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Total daily energy expenditure (TEE)

Three types of methods have been used to calculate total daily energy expenditure of free-living children and adolescents. Their advantages and limitations have been reviewed by several authors (e.g. Torun, 1984; Durnin, 1990).

(1) Doubly-labeled water. This method has two components: (a) Administration of a marker dose of ²H and ¹⁸O, and measurement of the disappearance of the isotope from the body after several days and (b) Calculation of the food quotient or estimation of the average respiratory quotient during that period of time.

The doubly-labeled water is the most accurate of the three methods. However, there are still some doubts about the appropriateness of the assumptions used for the calculation of energy expenditure. Moreover, the number of children so far studied is very small and restricted to few geographical areas due to the high cost of the isotopes and their analysis. Furthermore, it does not provide information on the patterns of physical activity throughout the day.

(2) Heart rate monitoring. This method has three components. (a) Measurement of heart rate while resting and measurement or estimation of the resting and basal metabolic rates. (b) Determination of the relationship between heart rate and oxygen consumption (or energy expenditure) with light, moderate and moderately heavy workloads. This relationship varies among individuals and must be established for every person who will be studied. (c) Minute-by-minute recording of heart rate.

Table 1 Comparison of total daily energy expenditures (MJ/d) measured with two different heart rate monitoring techniques (three-way analysis of variance with unweighted averages)

Earlier studies used recorders that accumulated all heart beats over some period of time. Average heart rate over 24 h gave unacceptable results due to the poor relationship between heart rate and oxygen consumption at resting and sedentary levels of energy expenditure. However, the method yields acceptable results when the average heart rate is calculated for the period of time when children are awake, and energy expenditure calculated for the remainder of the 24 h from the resting and basal metabolic rates. As shown in Table 1, an analysis of studies by Spurr and collaborators (Spurr et al, 1986; Spurr and Reina, 1988a) indicated that the results with this heart rate accumulation method did not differ from those obtained in similar children with the minute-by-minute rate recording method.

The heart rate monitoring method has been validated with whole body calorimetry and doubly-labeled water. Comparisons varied on an individual basis, but the mean values for groups of individuals were similar to the other methods (Spurr et al, 1988; Ceesay et al, 1989; Livingstone et al, 1990a, 1992a; Emons et al, 1992). Thus, heart rate monitoring can be used to estimate the energy expenditure of groups of children. Minute-by-minute recording also allows, examining the time allocated to different intensities of physical effort.

(3) Time-motion or activity diary techniques. These have two components: (a) assessment of time allocation, which has been explored by direct observations with different timing techniques, by activity records or diaries kept by the subjects or caretakers of young children, and by recall interviews with subjects or caretakers and (b) energy costs of the activities that are observed or recorded, measured by indirect calorimetry or estimated from published values. It should be borne in mind that energy costs of activities published for adults do not apply to children under 15 (Town, 1983, 1990a). Many of the results published with the time motion or diary techniques are questionable due to the inaccuracies inherent in methods based on reporting and in the application of energy cost of activities of adults to calculate energy expenditure of children.

We have based this review and our conclusions on TEE on studies with doubly-labeled water or with appropriate techniques of heart rate monitoring. Some estimates of energy expenditure with time motion/diary techniques were selected as examples to examine the conclusions based on the other two methods.

Another relatively simple way to estimate total daily energy expenditure (TEE), and therefore requirements, of adults was proposed by the 1985 FAO/WHO/UNU Expert Consultation. Sleeping, occupational, discretional, health-promoting and other miscellaneous activities were assigned an energy cost, expressed as multiples of basal metabolic rate ( × BMR) or physical activity level (PAL)¹. A factorial calculation accounting for the time allotted to each of those activities allowed the estimation of the mean PAL in 24 h. For populations engaged in occupational activities of different intensities. TEEs of 1.55, 1.78 and 2.10 × BMR were proposed for men with light, moderate and heavy occupational activities, respectively (FAO/WHO/UNU, 1985). The corresponding factors suggested for women were 1.56, 1.64 and 1.82.

We suggest that a similar approach be used to estimate TEE of groups of children and adolescents with different lifestyles. PAL factors are proposed for those estimates in another section of this document ('Physical activity levels of children and adolescents').

