Obesity in the UK was assumed to have developed against a population decline in physical activity, with health messages focused on diet and exercise prevention strategies. Doubly-labelled water (DLW) studies of energy expenditure have indicated the alternative scenario that the increased obesity prevalence reflects excessive food energy intake with physical activity levels unchanged. This analysis is questionable, deriving in part from a weakness of the DLW methodology in identifying changing physical activity levels within populations of increasing body weight. This has resulted in an underestimation of the reduction in physical activity in the overweight and obese, as revealed by direct studies of such behaviour. Furthermore, a close examination of food energy supply, household food purchases and individual food energy consumption since 1955, in relation to likely estimates of current intakes indicated by simple modelling of predicted energy expenditure, identifies: (a) food energy supply as markedly overestimating energy intakes; (b) individual food energy consumption as markedly underestimating energy intakes; and (c) household food purchase data as the closest match to predicted current food energy intakes. Energy intakes indicated by this latter method have fallen by between 20 to 30 %, suggesting comparable falls in physical activity. Although unequivocal evidence for a matching UK trend in falling physical activity is limited, as is evidence that obesity follows reductions in physical activity, such a link has been recently suggested in a large prospective study in adolescents. Thus, for the UK, obesity has developed within a ‘move less–eat somewhat less but still too much’ scenario. A focus on both diet and exercise should remain the appropriate public health policy.

The objective of the present study was to investigate the relationship between the indices of body size such as BMI, fat-free mass index (FFMI, FFM/height2), fat mass index (FMI, FM/height2), and body fat percentage (%BF), and physical activities assessed by the doubly-labelled water (DLW) method and an accelerometer in free-living Japanese adult women. We conducted a cross-sectional study in 100 female subjects ranging in age from 31 to 69 years. Subjects were classified in quartiles of BMI, FFMI, FMI and %BF. Daily walking steps and the duration of light to vigorous physical activity were simultaneously assessed by an accelerometer for the same period as the DLW experiment. Only physical activity-related energy expenditure (PAEE)/FFM and PAEE/body weight (BW) decreased in the highest quartile of BMI. Physical activity level, PAEE/FFM and PAEE/BW decreased in the highest quartile of FMI and %BF, whereas they were not different among quartiles of FFMI. Daily walking steps and the duration of moderate- and vigorous-intensity physical activities decreased or tended to decrease in the highest quartile of FMI and %BF, but did not differ among quartiles of FFMI and BMI. These results clearly showed that Japanese adult women with higher fat deposition obviously had a low level of physical activities assessed by both the DLW method and accelerometry, but those with larger BMI had lower PAEE/FFM and PAEE/BW only. Our data suggest that the relationship between obesity and daily physical activities should be discussed using not only BMI but also FMI or %BF.

Our understanding of human energy metabolism has benefited greatly from the application of water labelled with 2H and 18O for the measurement of total body water, water turnover and total daily energy expenditure. Applications include validation of techniques for the assessment of dietary intake and physical activity, assessment of water and energy requirement and the assessment of the effect of dietary and physical activity interventions, including its use with endurance athletes competing at the highest level. Critical aspects of the application are isotope dose preparation, sample collection, sample analysis and the calculation procedure. The labelled-water method can easily be applied in normal living conditions, including exercise, and in the clinical setting. However, sample analysis requires a sophisticated laboratory with an isotope-ratio mass spectrometer and a sample preparation system. Examples of insights based on labelled-water studies are: (1) self-reported dietary intakes often underestimate energy requirements; (2) subjects have problems maintaining energy balance when daily energy expenditure exceeds 2.5 times resting energy expenditure. Devices for the assessment of physical activity validated using labelled water allow the study of activity patterns and strategies to influence the activity level of a sedentary society.

Activity intensity is a potential determinant of activity-induced energy expenditure. Tri-axial accelerometery is the most objective measurement technique for the assessment of activity intensity, in combination with doubly-labelled water for the measurement of energy expenditure under free-living conditions. Data on the effects of subject characteristics, including body size and age, and exercise training on the relationship between activity intensity and daily energy expenditure are reviewed. Average daily metabolic rate and non-basal energy expenditure are positively related to body size. The duration and intensity of physical activities do not need to be equivalent to the energy spent on activity. Obese subjects spend more energy on physical activity but can perform fewer activities, especially high-intensity (weight-bearing) activities, because of their higher body weight. Physical activity generally declines gradually from about 60 years of age onwards. Most subjects >80 years have an activity level well below the level defined for sedentary middle-aged adults. Spending relatively more time on low-intensity activities has a negative effect on the mean physical activity level. To obtain a higher physical activity level does not necessarily imply high-intensity activities. In an average subject 25% of the activity-induced energy expenditure may be attributed to high-intensity activities. Exercise training, as a form of high-intensity activity, affects the physical activity level more in younger subjects than in elderly subjects.

