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TABLE 1 Equations to Estimate Energy Requirement Infants and Young Children Estimated Energy Requirement (kcal/day) = Total Energy Expenditure + Energy Deposition EERa = (89 ¥ weight [kg] –100) + 175 0–3 months EER = (89 ¥ weight [kg] –100) + 56 4–6 months EER = (89 ¥ weight [kg] –100) + 22 7–12 months EER = (89 ¥ weight [kg] –100) + 20 13–35 months Children and Adolescents 3–18 years Estimated Energy Requirement (kcal/day) = Total Energy Expenditure + Energy Deposition Boys EER = 88.5 – (61.9 ¥ age [y]) + PAb ¥ [(26.7 ¥ weight [kg]) + (903 ¥ height [m])] + 20 3–8 years EER = 88.5 – (61.9 ¥ age [y]) + PA ¥ [(26.7 ¥ weight [kg]) + (903 ¥ height [m])] + 25 9–18 years Girls EER = 135.3 – (30.8 ¥ age [y]) + PA ¥ [(10.0 ¥ weight [kg]) + (934 ¥ height [m])] + 20 3–8 years EER = 135.3 – (30.8 ¥ age [y]) + PA ¥ [(10.0 ¥ weight [kg]) + (934 ¥ height [m])] + 25 9–18 years Adults 19 years and older Estimated Energy Requirement (kcal/day) = Total Energy Expenditure EER = 662 – (9.53 ¥ age [y]) + PA ¥ [(15.91 ¥ weight [kg]) + (539.6 ¥ height [m])] Men EER = 354 – (6.91 ¥ age [y]) + PA ¥ [(9.36 ¥ weight [kg]) + (726 ¥ height [m])] Women Pregnancy Estimated Energy Requirement (kcal/day) = Nonpregnant EER + Pregnancy Energy Deposition 1st trimester EER = Nonpregnant EER + 0 2nd trimester EER = Nonpregnant EER + 340 3rd trimester EER = Nonpregnant EER + 452 Lactation Estimated Energy Requirement (kcal/day) = Nonpregnant EER + Milk Energy Output – Weight Loss 0–6 months postpartum EER = Nonpregnant EER + 500 – 170 7–12 months postpartum EER = Nonpregnant EER + 400 – 0 NOTE: These equations provide an estimate of energy requirement. Relative body weight (i.e., loss, stable, gain) is the preferred indicator of energy adequacy. a EER = Estimated Energy Requirement. b PA = Physical Activity Coefficient (see Table 2).

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PART II: ENERGY 83 ENERGY E nergy is required to sustain the body’s various functions, including res- piration, circulation, physical work, metabolism, and protein synthesis. This energy is supplied by carbohydrates, proteins, fats, and alcohol in the diet. A person’s energy balance depends on his or her dietary energy intake and energy expenditure. Numerous factors affect energy expenditure and re- quirements, including age, body composition, gender, and physical activity level. An imbalance between energy intake and expenditure results in the gain or loss of body components, mainly in the form of fat, and determines changes in body weight. The Estimated Energy Requirement (EER) is defined as the average dietary energy intake that is predicted to maintain energy balance in a healthy adult of a defined age, gender, weight, height, and a level of physical activity that is consistent with good health. A person’s body weight is a readily monitored indicator of the adequacy or inadequacy of habitual energy intake. To calculate the EER, prediction equations for normal-weight individuals (body mass index [BMI] of 18.5 kg/m2 up to 25 kg/m2) were developed using data on total daily energy expenditure as measured by the doubly labeled water (DLW) technique. Equations can be found in Table 1. In children and in preg- nant and lactating women, the EER accounts for the needs associated with growth, deposition of tissues, and the secretion of milk at rates that are consis- tent with good health. The EER does not represent the exact dietary energy intake needed to maintain energy balance for a specific individual; instead it reflects the average needs for those with specified characteristics. Although EERs can be estimated for four levels of activity from the equa- tions provided in Table 2, the active Physical Activity Level (PAL) is recom- mended to maintain health. Thus, energy requirements are defined as the amounts of energy that need to be consumed by an individual to sustain a stable body weight in the range desired for good health (BMI of 18.5 kg/m2 up to 25 kg/m2), while maintaining a lifestyle that includes adequate levels of physi- cal activity. There is no Recommended Dietary Allowance (RDA) for energy because energy intakes above the EER would be expected to result in weight gain. Simi- larly, the Tolerable Upper Intake Level (UL) concept does not apply to energy because any intake above a person’s energy requirement would lead to weight gain and likely increased risk of morbidity.

