Volume 30 Issue 2 Page 176  - June 2005
doi:10.1111/j.1467-3010.2005.00498.x

NEWS AND VIEWS: OFFICIAL DOCUMENTS

US and Canadian Dietary Reference Intakes (DRIs) for the macronutrients, energy and physical activity

B. A. Yon* and R. K. Johnson*

Summary 

The Food and Nutrition Board of the Institute of Medicine (IOM), in conjunction with Health Canada, released the sixth in a series of reports on dietary reference values for the intake of macronutrients and energy by Americans and Canadians. This report established Dietary Reference Intakes (DRIs) for carbohydrate, fibre, fat, fatty acids, cholesterol, protein, amino acids, energy and physical activity. The DRIs replace the USA's Recommended Dietary Allowances (RDAs) last updated in 1989, and Canada's Recommended Nutrient Intakes (RNIs), last published in 1990. A panel of 21 US and Canadian research scientists, clinicians and epidemiologists with expertise in energy, protein and amino acids, carbohydrate, fibre, sugar, lipids, physical activity and life-stage nutrition were appointed to begin the process of reviewing observational and experimental studies published primarily in peer-reviewed journals. The DRIs are based on scientifically grounded relationships between nutrient intake and the prevention of chronic disease, as well as the maintenance of good health. The purpose of this paper is to highlight a number of the definitions, new approaches, and key findings as they apply to the DRIs for the macronutrients, energy and physical activity.

The Dietary Reference Intakes (DRIs) now include four reference values for daily nutrient intake level (IOM 2002). In addition to the RDA, three new reference values include an Estimated Average Requirement (EAR), Adequate Intake (AI), and Tolerable Upper Intake Level (UL).

Recommended Dietary Allowance (RDA): the average daily dietary nutrient intake level sufficient to meet the nutrient requirement of nearly all (97 98%) healthy individuals in a particular life stage and gender group

Adequate Intake (AI): the recommended average daily intake level based on observed or experimentally determined approximations or estimates of nutrient intake by a group (or groups) of apparently healthy people that are assumed to be adequate used when an RDA cannot be determined

Tolerable Upper Intake Level (UL): the highest average daily nutrient intake level that is likely to pose no risk of adverse health effects to almost all individuals in the general population. As intake increases above the UL, the potential risk of adverse effects may increase

Estimated Average Requirement (EAR): the average daily nutrient intake level estimated to meet the requirement of half the healthy individuals in a particular life stage and gender group

In the case of energy, an Estimated Energy Requirement (EER) is provided; it is the average dietary energy intake that is predicted to maintain energy balance in a healthy adult of a defined age, gender, weight, height and level of physical activity, consistent with good health. In children, pregnant and lactating women, the EER is taken to include the needs associated with the deposition of tissues or the secretion of milk at rates consistent with good health.

Reprinted with permission from Dietary Reference Intakes for Energy. Carbohydrate, Fibre, Fat, Fatty Acids, Cholesterol, Protein and Amino Acids (Macronutrients) © (2002) by the National Academy of Sciences, courtesy of the National Academies Press, Washington DC.

In addition to the RDA, the nutrient intake level sufficient to meet the needs of the majority of people, most nutrients now have an EAR which establishes the average daily nutrient intake estimated to meet the requirement of half of the people in a particular life stage or gender group. When an EAR for a nutrient cannot be determined, an AI is set, based on observed or experimentally determined estimates. Lastly, most nutrients also have a UL which is the highest daily nutrient intake likely to pose no risk to health. Transitioning from the earlier RDAs and RNIs to using the new DRIs will take time on the part of health professionals. Guidance in the use of each of the reference values has been provided when assessing and planning diets and nutrient intakes for both individuals and groups (Table 1).

The primary role of carbohydrates (sugars and starches) is to provide energy to the cells of the body, particularly the brain that is carbohydrate dependent. For the first time a RDA for carbohydrate was set at 130 g/day for adults and children, based on the brain's average utilisation of glucose. Pregnant and lactating women have higher RDAs set at 175 and 210 g/day, respectively.

