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National Research Council (US) Subcommittee on the Tenth Edition of the Recommended Dietary Allowances. Recommended Dietary Allowances: 10th Edition. Washington (DC): National Academies Press (US); 1989.

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Recommended Dietary Allowances: 10th Edition.

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The energy requirement of an individual has been defined by a recent international working group as:

that level of energy intake from food which will balance energy expenditure when the individual has a body size and composition, and level of physical activity, consistent with long-term good health; and which will allow for the maintenance of economically necessary and socially desirable physical activity. In children and pregnant or lactating women the energy requirement includes the energy needs associated with the deposition of tissues or secretion of milk at rates consistent with good health (WHO, 1985).

For groups, recommended energy allowances represent the average needs of individuals. In contrast, recommended allowances for other nutrients are high enough to meet an upper level of requirement variability among individuals within the groups.

If energy intake is consistently above or below a person's requirement, a change in body energy stores can be expected. If the imbalance between intake and expenditure continues over long periods, changes in body weight or body composition will occur and may adversely affect health (see DHHS, 1988; NRC, 1989).

Recommended energy allowances are stipulated as kilocalories (kcal) per day a of physiologically available energy (i.e., the amount of potential food energy that can be absorbed and utilized). Most food composition tables list physiologically available energy values based on digestibility trials of specific foods conducted by Atwater (Merrill and Watt, 1955). These specific energy values have been confirmed by others (Bernstein et al., 1955; Southgate and Durnin, 1970). The conventional general energy conversion factors of 4 kcal/ g of food protein or food carbohydrate and 9 kcal/g of food fat (also derived by Atwater) are adequate for computation of the energy content of typical diets in the United States, but not of specific foods nor of diets based heavily on fibrous plant foods. Alcohol (ethanol) has a caloric value of 7 kcal/g, or 5.6 kcal/ml.


Total energy expenditure includes the energy expended at rest, in physical activity, and as a result of thermogenesis. These components, in turn, are affected by several variables, including age, sex, body size and composition, genetic factors, energy intake, physiologic state (e.g., growth, pregnancy, lactation), coexisting pathological conditions, and ambient temperature.

Resting Energy Expenditure

Unless levels of physical activity are very high, resting energy expenditure (REE) is the largest component of total energy expenditure. REE represents the energy expended by a person at rest under conditions of thermal neutrality. Basal metabolic rate (BMR) is more precisely defined as the REE measured soon after awakening in the morning, at least 12 hours after the last meal. REE is not usually measured under basal conditions. REE may include the residual thermic effect of a previous meal and may be lower than BMR during quiet sleep. In practice, BMR and REE differ by less than 10%, and the terms are used interchangeably.

REE is closely correlated with measures of lean body mass. In individuals of similar age, sex, height, and weight, differences in lean body mass account for approximately 80% of the variance in measured REE. Differences in lean body mass also account for most of the observed difference in REE between men and women, and between younger and older adults of similar heights and weights.

REE is commonly estimated by using any of several empirically derived equations. The values used in this volume were derived from equations published by WHO (1985) b (Table 3-1). These calculated values are not completely accurate for individuals, but can serve as a guide for dietary planning. These equations take into account age, sex, and weight, but ignore height, which was found not to affect the precision of prediction appreciably.

TABLE 3-1. Equations for Predicting Resting Energy Expenditure from Body Weight.


Equations for Predicting Resting Energy Expenditure from Body Weight.

Physical Activity

For most people, the second largest component of total energy expenditure is the energy expended in physical activity. In the past, estimates of energy requirements were based in part on the different physical activity levels associated with different occupations. With the introduction of labor-saving machinery, occupational energy expenditures and differences between occupations tended to decline. Renewed emphasis on physical fitness has led some people, but not all, to increase recreational activity, such as walking, jogging, and sports, resulting in greater variability in the discretionary component of energy expenditure. Thus, the traditional estimation of energy needs according to occupation is no longer adequate.