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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 84 TABLE 2 Physical Activity Coefficients (PA Values) for Use in EER Equations Sedentary Low Active Active Very Active (PALa 1.0–1.39) (PAL 1.4–1.59) (PAL 1.6–1.89) (PAL 1.9–2.5) Typical daily living activities PLUS at least 60 minutes Typical daily living of daily moderate activities activity PLUS Typical daily living PLUS Typical daily living 30–60 minutes activities an additional 60 activities (e.g., of daily moderate PLUS minutes of vigorous household tasks, activity at least 60 activity or 120 walking to the (e.g., walking at minutes of daily minutes of moderate bus) 5–7 km/h) moderate activity activity Boys 3–18 y 1.00 1.13 1.26 1.42 Girls 3–18 y 1.00 1.16 1.31 1.56 Men 19 y + 1.00 1.11 1.25 1.48 Women 19 y + 1.00 1.12 1.27 1.45 a PAL = Physical Activity Level. When energy intake is lower than energy needs, the body adapts by reduc- ing voluntary physical activity, reducing growth rates (in children), and mobi- lizing energy reserves, primarily adipose tissue, which in turn leads to weight loss. In adults, an abnormally low BMI is associated with decreased work ca- pacity and limited voluntary physical activity. When energy intake is higher than energy needs, weight gain occurs and consequently chronic disease risk increases, including risk of Type II diabetes, hypertension, coronary heart disease (CHD), stroke, gallbladder disease, os- teoarthritis, and some types of cancer. ENERGY AND THE BODY Function Energy is required to sustain the body’s various functions, including respira- tion, circulation, metabolism, physical work, and protein synthesis.

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PART II: ENERGY 85 Background Information Energy in foods is released in the body through the oxidation of various organic substances, primarily carbohydrates, fats, and amino acids, yielding the chemi- cal energy required to sustain metabolism, nerve transmission, respiration, cir- culation, physical work, and other bodily functions. The heat produced during oxidation is used to maintain body temperature. Carbohydrate, fat, protein, and alcohol provide all of the energy supplied by foods and are generally referred to as macronutrients (in contrast to vitamins and elements, which are referred to as micronutrients). The amount of energy released by the oxidation of macronutrients is shown in Table 3. ENERGY VERSUS NUTRIENTS For many nutrients, a Recommended Dietary Allowance (RDA) is calculated by adding two standard deviations (SD) to the median amounts that are sufficient to meet a specific criterion of adequacy in order to meet the needs of nearly all healthy individuals (see Part I, “Introduction to the Dietary Reference Intakes”). However, this is not the case with energy because excess energy cannot be elimi- nated and is eventually deposited in the form of body fat. This reserve provides a means to maintain metabolism during periods of limited food intake, but it can also result in obesity. Therefore, it seems logical to base estimated energy intake on the amounts of energy that need to be consumed to maintain energy balance in adults who maintain desirable body weights, also taking into account the increments in energy expenditure elicited by their habitual level of activity. There is another fundamental difference between the requirements for en- ergy and those for nutrients. A person’s body weight is a readily monitored indicator of the adequacy or inadequacy of habitual energy intake. A compara- TABLE 3 Energy Provided by Macronutrients Kcal/ga Macronutrient Carbohydrate 4 Fat 9 Protein 4 Alcoholb 7 a These values for carbohydrate, fat, protein, and alcohol are known as Atwater Factors. Atwater, a pioneer in the study of nutrients and metabolism, proposed the use of these values. They are often used in nutrient labeling and diet formulation. b The alcohol (ethanol) content of beverages is usually described in terms of percent by volume. One mL of alcohol weighs 0.789 g and provides 5.6 kcal/mL.