The prevalence of obesity in children, as in adults, is increasing dramatically. The extent to which this is due to reduced energy expenditure, increased energy intake, or both, is unclear at present. This in part reflects the limitations of existing models of the pre-obese state. In childhood acute lymphoblastic leukaemia (ALL), patients typically gain weight excessively during and after 2 years of therapy, and are at high risk of becoming obese. Previous studies have failed to identify the cause of obesity in these patients. We have tested the hypothesis that excess weight gain in ALL is due to reduced total energy expenditure (TEE), measured using the doubly-labelled water method, and have identified risk factors for excess weight gain in ALL. Pre-obese children with ALL in the dynamic phase of weight gain are less physically active than their peers, with a reduced TEE of approximately 1.2 (95 % CI 0.2, 2.2) MJ/d. While other factors might contribute to excess weight gain, lifestyle (i.e. reduced habitual physical activity) plays a central role in ALL. Several considerations suggest that ALL might be a useful model of the pre-obese state: lifestyle is critical to development of obesity in ALL; ALL is relatively common; approximately 70 % of patients survive; patients are readily accessible during the 2 years of therapy and beyond.

Body fatness and the components of energy expenditure in children aged 5–14 years were investigated. In a group of seventy-nine healthy children (thirty-nine female, forty male), mean age 10·0 (sd 2·8) years, comprising twenty-seven Maori, twenty-six Pacific Island and twenty-six European, total energy expenditure (TEE) was determined over 10 d using the doubly-labelled water method. Resting metabolic rate (RMR) was measured by indirect calorimetry and physical activity level (PAL) was calculated as TEE:RMR. Fat-free mass (FFM), and hence fat mass, was derived from the 18O-dilution space using appropriate values for FFM hydration in children. Qualitative information on physical activity patterns was obtained by questionnaire. Maori and Pacific children had a higher BMI than European children (P<0·003), but % body fat was similar for the three ethnic groups. The % body fat increased with age for girls (r 0·42, P=0·008), but not for boys. Ethnicity was not a significant predictor of RMR adjusted for FFM and fat mass. TEE and PAL, adjusted for body weight and age, were higher in Maori than European children (P<0·02), with Pacific children having intermediate values. PAL was inversely correlated with % body fat in boys (r −0·43, P=0·006), but was not significantly associated in girls. The % body fat was not correlated with reported time spent inactive or outdoors. Ethnic-related differences in total and activity-related energy expenditure that might account for higher obesity rates in Maori and Pacific children were not seen. Low levels of physical activity were associated with increased body fat in boys but not in girls.

According to the report of the World Health Organization (1985), total energy expenditure (TEE) in human subjects can be calculated as BMR×physical activity level (PAL). However, other reports have pointed out limitations in the suggested procedure related to the % body fat of the subjects. The purpose of the present study was to evaluate the World Health Organization (1985) procedure in thirty-four healthy women with BMI 18–39kg/m2. BMR and TEE were measured using indirect calorimetry (BMRmeas) and the doubly-labelled water method (TEEref) respectively. When assessed using the doubly-labelled water and skinfold-thickness methods, the women had 34 (sd 8) and 33 (sd 6) % body fat respectively. On the basis of guidelines provided by the World Health Organization (1985), 1·64 was selected to represent the average PAL of the women. Furthermore, PAL was also assessed by means of an accelerometer (PALacc), heart-rate recordings (PALHR) and a questionnaire (PALq). These estimates were: PALacc 1·71 (sd 0·17), PALHR 1·76 (sd 0·24), PALq 1·86 (sd 0·27). These values were lower than TEEref/BMRref, which was 1·98 (sd 0·21). BMR assessed using equations recommended by the World Health Organization (1985) (BMRpredicted) overestimated BMR by 594 (sd 431) kJ/24h. However, when TEE was calculated as BMRpredicted×PALacc, BMRpredicted×PALHR and BMRpredicted×PALq respectively, average results were in agreement with TEEref. Furthermore, TEE values based on BMRpredicted and PALacc, PALHR, PALq as well as on PAL=1·64, minus TEEref, were significantly correlated with body fatness. When the same PAL value (1·64) was used for all subjects, this correlation was particularly strong. Thus, the World Health Organization (1985) procedure may give TEE results that are biased with respect to the body fatness of subjects.

