Determinants of 24-hour energy expenditure in man. Methods and results using a respiratory chamber

Gender differences in energy expended during activities and in daily energy expenditure of elderly people

Gender effects on energy expended during light seated activities, walking, cycling, and sleep and their consequences on daily energy expenditure (EE) were examined in 11 men and 15 women aged 66.4 +/- 7.1 yr. Two open-circuit whole body calorimeters were used for EE measurements, except for cycling, during which EE was measured separately with the use of a face mask. Lean body mass (determined using H218O dilution method), fat mass, usual physical activity level, and activity intensity (e.g., walking speed and cycling power output) were taken as covariates in the analysis of EE variations before studying gender effects. Sleeping metabolic rate (SMR) and daily EE, adjusted for differences in all covariates, were 11.2 (P = 0.005) and 8.7% (P = 0.071) lower in women than in men, respectively. No gender-related differences were found in the various physical activity EEs above SMR (e.g., gross EE-SMR) [light seated activities (P = 0.790), walking (P = 0.263), and cycling (P = 0.287)] and daily physical activity EE above SMR (P = 0.587) after adjustment for differences in all covariates. Therefore, the lower adjusted daily EE of women could be related to their lower SMR, the most reliable criterion of whole body metabolic rate.

A low sympathoadrenal activity is associated with body weight gain and development of central adiposity in Pima Indian men

To investigate the possible role of impaired sympathetic nervous system and/or adrenal medullary function in the etiology of human obesity, we studied 64 Pima Indian men (28 +/- 6 years, 101 +/- 25 kg, 34 +/- 9% body fat, mean +/- SD) in whom sympathoadrenal function was estimated at baseline by measurements of 24-hour urinary norepinephrine (NE) and epinephrine (Epi) excretion rates under weight-maintenance conditions. Body weight, body composition (hydrodensitometry), and body fat distribution (waist-to-thigh circumference ratio, W/T) were measured at baseline and follow-up. Follow-up data were available on 44 subjects who gained on average 8.4 +/- 9.5 kg over 3.3 +/- 2.1 years. In these subjects, baseline NE excretion rate, adjusted for its determinants (i.e., fat free mass, fat mass, and W/T), correlated negatively with bodyweight gain (r = -0.38; p = 0.009). Baseline Epi excretion rate correlated negatively with changes in W/T (r = -0.44; p = 0.003). In conclusion, our data show for the first time that a flow sympathetic nervous system activity is associated with body weight gain in humans. Also, a low activity of the adrenal medulla is associated with the development of central adiposity.

Effects of alcohol on energy metabolism and body weight regulation: is alcohol a risk factor for obesity?

Some studies have suggested that drinking in moderation may be beneficial for health, but many of these studies do not address body weight. Evidence suggests that consuming moderate amounts of alcohol is a risk factor for obesity, which is a risk factor for several adverse health outcomes. Recommendations regarding alcohol intake thus should take into account a variety of factors, including baseline body weight, location of body fat, and overall diet.

Whole body and splanchnic metabolic and circulatory effects of glucose during beta-adrenergic receptor inhibition

The aim of the study was to assess the possible contribution of adrenergic mechanisms to the thermogenic and circulatory effects of glucose ingestion. With the use of indirect calorimetry and arterial, pulmonary arterial, and hepatic venous catheterization, whole body and splanchnic oxygen uptake and blood flow were examined in nine propranolol-treated healthy male volunteers before and during 2 h after oral ingestion of 75 g of glucose. The glucose effects were compared with those in nine untreated controls. After propranolol, the glucose-induced rise in splanchnic blood flow was reduced by approximately 60%, and the hepatic venous glucose release to the systemic circulation was significantly delayed. Glucose-induced increments in pulmonary and splanchnic oxygen uptake and cardiac output were similar in the two groups. It is concluded that adrenergic mechanisms contribute to the glucose-induced rise in splanchnic blood flow and thereby probably to the time course for intestinal absorption of nutrients. It is suggested that the magnitude of glucose-induced thermogenesis is independent of adrenergic stimulation.

Energy expenditure, body composition, and disease risk in children and adolescents

Recent methodological advances have led to a tremendous improvement in our ability to measure energy expenditure, body composition and fat distribution in children. The availability of new and improved measurement techniques has greatly enhanced the scope of research studies in children. The key findings from the present review are as follows: total energy expenditure in young children is approximately 25% lower than current recommendations for energy intake and revised recommendations are necessary; reduced energy expenditure, however, does not necessarily explain the greater prevalence of obesity in the population as a whole or in sub-groups at greater risk of obesity; qualitative aspects of physical activity (e.g. time, intensity) may be more important than the energy expenditure of physical activity in the regulation of body composition; for body composition assessment, DXA is emerging as a technique which can substantially improve the accuracy and standardization in children; body fat begins to accumulate in the obese; waist:hip ratio or waist circumference are inadequate markers of intra-abdominal adipose tissue in children and adolescents; finally, the early accumulation of fat in the intra-abdominal region is significantly related to the development of adverse health effects, including dyslipidaemia and glucose intolerance.