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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 86 bly obvious and individualized indicator of inadequate or excessive intake is not usually evident for other nutrients. BODY MASS INDEX Body mass index, or BMI, is defined as weight in kilograms divided by the square of height in meters. A growing body of literature supports the use of BMI as a predictor of the impact of body weight on morbidity and mortality risks. The National Institutes of Health (NIH) and the World Health Organization (WHO) have defined BMI cutoffs for adults over 19 years of age, regardless of age and gender: underweight is defined as a BMI of less than 18.5 kg/m2, over- weight as a BMI from 25 up to 30 kg/m2, and obese as a BMI of 30 kg/m2 or higher. A healthy or desirable BMI is considered to be from 18.5 kg/m2 up to 25 kg/m2. This range of BMI is used in deriving the equations for estimating the energy requirement. Components of Energy Expenditure Basal and resting metabolism: The basal metabolic rate (BMR) reflects the en- ergy needed to sustain the metabolic activities of cells and tissues, plus the energy needed to maintain blood circulation, respiration, and gastrointestinal and renal function while awake, in a fasting state, and resting comfortably (i.e., the basal cost of living). BMR includes the energy expenditure associated with remaining awake, reflecting the fact that the sleeping metabolic rate (SMR) dur- ing the morning is some 5–10 percent lower than BMR during the morning hours. BMR is commonly extrapolated to 24 hours and is then called basal energy expenditure (BEE), expressed as kcal per 24 hours. Resting metabolic rate (RMR) reflects energy expenditure under resting conditions and tends to be somewhat higher (10–20 percent) than under basal conditions, due to the increases in energy expenditure caused by recent food intake (i.e., by the thermic effect of food) or by the delayed effect of recently completed physical activity. Basal, resting, and sleeping energy expenditures are related to body size, being most closely correlated with the size of fat-free mass (FFM), which is the weight of the body less the weight of its fat mass. The size of the FFM generally explains 70–80 percent of the variance in RMR among individuals. However, RMR is also affected by age, gender, nutritional state, inherited variations, and differences in the endocrine state. Thermic effect of food: The thermic effect of food (TEF) refers to the increased energy expenditure caused by food consumption, including its digestion, trans- port, metabolization, and storage. The intensity and duration of meal-induced

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PART II: ENERGY 87 TEF are primarily determined by the amount and composition of the foods consumed, mainly due to the metabolic costs of handling and storing ingested nutrients. The increments in energy expenditure during digestion above baseline rates, divided by the energy content of the food consumed, vary from 5 to 10 percent for carbohydrate, 0 to 5 percent for fat, and 20 to 30 percent for pro- tein. The high TEF for protein reflects the relatively high metabolic cost in- volved in processing the amino acids. The TEF for a mixed diet is 10 percent of the food’s energy content. Thermoregulation: This is the process by which mammals regulate their body temperature within narrow limits. Because most people can adjust their cloth- ing and environment to maintain comfort, the additional energy cost of ther- moregulation rarely has an appreciable effect on total energy expenditure. Physical activity: The energy expended for physical activity varies greatly among individuals and from day to day. In sedentary people, about two-thirds of total energy expenditure (TEE) goes to sustain basal metabolism over 24 hours (the BEE), while one-third is used for physical activity. In very active people, 24- hour TEE can rise to twice as much as BEE, while even higher total expendi- tures can occur among heavy laborers and some athletes. In addition to the immediate energy cost of individual activities, exercise induces a small increase in energy expenditure that persists for some time after an activity has been completed. The body’s excess post-exercise oxygen con- sumption (EPOC) depends on exercise intensity and duration and has been estimated at some 15 percent of the increment in expenditure that occurs dur- ing the activity. Physical activity level: The ratio of total to basal daily energy expenditure (TEE:BEE) is known as the Physical Activity Level (PAL). PAL categories are defined as sedentary (PAL ≥ 1.0 < 1.4), low active (PAL ≥ 1.4 < 1.6), active (PAL ≥ 1.6 < 1.9), and very active (PAL ≥ 1.9 < 2.5). In this publication, PAL is used to describe and account for physical activity habits (see Part II, “Physical Activity”). Total energy expenditure: Total energy expenditure (TEE) is the sum of the basal energy expenditure, the thermic effect of food, physical activity, thermoregu- lation, and the energy expended in depositing new tissues and in producing milk. With the emergence of information on TEE by the doubly labeled water method, it has become possible to determine the energy expenditure of infants, children, and adults in free-living conditions. It refers to energy expended dur- ing the oxidation of energy-yielding nutrients to water and carbon dioxide.