For schoolchildren and people in sedentary occupations, long-term well-being may depend on increasing physical activity during leisure time. Indeed, for many Americans, increasing energy expenditure through activity may be a more effective way of maintaining health, including desirable body weight, than reduction in energy intake. Increased activity promotes fitness and allows a more generous intake of food, which makes for easier attainment of RDA levels of nutrients.

The energy costs of many different types of work and activity have been measured (Durnin and Passmore, 1967; WHO, 1985 c ). Representative values are given in Table 3-2, expressed as multiples of resting energy expenditure. Activities are aggregated according to intensity of effort, such as resting, very light, light, moderate, and heavy activity.

TABLE 3-2. Approximate Energy Expenditure for Various Activities in Relation to Resting Needs for Males and Females of Average Size.


Approximate Energy Expenditure for Various Activities in Relation to Resting Needs for Males and Females of Average Size.

Energy requirement can be estimated, albeit imprecisely, if the typical activity pattern is known. An average daily “activity factor” can be calculated using the values in Table 3-2 for different activities, weighted by the time engaged in such activities. The weighted activity factor is multiplied by the REE (calculated from the equations in Table 3-1, or measured) to derive energy requirement. An example is shown in Table 3-3, in which energy expenditures of young adults on unusually inactive and active days are compared. Estimated requirements for the inactive days are 1,500 and 1,200 kcal/day less for males and females, respectively, than for the active days in the example. A valid estimate of energy requirement would need to take into account activity over a sufficiently long time (weekdays, weekends, season) to be representative.

TABLE 3-3. Example of Calculation of Estimated Daily Energy Allowances for Exceptionally Active and Inactive 23-Year-Old Adults.


Example of Calculation of Estimated Daily Energy Allowances for Exceptionally Active and Inactive 23-Year-Old Adults.

A very sedentary person who habitually spends many hours a day either lying or sitting is unlikely to expend the same amount of energy at rest and for a given task as one who habitually undertakes more strenuous activity several hours a day. A habitually sedentary person would almost certainly have less muscle mass and might lack the physique to perform heavy physical work efficiently (Garrow and Blaza, 1989). Thus, differences in energy requirement are due both to pattern of activity and the body composition that results from that pattern of activity.

Activity factors associated with a range of activity patterns are listed in Table 3-4. These factors are similar to those specified by WHO (1985) and may be used as a rough guide to requirements if the proportion of time spent in different activities is unknown. Patterns typical of the U.S. population are in the categories light (1.5–1.6 × REE) or moderate (1.6–1.7 × REE). The activity factor of 1.3 × REE is a minimum value, reflecting 10 hours a day at rest and 14 hours of very light activity. This level may be lower than is compatible with desirable cardiovascular fitness (WHO, 1985).

TABLE 3-4. Factors for Estimating Daily Energy Allowances at Various Levels of Physical Activity for Men and Women (Ages 19 to 50).


Factors for Estimating Daily Energy Allowances at Various Levels of Physical Activity for Men and Women (Ages 19 to 50).

Metabolic Response to Food

Metabolic rate increases after eating, reflecting the size and composition of the meal. It reaches a maximum approximately 1 hour after the meal is consumed and virtually disappears 4 hours afterward (Garrow, 1978). In relation to total energy expenditure, the thermic effect of meals is relatively small—on the order of 5 to 10% of energy ingested. Small differences in this component of energy expenditure could have significant cumulative long-term effects, but are generally undetectable, being lost in the day-to-day variation in energy metabolism.


REE varies with the amount and composition of metabolically active tissue, which varies with age. The lean body mass of infants and young children contains a greater proportion of metabolically active organs than in adults. In adults, skeletal muscle, which has a lower rate of resting metabolism, is a major component of the lean body mass. Lean body mass declines beyond early adulthood at a rate of about 2 to 3% per decade, and the REE declines proportionately. Differences in body composition among age groups are reflected in the age-specific equations for calculating REE.