While fat is a major source of energy and aids in the absorption of fat-soluble vitamins and nutrients, no EAR, AI, nor UL was determined because the level of fat intake at which risk for chronic disease begins is very low. Such a low intake of fat cannot be achieved while maintaining adequate nutrient intake. For this reason it was recommended that saturated fat, trans fatty acids and dietary cholesterol intake be kept as low as possible while consuming a nutritionally adequate diet. An AI was determined for the essential n-6 polyunsaturated fatty acid, linoleic acid, at 17 and 12 g/day for men and women respectively. Because deficiencies in linoleic acid are non-existent in the US, this level was determined based on median intakes. An AI for the n-3 polyunsaturated fatty acid, -linolenic acid, was also established at 1.6 and 1.1 g/day for men and women, respectively, again based on median intakes in the US.

The RDA for adults for protein remained at 0.8 g/kg body weight/day. Pregnant and lactating women have higher needs due to tissue deposition and milk production. Their RDA was set at 1.1 g/kg body weight/day or an additional 25 g/day. For the first time, age based recommended intakes for all nine of the indispensable essential amino acids were established. A scoring pattern was developed which can be used to evaluate the quality of protein sources such as milk, wheat or kidney beans, by the relative amount of amino acids.

Three new definitions of fibre were developed to establish uniformity for nutrition labelling and set standards as new fibre sources are developed. Dietary Fibre was defined as non-digestible carbohydrates and lignins that are intrinsic and intact in plants. Functional Fibre was defined as isolated, non-digestible carbohydrates that have beneficial physiological effects in humans. Total Fibre is the sum of Dietary Fibre and Functional Fibre. While not an essential nutrient, the primary beneficial effects of fibre include laxation, satiety, which contributes to weight control, attenuation of blood glucose levels and normalisation of serum cholesterol. The best approach for expressing fibre requirements is based on the amount of food consumed (g/kcal). However, since many people do not know how many kcals they consume daily, the AI was based instead on usual daily energy intake and expressed in g/day. The AI for Total Fibre in foods was set at 38 and 25 g/day for men and women, respectively, based on a suggested intake of 14 g/1000 kcal. Those individuals who consume significantly more or less energy than the reference intakes for their age should consider adjusting their total fibre intake accordingly.

 Acceptable macronutrient distribution ranges

What combination and proportion of energy sources are most beneficial to health and longevity? The scientific data does not support specific recommendations; but rather indicate trends between intake (particularly fat and carbohydrate) and disease. Based on this evidence suggesting a role in chronic disease, as well as to ensure sufficient intake of essential nutrients, Acceptable Macronutrient Distribution Ranges (AMDR) were established for children and adults (Table 2). The AMDR are expressed as a percent of total energy and include an upper and lower boundary. If a person consumes above or below this range, there is the potential for increasing the risk of certain chronic diseases (obesity, Type-2 diabetes, coronary heart disease, etc.), or subsequent insufficient intake of essential nutrients. The AMDR for total fat is not less than 20% of total energy intake to prevent a decrease in high-density lipoprotein (HDL) associated with very low fat diets. Similarly, in order to prevent high intakes of fat associated with increased risk of coronary heart disease and possible weight gain, the AMDR for carbohydrate is not less than 45% of total energy intake. This lower boundary for carbohydrate also helps to ensure adequate fibre intake. Studies indicate a relationship between higher intakes of added sugars (from production and processing) and lower intakes of essential micronutrients. The major sources of added sugars (soft drinks, fruit drinks, cookies, cakes, etc.) are often energy dense and nutrient poor, and displace more nutritious foods from the diet. Foods containing naturally occurring sugars include fruits and dairy products, which in turn are nutrient dense. It was suggested that added sugars should not exceed 25% of total calories. Protein's upper boundary of 35% was set to ensure adequate intake of the other energy nutrients.

Recognising that maintaining a healthy weight is dependent upon balancing total energy consumption with energy expenditure, the DRIs established new EERs for infants, children, men and women, including pregnant and lactating women. EER is defined as the dietary energy intake that predicts the maintenance of energy balance in healthy, normal weight individuals of a defined age, gender, weight, height and physical activity level (PAL). The EER formulas are based on prediction equations from a database including total energy expenditure (TEE) measurements of over 1600 free-living men, women and children of all ages and body compositions from around the world. These TEE measurements used doubly labelled water (DLW) which provides a closer approximation to actual energy expenditure than the past practice of basing energy recommendations on factorial methods or self-reported dietary intakes.