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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 88 DETERMINING DRIS Estimated Energy Requirement The Estimated Energy Requirement (EER) is defined as the average dietary en- ergy intake that is predicted to maintain energy balance in a healthy adult of a defined age, gender, weight, height, and a level of physical activity that is con- sistent with good health. There is no RDA for energy because energy intakes above the EER would be expected to result in weight gain. To calculate the EER for adults, prediction equations for normal-weight individuals (BMI of 18.5–25 kg/m2) were developed using data on total daily energy expenditure as measured by the DLW technique (see Table 1). In chil- dren and in pregnant or lactating women, the prediction equations for the EER account for the additional needs associated with the deposition of tissues or the secretion of milk at rates that are consistent with good health. Criteria for Determining Energy Requirements, by Life Stage Group Life stage group Criterion 0 through 6 mo Energy expenditure plus energy deposition 7 through 12 mo Energy expenditure plus energy deposition 1 through 18 y Energy expenditure plus energy deposition > 18 y Energy expenditure Pregnancy 14 through 18 y Adolescent female EER plus change in TEE plus pregnancy energy deposition 19 through 50 y Adult female EER plus change in TEE plus pregnancy energy deposition Lactation 14 through 18 y Adolescent female EER plus milk energy output minus weight loss 19 through 50 y Adult female EER plus milk energy output minus weight loss Factors That Affect Energy Expenditure and Requirements Body composition and body size: Although body size and weight exert appar- ent effects on energy expenditure, it is disputed whether differences in body composition quantitatively affect energy expenditure. It is unlikely that body

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PART II: ENERGY 89 composition markedly affects energy expenditure at rest or the energy costs of physical activity in adults with BMIs of 18.5–25 kg/m2. In adults with higher percentages of body fat, mechanical hindrances can increase the energy expen- diture associated with certain activities. The proportion of fat-free mass (FFM) is the major parameter in determin- ing the rate of energy expenditure under fasting basal metabolic rate (BMR) and resting metabolic rate (RMR) conditions. RMR/kg of weight or RMR/kg of FFM falls as mass increases because the contributions made by the most metaboli- cally active tissues (the brain, liver, and heart) decline as body size increases. Findings from different studies suggest that low energy expenditure is a risk factor for weight gain in a subgroup of people susceptible to excess weight gain, but not in all susceptible people and not in those with a normal level of risk. These data are consistent with the general view that obesity is a multi- factorial problem. Physical activity: The increased energy expenditure that occurs during physi- cal activity accounts for the largest part of the effect of activity on overall energy expenditure. Physical activity also affects energy expenditure in the post-exercise period, depending on exercise intensity and duration, environmental tempera- tures, one’s state of hydration, and the degree of trauma to the body. This effect lasts for as many as 24 hours following exercise. Spontaneous non-exercise activity reportedly accounts for 100–700 kcal/ day. Sitting without fidgeting or sitting with fidgeting raises energy expenditure by 4 or 54 percent, respectively, compared with lying down. Standing while motionless or standing while fidgeting raises energy expenditure by 13 or 94 percent, respectively. Gender: There are substantial data on the effects of gender on energy expendi- ture throughout the lifespan. Gender differences in BMR are due to the greater level of body fat in women and to differences in the relationship between RMR and FFM. Growth: Energy requirements in infants and children include the energy asso- ciated with the deposition of tissues at rates consistent with good health. The energy cost of growth as a percentage of total energy requirements decreases from around 35 percent at age 1 month to 3 percent at age 12 months. It re- mains low until the adolescent growth spurt, when it then increases to about 4 percent. The timing of the adolescent growth spurt, which typically lasts 2 to 3 years, is also very variable, with the onset typically occurring between ages 10 and 13 years in the majority of children.