Activity patterns also vary with age. Unless constrained by the environment, children typically are active (1.7 to 2.0 × REE). Both physiological and social changes affect energy expenditure patterns of older adults. In the longitudinal study of aging conducted in Baltimore, Maryland, McGandy et al. (1966) found the activity component to be affected more than the REE over time and an especially sharp drop in activity after age 75. Elmstahl (1987) measured energy expenditure of very elderly institutionalized people (average age, 83 years) who had a variety of chronic conditions but were still able to participate in physical activity. The average energy expenditure of men and women was similar—1.45 to 1.50 × measured REE. Under laboratory conditions of controlled activity (sedentary, except for 0.5 hour cycling per day), the average expenditure of 68-year-old men was 1.58 × REE (Calloway and Zanni, 1980).


Differences in body composition of boys and girls occur as early as the first few months of life but are relatively small until children reach approximately 10 years of age. Thereafter, the differences in body composition become greater throughout adolescence. After maturity, men have proportionately greater muscle mass than do women, who have a greater proportion of body weight as fat. In adults, REE per unit of total body weight differs by approximately 10% between sexes. In the past, because of occupational differences, men and women often had markedly different energy expenditures, but their occupational activity requirements now are similar.


The cost of growth includes energy deposited as protein and fat plus the cost of their synthesis. The average energy cost is about 5 kcal/g of growth tissue gained (Roberts and Young, 1988). Except during the first year of life, growth is a very small (approximately 1%) component of total energy requirement.

Body Size

Persons with large (or small) bodies require proportionately more (or less) energy per unit of time for activities (e.g., walking) that involve moving mass over distance. Their total REE also will be higher (or lower) than the average for persons of the same sex and age. Energy allowances must be adjusted for the variation in requirements that result from these differences in body size. Adjustment will need to be greater for persons who are both large and active.

Weight may be used as a basis for adjusting energy allowances for different body sizes, provided the individuals are not appreciably over or under median weights for height within a given age and sex category (see Table 2-1 in Chapter 2). For obese or undernourished people, energy allowances should be adjusted according to the normal weight for their height.


In the United States, the ambient temperature of most living environments lies in the comfortable range of 20°C to 25°C (68°F to 77°F). Most people are protected against cold by warm clothes and heated environments. The effects of high temperatures are also minimized since many people also live and work in air-conditioned buildings. Not everyone is insulated from environmental exposure, however. When there is prolonged exposure to cold or heat, energy allowances may need adjustment.

The energy cost of work is slightly greater (approximately 5%) in a mean temperature below 14°C than in a warm environment (Johnson, 1963). A relatively small increase in energy expenditure (2% to 5%) is associated with carrying the extra weight of cold-weather clothing and footwear. Such clothing also increases energy expenditure by its so-called hobbling effect. If exposure to cold air or water leads to body cooling, energy needs will increase because of the increased metabolic rate associated with shivering and other muscle activity.

Energy requirements are also increased in people performing heavy work at a high temperature—37°C (99°F) or higher. Under such conditions, body temperature and metabolic rate increase, and extra energy is expended to maintain thermal balance (Johnson, 1963). Whereas little adjustment is necessary in environmental temperatures between 20°C and 30°C (68°F–86°F), energy allowances may need to be slightly increased wherever persons are required to be physically active in extreme heat.

With the above exceptions, no adjustment in energy allowance appears to be needed to compensate for change in climate, apart from climatic effects on physical activity patterns.



In Table 3-5, recommended energy allowances for reference adults engaged in light to moderate activity are given for three age categories: 19 to 24 years, 25 to 50, and over age 50. Weights and heights of young adults between 19 and 24 years of age are close to those of mature adults; although some persons within this age group may still be growing, the very small energy need for growth is well within population variability. The recommended allowances should be adjusted to account for increased physical activity and for larger or smaller body size, but rarely for climate.

TABLE 3-5. Median Heights and Weights and Recommended Energy Intake.


Median Heights and Weights and Recommended Energy Intake.

The recommended allowances for adults with a light-to-moderate activity level were calculated by using the WHO (1985) equations for the calculation of REE (Table 3-1) and multiplying the results by an activity factor. For men, the activity factor 1.67 × REE was used for the 19- to 24-year age group and 1.60 for those ages 25 to 50; for women, 1.60 and 1.55 were used for the respective age periods. These values are a blend of light and moderate classes of activity as suggested by WHO. For men of reference body size, the average allowance is 2,900 kcal/day; for women, it is 2,200 kcal. With light-to-moderate activity, the coefficient of variation in energy requirements of adults is approximately 20% (Garrow, 1978; McGandy et al., 1966; Todd et al., 1983). This range reflects variability in both the REE and the activity factor among the individuals in the group. This range does not cover the needs of persons with heavy activity patterns, for whom allowances should be adjusted to 2.0 × REE or higher.