Total energy expenditure and the level of physical activity correlate with plasma leptin concentrations in five-year-old children

Leptin, the product of the ob gene, is a hormone secreted by adipocytes that is known to decrease food intake and increase energy expenditure in ob/ob mice. In humans, variants in the OB gene have not been detected and very little is known about the action of leptin on food intake and energy expenditure, although circulating leptin concentrations are positively correlated to body fat stores. The purpose of this study was to assess the relationship between fasting plasma leptin concentrations and energy expenditure in 123 5-yr-old Pima Indian children (67 males/76 females). Body composition was assessed by isotopic water dilution (18O) whereas total energy expenditure (TEE) and resting metabolic rate (RMR) were measured using doubly labeled water and indirect calorimetry, respectively. The physical activity level was calculated as the ratio of TEE:RMR. Plasma leptin concentrations were positively correlated to percent body fat (r = 0.84, P < 0.0001), but were similar in boys and girls after adjusting for percent body fat. Most importantly, we found that, independent of the percentage of body fat, plasma leptin concentrations correlated with TEE (in absolute values, r = 0.37, P < 0.0001, or adjusted for body size r = 0.42; P < 0.0001) and with physical activity level (r = 0.26, P < 0.01), but not RMR. These results suggest that, as in animal models, leptin plays a role in energy expenditure in humans.

Lack of effect of sleep on energy expenditure and physiologic measures in critically ill burn patients

OBJECTIVE

Energy expenditure measurements, performed while patients are in standardized resting conditions, are often used as an indicator of care by which to evaluate the adequacy of nutrition support regimens. Little attention has been directed toward examining potential errors incurred by deriving daily energy needs based on a single 15- to 20-minute measurement. This study was designed to differentiate energy expenditure during periods of sleep (defined as time spent in any of the standard sleep stages) and wakefulness in pediatric burn patients.

DESIGN

Twenty-four-hour indirect calorimetry, polysomnography, and physiologic assessments (mean arterial pressure, heart rate, body temperature, oxygen saturation, and respiratory rate) were conducted simultaneously in 14 patients, who were thermally injured and tracheally intubated, for a total of 45 24-hour intervals.

SUBJECTS

Mean age of the patients was 10.8+/-1.2 years. Mean total body surface area of the injury was 55.7+/-4.7%, and mean full-thickness burn was 48.8+/-6.0%.

STATISTICAL ANALYSES PERFORMED

A nested general linear analysis of variance model was used to evaluate the association between sleep, wakefulness, and energy needs; adjustments were made for postburn day and multiple test runs per patient.

RESULTS

On average, subjects slept 699+/-46 minutes/day. They experienced a large number of awakenings from sleep (mean=53+/-6.3 awakenings per 24 hours). Patients had mean energy expenditure of 2,529+/-396 kcal/day while awake and 2,360+/-291 kcal/day while asleep, and these mean values did not differ significantly. No differences in physiologic measurements during the awake and sleep states were found.

APPLICATIONS

There appears to be little difference in the metabolism of seriously injured burn patients while asleep and while awake. The study deemphasizes the importance of performing indirect calorimetry at rest in critically ill pediatric burn patients, and it supports the extrapolation of daily energy expenditure from a 15- to 20-minute steady-state measurement obtained during either sleep or wakefulness.

Resting energy expenditure in obese African American and Caucasian women

The prevalence of obesity among African American women approaches 50% and greatly exceeds rates for Caucasian women. In addition, black women lose less weight than white during obesity treatment and gain more weight when untreated. This study assessed resting energy expenditure (REE) and body composition in obese white (n = 122) and black (n = 44) women to explore the relationship between biological variables and these observed differences. REE and body composition were assessed by indirect calorimetry and densitometry, respectively, before weight loss. REE was significantly lower in black subjects (1637.6 +/- 236.9 kcal/d) than in white (1731.4 +/- 262.0) (p = 0.04). REE remained significantly lower in blacks than whites after adjusting for body weight (p = 0.02). REE, adjusted for fat-free mass, was also significantly lower in blacks than whites (p < 0.0001), although the overestimation of fat-free mass by densitometry in blacks may have contributed to this finding. There were no differences between the groups in respiratory quotient. These results suggest that a decreased REE may exist in obese black women, and it may be related to the observed differences between black and white women in the prevalence of obesity and in the response to weight loss treatment. These cross-sectional findings await confirmation in longitudinal studies.