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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 90 Older age: All three major components of energy expenditure (RMR, TEF and, energy expenditure of physical activity [EEPA]), decrease with aging. There is an average 1–2 percent decline per decade in men who maintain constant weight. The suggested breakpoint for a more rapid decline appears to occur at approxi- mately age 40 years in men and age 50 years in women. For women, this may be due to an accelerated loss of FFM during menopause. PAL has been shown to progressively decrease with age and is lower in elderly adults compared to young adults. Genetics: Individual energy requirements substantially vary due to combina- tions of differences in body size and composition; differences in RMR indepen- dent of body composition; differences in TEF; and differences in physical activ- ity and EEPA. All of these determinants of energy requirement are potentially influenced by genetics, with cultural factors also contributing to variability. Ethnicity: Data from studies of adults and children indicate that the BMR is usually lower in African Americans than Caucasians. Currently, insufficient data exist to create accurate prediction equations of BMRs for African American adults. In this publication, the general prediction equations in Table 1 are used for all races, recognizing their potential to overestimate BMR in some groups such as African Americans. Environment: There is a modest 2–5 percent increase in sedentary TEE at low- normal environmental temperatures (20–28∞C, or 68–82∞F) compared with high-normal temperatures (28–30∞C, or 82–86∞F). However, in setting energy requirements, no specific allowance was made for environmental temperatures. The TEE values used to predict energy requirements can be considered values that have been averaged for the environmental temperatures of different sea- sons. High altitude also increases BMR and TEE due to the hypobaric hypoxia. However, it is unclear at which heights the effect becomes prominent. Adaptation and accommodation: Adaptation implies the maintenance of essen- tially unchanged functional capacity in spite of some alteration in a steady-state condition, and it involves changes in body composition that occur over an ex- tended period of time. The term adaptation describes the normal physiological responses of humans to different environmental conditions. An example of ad- aptation is the increase in hemoglobin concentration that occurs when indi- viduals live at high altitudes. Accommodation refers to relatively short-term adjustments that are made to maintain adequate functional capacity under altered steady-state conditions. The term accommodation characterizes an adaptive response that allows sur-