The accuracy of the multiple pass 24 h recall for assessment of habitual energy intake in pre-school children is unclear. The primary aim of this study was to assess its accuracy by comparison with measurement of total energy expenditure by doubly-labelled water in a representative sample of forty-one 3–4-year-olds. The recall method was well tolerated by subjects and was administered quickly and easily. However, it produced estimates of energy intake which significantly exceeded measures of total energy expenditure from doubly-labelled water, mean paired difference 660 kJ/d (P<0·01). Agreement between the two methods was poor at the individual level: limits of agreement 660+/-3018 kJ/d. Error and imprecision in both methods contribute to individual differences, but the present study suggests that the multiple pass 24 h recall does not provide accurate estimates of dietary energy intake in individual children.

We validated doubly-labelled water (DLW) by comparison to indirect calorimetry and food intake–mass balance in eight Labrador dogs (24–32 kg) over 4 d. We used several alternative equations for calculating CO2 production, based on the single- and two-pool models and used two alternative methods for evaluating the elimination constants: two-sample and multiple-sampling. In all cases the DLW technique overestimated the direct estimate of CO2 production. The greatest overestimates occurred with the single-pool model. Using two samples, rather than multiple samples, to derive the elimination constants produced slightly more discrepant results. Discrepancies greatly exceeded the measured analytical precision of the DLW estimates. The higher values with DLW probably occurred because the dogs were extremely active during the 1 h in each 24 spent outside the chamber. Estimates of CO2 production from food intake–mass balance, which include this activity, produced a much closer comparison to DLW (lowest mean discrepancy 0·3 % using the observed group mean dilution space ratio and an assumption that the mass changes reflected changes in hydration for all except one animal). We recommend an equilibration time of 6 h and use of the two-pool model based on the observed population dilution space for future studies of energy demands in dogs of this body mass.

There is a limited knowledge concerning energy requirements of the elderly, especially the oldest old (> 80 years). Energy requirements should be estimated from measurements of energy expenditure. For this purpose twenty-one free-living individuals (eight males, thirteen females) aged 91–96 years living in Göteborg, Sweden were studied. Total body water (TBW) measured by the doubly-labelled-water (DLW) technique was 29·5 (SD 5·4) KG IN FEMALES AND 35·6 (sd 4·3) kg in males. TBW measured using bioelectric impedance (BIA) was 31·6 (sd 6·4) kg in females and 42·0 (sd 7·4) kg in males. The mean difference between TBW measured by BIA and that measured by DLW was 3·54 (sd 3·6) kg (P = 0·0002). Resting metabolic rate (RMR) was measured using a ventilated-hood system and averaged 5·36 (sd 0·71) MJ/d in females (n 12) and 6·09 (sd 0·91) MJ/d in males (n 8). Difference between measured RMR and predicted BMR (n 20) was 0·015 (sd 0·86) MJ/d (NS). Total energy expenditure (TEE) measured by DLW averaged 6·3 (sd 0·81) MJ/d in females and 8·1 (sd 0·73) MJ/d in males. Activity energy expenditure (TEE - RMR), thus including diet-induced thermogenesis (DIT), averaged 0·95 (sd 0·95) MJ/d in females (n 12) and 2·02 (sd 1·13) MJ/d in males. Physical activity level (TEE/BMR) averaged 1·19 (sd 0·19) in females and 1·36 (sd 0·21) (P = 0·08) in males. If DIT is assumed to be 10 % of the TEE, energy spent on physical activity will be very low in this population.