The energy allowance for persons beyond age 50 is 1.5 × REE. This assumes continued light-to-moderate activity, which should be encouraged in the interest of maintaining muscle mass and well-being. It should not be assumed that the marked decline in activity often observed in the elderly is either inevitable or desirable. The average allowance for men of reference size (77 kg) is 2,300 kcal/day; for women, it is 1,900 kcal/day. A normal variation of ±20% is accepted as for younger adults. The requirements of persons beyond age 75 are likely to be somewhat less as a result of reduced body size, REE, and activity.


Pregnancy imposes additional energy needs because of added maternal tissues and growth of the fetus and placenta. For a full-term pregnancy, during which the mother has gained 12.5 kg and has given birth to a 3.3-kg baby, total energy cost has been estimated to be 80,000 kcal (Hytten and Leitch, 1971). This estimate has been used in considering energy allowances for pregnancy (WHO, 1985). Alternative assumptions concerning the composition of tissue gained, observations of energy intake by pregnant women, and measurement of resting metabolism have led to estimates as low as 45,000 kcal (Durnin, 1986) and 68,000 kcal (van Raaij, 1989) to as high as 110,000 kcal (Forsum et al., 1988) as the cost of pregnancy in healthy, well-nourished women.

Epidemiological evidence suggests that adequate maternal weight gain, including some maternal fat storage, is needed to ensure that the size of the newborn is optimal for survival. Thus, storage of energy is included as part of the energy requirement of pregnancy.

Metabolic requirements and physical activity may change during pregnancy, but there are no well-documented studies providing the data from which to estimate changes in energy allowance for these two factors.

WHO (1985) estimated the energy allowance for pregnant women by dividing the gross energy cost (80,000 kcal) by the approximate duration of pregnancy (250 days following the first month), yielding an average value (after rounding) of 300 kcal/day for the entire pregnancy. The present subcommittee accepts this calculation with the caution that any diminution in activity with advancing pregnancy must be taken into account. Unless the woman begins pregnancy with depleted body reserves, additional energy intake is probably not required during the first trimester. An additional 300 kcal/day is recommended during the second and third trimesters.


Energy requirements for lactation are proportional to the quantity of milk produced. The average energy content of human milk from well-nourished mothers is about 70 kcal/100 ml (WHO, 1985). The efficiency with which maternal energy is converted to milk energy is assumed to be approximately 80% (range, 76 to 94%) (Sadurkis et al., 1988; Thomson et al., 1970; WHO, 1985). Thus, approximately 85 kcal are required for every 100 ml of milk produced. Average milk secretion during the first 6 months of lactation is 750 ml/day; in the second 6 months, it is 600 ml/day. The coefficient of variation is 12.5%. Thus, the average woman would require an additional 640 kcal and 510 kcal/day in the first and second 6 months, respectively. The upper boundary of requirements (+ 2 SD) would be 800 and 640 kcal.

Energy allowances during lactation may be partially met by extra fat stored during pregnancy. Such energy reserves, about 2 to 3 kg in women who gain 11 to 12 kg during pregnancy, normally are utilized during the first few months of breastfeeding. These fat stores can theoretically provide about 100 to 150 kcal/day during a 6-month lactation period. Accordingly, an additional average allowance of 500 kcal/day is recommended throughout lactation, which, assuming appropriate weight gain during pregnancy, may permit readjustment of maternal body fat stores upon termination of breastfeeding. The recommended allowance for women whose gestational weight gain is subnormal, or whose weight during lactation falls below the standard for their height and age, is an additional 650 kcal/day during the first 6 months.