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PART II: ENERGY 91 vival but results in some consequences on health or physiological function. The most common example of accommodation is a decrease in growth velocity in children. By reducing growth rate, children’s bodies are able to save energy and may subsist for prolonged periods of time on marginal energy intakes, although this could be at the cost of eventually becoming stunted. The estimation of energy requirements from energy expenditure implicitly assumes that the effi- ciency of energy use is more or less uniform across all individuals, an assump- tion that is supported by experimental data. The UL The Tolerable Upper Intake Level (UL) is the highest daily nutrient intake that is likely to pose no risk of adverse effects for almost all people. The UL concept does not apply to energy because intake above an individual’s energy require- ments would lead to weight gain and likely increased risk of morbidity. EFFECTS OF UNDERNUTRITION Undernutrition is still a common health concern in many parts of the world, particularly in children. When energy intake does not match energy needs due to insufficient dietary intake, excessive intestinal losses, or a combination thereof, several mechanisms of adaptation come into play. A reduction in voluntary physical activity is a rapid means to reduce energy output. In children, a reduc- tion in growth rate is another mechanism to reduce energy needs. However, if this condition persists in children, low growth weight results in short stature and low weight-for-age, a condition known as stunting. A chronic energy defi- cit elicits the mobilization of energy reserves, primarily adipose tissue, which leads to changes in body weight and body composition over time. In children, the effects of chronic undernutrition include decreased school performance, delayed bone age, and an increased susceptibility to infections. In adults, an abnormally low BMI is associated with decreased work capacity and limited voluntary physical activity. ADVERSE EFFECTS OF OVERCONSUMPTION Two major adverse effects result from the overconsumption of energy: • Adaptation to high levels of energy intake: When people are given a diet providing a fixed, but limited, amount of excess energy, they initially gain weight. However, over a period of several weeks, their energy ex- penditure will increase, mostly because of their increased body size. As such, their body weight will eventually stabilize at a higher weight level.

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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 92 Reducing energy intake will produce the opposite effect. For most indi- viduals, it is likely that the main mechanism for maintaining body weight is controlling food intake rather than adjusting physical activity. • Increased risk of chronic disease: A BMI of ≥ 25 kg/m2 is associated with an increased risk of premature mortality. In addition, as BMI increases be- yond 25 kg/m2, morbidity risk increases for Type II diabetes, hyperten- sion, coronary heart disease (CHD), stroke, gallbladder disease, osteoar- thritis, and some types of cancer. Because some studies suggest that disease risk begins to rise at lower BMI levels, some investigators have recommended aiming for a BMI of 22 kg/m2 at the end of adolescence. This level would allow for some weight gain in mid-life without sur- passing the 25 kg/m2 threshold. For the above reasons, energy intakes associated with adverse risks are defined as those that cause weight gain in individuals with body weights that fall within the healthy range (BMI of 18.5–25 kg/m2) and overweight individuals (BMI of 25–30 kg/m2). In the case of obese individuals who need to lose weight to improve their health, energy intakes that cause adverse risks are those that are higher than intakes needed to lose weight without causing negative health consequences. KEY POINTS FOR ENERGY Energy is required to sustain the body’s various functions, 3 including respiration, circulation, metabolism, physical work, and protein synthesis. A person’s energy balance depends on his or her dietary 3 energy intake and total energy expenditure, which includes the basal energy expenditure, the thermic effect of food, physical activity, thermoregulation, and the energy expended in depositing new tissues and in producing milk. Imbalances between energy intake and expenditure result in 3 the gain or loss of body components, mainly in the form of fat. These gains or losses determine changes in body weight. The EER is the average dietary energy intake that is predicted 3 to maintain energy balance in a healthy adult of a defined age, gender, weight, height, and a level of physical activity that is consistent with good health. In children and in pregnant and lactating women, the EER 3 accounts for the needs associated with growth, deposition of tissues, and the secretion of milk at rates that are consistent with good health.

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PART II: ENERGY 93 A person’s body weight is a readily monitored indicator of the 3 adequacy or inadequacy of habitual energy intake. Numerous factors affect energy expenditure and requirements, 3 including age, body composition, gender, and ethnicity. There is no RDA for energy because energy intakes above the 3 EER would be expected to result in weight gain. The UL concept does not apply to energy because any intake 3 above a person’s energy requirements would lead to undesirable weight gain. When energy intake is less than energy needs, the body adapts 3 by mobilizing energy reserves, primarily adipose tissue. In adults, an abnormally low BMI is associated with decreased 3 work capacity and limited voluntary physical activity. The overconsumption of energy leads to the adaptation to high 3 levels of energy intake with weight gain and an increased risk of chronic diseases, including Type II diabetes, hypertension, CHD, stroke, gallbladder disease, osteoarthritis, and some types of cancer.