Studies with doubly-labeled water

The doubly-labeled water technique is almost 40 years old, but there are still relatively few data on total energy expenditure in children, due primarily to cost. Until the mid 1970s the cost of the stable isotopes (²H and ¹⁸O) involved in the technique was restrictive. Since that time advances in technology, notably the development of highly precise isotope mass ratio spectrometers, made it possible to administer significantly less isotope, thus reducing the cost to a more manageable figure. Unfortunately, the cost of isotopes began to rise steeply in 1990 and once again fewer studies are being undertaken.

Studies that allow consideration of TEE and dietary recommendations have been done with well-nourished children and adolescents in urban centers of the United Kingdom (Prentice et al, 1988; Davies et al, 1991, 1994), Holland (Saris et al, 1989; Emons et al, 1992) and the United States (Bandini et al, 1990b; Goran et al, 1993; Fontvieille et al, 1993; Wong, 1994). Table 2 shows their age span and TEE expressed per day, per unit of body weight and PAL.

Figure 1 compares the data from Table 2, expressed as kcal/kg/day, with the FAO/WHO/UNU 1985 recommendations, with and without the allowance for growth. The values for energy expenditure shown in the table and figure do not include the small proportion of energy that should be retained for growth (between 1 and 3%, depending on age).

Current dietary energy recommendations are about 20% higher than energy expenditure of children under 7 years of age in industrialized societies. From 7 years onwards, current recommendations coincide reasonably well with the data from doubly-labeled water studies, although boys throughout adolescence and girls around puberty seem to require 5-15% more dietary energy.

¹ Total energy expenditure expressed as × BMR has been considered to reflect an individual's or population's physical activity level (PAL). This term has appeared with increasing frequency in the scientific literature. Thus, we will use it as synonym of × BMR.

Within each sex, the PALs in Table 2 show a trend towards uniformity among children between 1 and 5, 6 and 13, and 14 and more years of age. Therefore, the mean PAL values for those three age groups were calculated (Table 3). Since the studies had similar sample sizes within each age group, calculations of the mean PAL weighted for the number of children in each study gave similar results. Measured BMRs were used for calculations in three studies and BMR estimates with Schofield's equations in all others.

On the average, there were no gender differences at 1-5 and 6-13 years. Boys seemed to have higher PAL than girls after that age, but this observation was based on only three data sets from two studies (Bandini et al, 1990b; Davies et al, 1991). It should also be noted that if PALs were calculated with the equations published by FAO/WHO/UNU (1985) instead of those modified later by Schofield (1985), they would be somewhat lower for girls 1-5 and 6-13 years old than for boys of the same age ranges (1.39 vs 1.47 and 1.74 vs 1.81, respectively).

It should be kept in mind that the values shown in Tables 2 and 3 correspond to studies in a small number of well nourished children with adequate growth patterns, living in societies where food and health services are continuously and readily available.

Table 2 Groups of children, classified by sex and age, whose total daily energy expenditure has been estimated by the doubly labeled water method (does not include 1-3%, depending on age, that should be retained for growth)

^a Range or mean ± standard deviation.
^b Physical Activity Level calculated using basal metabolic rates estimated with Schofield's equations (1985) (or, in parenthesis, measured experimentally).
^c Assuming 50% of the children studied were boys and 50% girls.
^d Assuming the same values for boys and girls.
^e Mean ± s.d.

Table 3 Mean physical activity levels of children in Table 2 grouped by age and sex. (Total energy expenditure measured with doubly labeled water; BMR's were measured or estimated with Schofield's equations)

^a Mean ± s.d. of mean values in Table 2. Number of data sets in parenthesis. Means weighted by the number of children in each study gave similar values.

Studies with heart rate monitoring

Studies to calculate TEE of children and adolescents through heart rate monitoring have also been done only in a few countries, but they include industrialized and developing societies. These studies were done with either daytime heart rate accumulation (Spady, 1980; Torun & Viteri, 1981a,b; Spurr et al, 1986; Spurr & Reina, 1987) or the minute-by-minute heart rate method (Spurr & Reina, 1988a,b, 1989a,b; Livingstone et al, 1992a; Emons et al, 1992; Torun et al, 1993; Ramirez & Torun, 1994). Table 4 shows their age span and results. All studies involved children living in urban centers. Those in Northern Ireland and Holland involved only between 3 and 6 children in each sex-and-age group, and those in Canada were clone with 11 boys and 10 girls. Most studies in Colombia and Guatemala involved 16-34 boys or girls in each age group (median sample size = 20).

Continued

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