.3/9.9)* or equivalent	1.25 1.27
Very active	≥ 1.9 to < 2.5	ADL plus walking about 17 miles/d (12.3/22.5)* or equivalent	1.48 1.45

The physical activity coefficients (PAs) for these PAL categories vary slightly among the different regression equations, although the PAL for sedentary indi­viduals is always 1.0 (Barr et al., 2003).

Note for indi­viduals with a BMI ≥ 25, the estimated energy intake required to maintain current weight and activity level is termed the Total Energy Expenditure (TEE) and not the EER. This practice has been adopted because overweight is not consistent with long-term good health (Barr et al., 2003).

8a.5.6. U.S. and Canada Acceptable Macronutrient Distribution Range

The Acceptable Macronutrient Distribution Range (AMDR) of intakes is defined as a range of intakes for a particular energy source associated with reduced risk of chronic disease, while providing ade­quate levels of essential nutrients (IOM, 2002). They are intended for use by indi­viduals, and have been established for carbohydrate, protein, total fat, n-6 poly-unsaturated fatty acids, and α-linolenic acid, as shown in Table 8a.3. Individuals should have intakes that fall within the limits of the AMDRs. If the usual intake of an indi­vidual is below or above the AMDR, there is a potential for increased risk of both inade­quate intakes of essential nutrients and chronic diseases (IOM, 2002). Note that IOM have also defined an EAR and RDA for protein.