The specific prediction equations for determining EER for normal weight children and adults are shown in Table 3. For infants and children, EER is determined as TEE plus the energy required for supporting growth. Similarly, EER for pregnant and lactating women include TEE and the calorie requirements for tissue deposition during pregnancy and milk production during lactation. As EER values are intended for the maintenance of body weight within a range for good health, these equations are not used for the overweight and obese. Rather TEE equations estimate energy requirements for weight maintenance for children aged 3 to 18 years with a body mass index (BMI) > 85th percentile and adults with a BMI =" type="#_x0000_t75">  25 kg/m².

Physical activity is the most variable component when determining EER. Each of the EER equations include a physical activity coefficient value which corresponds to one of four PALs: sedentary, low active, active and very active. PAL is described as the ratio of total to basal daily energy expenditure. A sedentary PAL (1.0 1.39) takes into account the energy expended in activities during the course of normal daily living. Walking equivalencies, based on body weight, can be used to estimate energy expended above sedentary and subsequent PAL (Table 4). An adult weighing 70 kg, walking 2, 7 or 17 miles per day (at 3 4 miles/h), would expend enough additional energy above sedentary to correspond to the low-active, active, and very active categories. A heavy-weight person would not have to walk as many miles as a light-weight person in order to reach each higher PAL because the energy required for weight-bearing activities is approximately proportional to body weight.

Energy intake above EER would clearly result in weight gain and for this reason a UL does not apply to energy. If a person does not maintain his or her weight at their calculated EER, then the PAL may need to be adjusted.

How active is active?

In order to promote weight maintenance and accrue the health benefits of physical activity, which include overall well being, enhanced quality of life and lower mortality rates, 60 min of daily moderate physical activity is recommended. This level of physical activity corresponds to the active lifestyle as defined by PAL. While similar to Canada's Physical Activity Guide (Health Canada 1998), it is higher than the 30 min, most days of the week, previously recommended by the US Surgeon General's Report (DHHS 1996). However, the newly released 2005 Dietary Guidelines for Americans now concur with IOM's recommendation of 60 min of moderate to vigorous physical activity, most days of the week, in order to achieve and maintain a healthy body weight (DHHS & USDA 2005). The 2005 Dietary Guidelines also recommend 60 90 min of daily moderate physical activity for previously overweight adults to sustain weight loss. Physical activity is cumulative and includes normal daily activities such as taking the stairs and light housekeeping or gardening, in addition to moderate to vigorous exercise such as walking or running.

Conclusion

The DRIs establish new categories of reference values when assessing and planning diets for both individuals and groups. Acceptable Macronutrient Distribution Ranges illustrate that a healthy diet can be achieved with a wide range of macronutrients. The prediction equations for EER, based for the first time on doubly labelled water studies, are an improvement over factorial equations. Building in a variable for PALs further enhances their accuracy. People of small stature may find it difficult to meet basic micronutrient needs based on their EER. In order to increase their EER and consume more food to meet their nutrient needs, they will need to be more physically active. Physical activity recommendations have been increased for adults to promote healthy weight and the prevention of chronic disease.

The full text of the Dietary Reference Intakes for energy, carbohydrate, fibre, fat, fatty acids, cholesterol, protein and amino acids is available online at http://www.nap.edu

Affiliations

*Department of Nutrition and Food Sciences, University of Vermont, Burlington, VT, USA

Correspondence

Rachel K. Johnson, PhD, MPH, RD, Professor of Nutrition, 108 Morrill Hall, CALS Dean's Office, University of Vermont, Burlington, VT 05405, USA.
E-mail: rachel.johnson@uvm.edu

Table 1 Uses of dietary reference intakes for healthy individuals and groups 

Table 2 Acceptable macronutrient distribution ranges

Table 3 Estimated Energy Expenditure* prediction equations at four physical activity levels

Table 4 Physical act, ivity le, vel categories , and walking equivalence*

To cite this article
Yon, B. A. & Johnson, R. K. (2005)
US and Canadian Dietary Reference Intakes (DRIs) for the macronutrients, energy and physical activity.
Nutrition Bulletin 30 (2), 176-181.
doi: 10.1111/
j.1467-3010.2005.00498.x