The purpose of the present study was to estimate whole-body fatty acid and cholesterol synthesis in weight-stable adults and to determine the likely effect on the doubly-labelled water (DLW) method for measuring energy expenditure. Synthesis was measured by 2H incorporation over 14 d in six adult males in approximate energy balance following noradrenaline infusion to maximize mobilization of free fatty acid from adipose tissue. The inter-individual variation in synthesis rates was large and in one subject the proportion of free fatty acid synthesized was ten times that of the mean of the rest of the group; the fasting concentration of esterified fatty acid in this subject was five times that of the rest of the group indicating likely violation of the assumptions underlying the calculation of whole-body synthesis. After 14 d of labelling in the other five subjects, 0·9 (SEM 0·3) % OF THE CIRCULATING FREE FATTY ACID, 9·3 (sem 3·0) % of the esterified fatty acid, 14·6 (sem 2·4) % of the free cholesterol and 28·3 (sem 3·7) % of esterified cholesterol had been synthesized de novo. A high rate of synthesis correlated with a low pre-dose 2H abundance both within and between lipid classes suggesting that natural 2H abundance variations in some lipid classes may be used to determine their metabolic origin. Whole-body synthetic rates were 8 g/d for fatty acid and 0·3–0·5 g/d for cholesterol. These values correspond to very small errors on DLW-derived estimates of CO2 production; -2·5 litres/d for fatty acid and -0·1 to -0·2 litres/d for cholesterol. These results, obtained in subjects typically consuming a diet with a lower fat and cholesterol content that the typical Western diet, suggest that the DLW method is unlikely to be affected by fatty acid and cholesterol synthesis in subjects in energy balance consuming a typical Western diet.

Energy expenditure was estimated using the doubly-labelled water (DLW) method in summer in five free-living adult, non-pregnant, non-lactating, red deer (Cervus elaphus) hinds (weight 107.3 (se 0.9) kg; age 6 (se 1) years) on lowland pasture under typical farming conditions. Climatic conditions were monitored throughout the experiment. Errors due to 2H losses in CH4 and faeces were calculated from previous estimates of stoichiometries. CH4 production, fractionated water loss, urinary N and O2 consumption were estimated using an iterative approach. The water flux (rH2O) in these animals consuming only fresh grass was 12 (se 0.5) kg/d, the CO2 production (rCO2) was 1271 (se 4.0) litres/d and the mean energy expenditure was 25 (se 0.8) MJ/d. There were no significant differences in the isotope distribution spaces and flux rates, rH2O, rCO2 or energy expenditure using the multi-point or two-point approaches to calculation. The DLW-derived energy expenditure of 25 MJ/d is approximately 20% higher than the recommended intake of 21 MJ/d for adult hinds kept outdoors (Adam, 1986) and, at 757 kJ/kg0.75 per d, one third higher than the value of 570 kJ/kg0.75 per d for stags penned indoors (Key et al. 1984).

Free-living energy expenditure was estimated by doubly-labelled water (DLW) and continuous heart-rate (HR) monitoring over nine consecutive days in nine healthy men with sedentary occupations but different levels of leisure-time physical activity. Individual calibrations of the HR-energy expenditure (EE) relationship were obtained for each subject using 30 min average values of HR and EE obtained during 24h whole-body calorimetry with a defined exercise protocol, and additional data points for individual leisure activities measured with an Oxylog portable O2 consumption meter. The HR data were processed to remove spurious values and insert missing data before the calculation of EE from second-order polynomial equations relating EE to HR. After data processing, the HR-derived EE for this group of subjects was on average 0.8 (sem 0.6) MJ/d, or 6.0 (sem 4.2)% higher than that estimated by DLW. The diary-respirometer method, used over the same 9d, gave values which were 1.9 (sem 0.7) MJ/d, or -12.1 (sem 4.0)% lower than the DLW method. The results suggest that HR monitoring can provide a better estimate of 24 h EE of groups than the diary-respirometer method, but show that both methods can introduce errors of 20% or more in individuals.

The present study was designed to investigate the interaction between body weight and energy expenditure in well-nourished individuals. Energy expenditure was determined during a 10 d highly controlled work programme in apparently well-nourished adult male construction workers with a wide range of body weights (mean weight: 63·9 (SD 11·0, range 46·7-80·1) kg, mean BMI: 22·5 (SD 3·8, range 16·7-28·9) kg/m2). Total energy expenditure (mean: 12·68 (SE 0·73) MJ/d or 1·78 (SE 0·07) x BMR) was determined using doubly-labelled water and the energy costs of work activities by Oxylog. The energy expenditure during work (mean: 5·75 (SE 0·29) MJ/day or 3·48 (SE 0·09) x BMR) was estimated from the energy costs of individual tasks and the time spent in those tasks. The energy expenditure during discretionary time (mean: 4·37 (SE 0·58) MJ/d or 1·49 (SE 0·17) x BMR) was calculated by subtracting occupation and sleep expenditure (taken as1 x BMR) from total expenditure. Food intake and discretionary time allocation were recorded by the subjects. The energy expenditure in the programmed work activities (expressed as a multiple of BMR) showed a significant increase (P=0·035) with increasing body weight, suggesting that the assumed constancy of BMR multiples across a wide range of body weights may not be valid. This assertion was supported by theoretical calculations based on empirically derived equations. In order to avoid errors which could be interpreted as metabolic ‘adaptation’ it may be necessary to take account of body weight when using the BMR-multiple approach to estimate energy requirements at low body weights.