Infants, Children, and Adolescents

For children less than 10 years of age, the energy requirement is estimated from intake associated with normal growth. Data on energy intakes recorded in studies of children in the United States, Canada, the United Kingdom, and Sweden have been compiled by WHO (1985). The international groups accepted the actual requirement to be 5% greater than these reported intakes, allowing for the likelihood that intake was underestimated.

The requirement figures of 108 kcal and 98 kcal/kg for infants from birth through 6 months and 6 months through 12 months, respectively, were estimated by WHO from intakes of healthy infants from developed countries. These figures are about 15% higher than recent estimates derived from energy expenditure measurements, using deuterium oxide methodology, with an allowance for the theoretical amount of energy deposited as tissue added in growth (Prentice et al., 1988). The new estimates, 95 kcal and 84 kcal/kg at the respective age periods, based on expenditure plus storage, can be taken as equal to dietary requirement if the metabolizable energy value of foods consumed (human milk, formula, beikost) is estimated correctly. Growth velocity is slower than the NCHS 50th centile in infants in these recent (1984–1988) studies and skinfold thickness is less than the Tanner standards developed in the 1950s (Tanner, 1984), indicating that infants are now leaner. There is, at present, insufficient evidence from which to judge whether or not this secular trend is desirable. Recognizing that infants self-regulate intake and that questions remain unanswered (including the question of metabolizable energy values), the subcommittee has elected to accept the WHO figures.

From birth through age 10 years, no distinction in energy requirement is made between sexes. Above age 10, separate allowances are recommended for boys and girls because of differences in the age of onset of puberty and evolving activity patterns. There is great variability in both the timing and magnitude of the adolescent growth spurt. Activity patterns are also quite variable. Thus, recommendations for these groups assume a wider range within which energy allowances can be adjusted individually to take account of body weight, activity, and rate of growth.

The recommended energy allowances from birth through age 10 years shown in Table 3-5 are those of the international agencies (WHO, 1985). Allowances for other age groups are adjusted to reflect typical activity patterns in the United States. Those for older girls and boys are based on a predicted activity factor of 1.7 at 11 years of age and a decrease to the adult light to moderate activity value of 1.6 by age 15 in girls and age 19 in boys.


Energy intakes of children as reported in both the 1977–1978 Nationwide Food Consumption Survey (USDA, 1984) and the 1976– 1980 second National Health and Nutrition Examination Survey (NCHS, 1979) coincide with the allowances proposed for these age groups. From early adolescence onward in women and in men a few years later, reported average intakes are substantially below the RDA. Data from the 1986 Continuing Survey of Food Intakes by Individuals (USDA, 1988) indicate that mothers consume an average of 1,473 kcal/day, the same amount of energy as their children ages 1 to 5 years. It is commonly believed that adults underestimate food intake and that alcohol consumption in particular is underreported (NRC, 1986). If the underreported items are seasonings or adjuvants with low levels of essential nutrients (e.g., fats and oils, sweeteners) or alcoholic beverages, only energy intake will be affected seriously.


Reference weights in the present edition differ from those in the ninth. Thus, the allowances expressed as kcal/day are not directly comparable with values in the previous edition. Nevertheless, the changes made in adult allowances are generally small despite the different method used to derive the estimated allowances. The allowances for infants and children 7 to 10 years old are lower than in previous editions because of the new information on observed intakes of children in developed countries. For other ages, new allowances expressed per kilogram of body weight are trivially higher or lower than previously.


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One kilocalorie is the amount of heat necessary to raise 1 kg of water from 15°C to 16°C. The accepted international unit of energy is the joule (J). To convert energy allowances from kilocalories to kilojoules (kJ), a factor of 4.2 may be used (1 kcal equals exactly 4.184 kJ). Because the energy content of diets is usually greater than 1,000 kJ, the preferred unit is the megajoule (MJ), which is 1,000 kJ.


The WHO (1985) report contains extensive references to the original investigations. The reader is referred to that report for full documentation.


In the United States, many investigators use the equations of Harris and Benedict (1919) to determine BMR. The values calculated from these equations do not differ significantly from those derived from the international equations used in this volume.

Copyright © 1989 by the National Academy of Sciences.
Bookshelf ID: NBK234938


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