Energy expenditure was measured over 10 d using the doubly-labelled water (DLW) and activity diary methods in summer and winter in subjects with ‘light’ occupations but leisure activities which ranged from ‘non-active’ to ‘very active’. The basal metabolic rate (BMR) and the energy cost of activities were determined by indirect calorimetry. The Department of Health (1991) predicted BMR for the group (6·89 (SD 0·30) MJ/d; n 18) was not significantly different from the measured value (7·17 (SD 0·70) MJ/d; n 18). The range of DLW-derived expenditure values within the group was BMR X 1·41 to 2·41. The largest seasonal change within individuals was BMR X 0·5. The energy expenditure of the group as a whole was lower in winter (BMR X 1·88; SD 0·33; n 9) than summer (BMR X 2·01; SD 0·30; n 9) though the difference was not statistically significant. The average summer and winter DLW-derived expenditure was BMR X 1·96 (SD 0·31; n 17). The activity diary estimate of expenditure was BMR X 1·79 (SD 0·32; n 17). In a subset of the group who were representative of the most active 26% of all adult males in the UK, the DLW-derived expenditure was BMR X 2·08 (SD 0·24; n 11). This is higher than the highest Department of Health (1991) estimate of BMR X 1·6 for individuals in light occupations. The measured energy costs of low-intensity activities were similar to those presented in the Department of Health (1991) report but the value determined for running (BMR X 13·08; SD 2·4; n 6) was higher than the highest value in the report (BMR X 6 to 8). The results indicate that the recent Department of Health (1991) reference values for energy may underestimate the expenditure of a significant proportion of the UK population largely because the energy costs of activity used in the report to calculate expenditure do not accurately reflect those achieved during active leisure in individuals who take regular exercise.

Measurement of energy expenditure with doubly-labelled water and of body composition and breast milk output with 2H or 18O requires accurate and precise techniques for measuring isotopic enrichments. The possibility of an inaccuracy in measurements of 2H and 18O isotopic enrichment arising from the matrix in biological fluids was investigated (1) by simulating a dilution experiment in both water and urine samples and (2) by reconstituting urine samples, ranging from 10 to 60 g/kg in solid concentration, from freeze-dried urinary solids mixed with either natural abundance or doubly-labelled water. Current techniques involved in measuring 2H and 18O isotopic enrichments were used (reduction of the samples to H2 gas with either Zn or U, and CO2/H2O equilibration or direct measurement of mass 20:18 ratios on water vapour for 18O analysis). All four methods accurately measured serial dilutions in both urine and water. Dilution space calculated from isotopic enrichments, compared with the water content of urine (determined by freeze-drying and accounting for exchangeable isotopes) was overestimated by about 2.4 % by the Zn technique whereas other methods were accurate. The urinary solids content of a water solution was related to that inaccuracy. The use of the Zn technique with biological samples is likely to create biases in 2H distribution space. Examination of recent literature supports this view. Caution should therefore be used when physiological conclusions have to be made from the relative size of 2H and 18O distribution spaces.

The doubly-labelled water (2H218O) technique was used to assess the long-term rates of energy expenditure and, after accounting for any changes in body composition, the derived rates of energy intake in weight-stable ‘large-eating’ (n 6) and ‘small-eating’ (n 6) women. The self-reported energy intakes (approximately 11.2 v. 5.6 MJ/d) and energy expenditures (approximately 8.5 v. 12.4 MJ/d) for the ‘large-eating’ and ‘small-eating’ groups respectively, should not be sustainable without significant body-weight changes. 2H218O-assessed rates of energy expenditure for the ‘large-eaters’ (approximately 8.5 MJ/d) and ‘small-eaters’ (approximately 11.3 MJ/d) were in close agreement with the results obtained using 5 d, self-reported activity diaries but the derived rates of energy intake for the ‘large-’ (approximately 8.5 MJ/d) and ‘small-eaters’ (approximately 10.8 MJ/d) were markedly different from those obtained using self-reported, weighed food diaries. When two ‘small-eaters’ were supplied with their self-reported energy intakes (approximately 5 MJ/d) for up to 28 d both subjects lost about 0.75 kg body-weight/week. These results provide no support for the existence of ‘metabolically efficient’ women in the community.