Energy expenditure

Although human energy expenditure has been studied for over 100 years, many unanswered questions remain regarding the role that individual components of energy expenditure have in the etiology of obesity. Most techniques for measuring physical activity, the most variable component of TDEE, are less than adequate, and differences in energy metabolism are difficult to detect in a static comparison. When energy expenditure is examined in obese and lean subjects at one point in time, there frequently are no differences in energy expenditure when appropriately normalized. However, when subjects are studied longitudinally or when the system is perturbed (such as overfeeding or exercising), differences can be observed. Using a combination of the techniques available today, each component can be reliably studied, and the role that each has in the development of obesity can be ascertained.

Effects of glucocorticoids on energy metabolism and food intake in humans

The effect of glucocorticoid administration on energy metabolism and food intake was studied in 20 healthy, nondiabetic Caucasian male volunteers [27 +/- 5 (SD) yr, 72 +/- 9 kg, 20 +/- 7% body fat] randomly and blindly assigned to glucocorticoid (methylprednisolone, METH; n = 10) or placebo (PLAC; n = 10) treatment. Each subject was studied twice: during a weight maintenance diet and during ad libitum food intake. Energy metabolism was measured by indirect calorimetry and food intake by an automated food-selection system. Twenty-four-hour urinary norepinephrine excretion (24-h NE) was used as an estimate of sympathetic nervous system activity. During weight maintenance, METH intravenous infusion (125 mg/30 min) increased energy expenditure compared with PLAC, and after 4 days of oral therapy, METH (40 mg/day) decreased 24-h NE and increased energy expenditure compared with PLAC. During ad libitum food intake, after 4 days of METH (40 mg/day) or PLAC oral therapy, both groups increased their energy intake over weight maintenance, but the increase was significantly larger in the METH group compared with the PLAC group (4,554 +/- 1,857 vs. 2,867 +/- 846 kcal/day; P = 0.04). Our data suggest that therapeutic doses of glucocorticoids induce obesity mostly by increasing energy intake, an effect which may be related to the ability of glucocorticoids to act directly or indirectly on the central regulation of appetite.

Decreased ratio of fat to carbohydrate oxidation with increasing age in Pima Indians

BACKGROUND

Some metabolic changes related to age may increase the prevalence of obesity. Previous studies have shown that a low relative metabolic rate and a low ratio of fat to carbohydrate utilization are predictors of body weight gain. However, a possible relationship between age and energy substrate utilization (respiratory quotient; RQ = VCO2/VO2) has not been reported.

OBJECTIVE

To determine whether RQ increases and therefore fat oxidation decreases with age in Pima Indian men, independent of body fat and energy balance.

METHODS

We analyzed longitudinal data collected in seven non-diabetic Pima Indian men (31 +/- 6 years, 167 +/- 8 cm, 111.0 +/- 23.7 kg and 41 +/- 9% fat at baseline) who had repeated measurements of 24-hour RQ 7 years apart. On both admissions, subjects were fed a weight maintenance diet (50% carbohydrate, 30% fat and 20% protein) for 3 days before spending 1 day within a respiratory chamber for measurements of 24-hour energy expenditure, basal metabolic rate, sleeping metabolic rate and 24-hour RQ. Paired t-test was used to determine differences between the first and last measurement of 24-hour RQ. Cross-sectional data in 131 Pima Indian men (28 +/- 9 years, 171 +/- 6 cm, 94.5 +/- 24.4 kg, and 32 +/- 9% fat) were also analyzed to determine the relationship between 24-hour RQ and age. Multiple regression analysis was used to adjust 24-hour RQ for differences in energy balance (intake/expenditure in %) and percent body fat and metabolic rate for differences in body size and composition.

RESULTS

Over a 7-year period, mean unadjusted and adjusted 24-hour RQ increased (p < 0.01). Cross-sectional data analysis showed that both the unadjusted (r = 0.19, p < 0.03) and adjusted (r = 0.19, p < 0.03) 24-hour RQ correlated with increasing age while adjusted BMR (r = -0.21, p < 0.02) correlated inversely with age.

CONCLUSIONS

Despite a higher body fat content, older individuals utilize less fat than their younger counterparts. Reduced fat utilization and decreased BMR with age may both contribute to increasing obesity in older individuals.

Chamber for indirect calorimetry with improved transient response

A chamber for indirect calorimetry has been constructed that utilises previously published general equations for the calculation of respiration. Owing to the large size of the chamber, the changes in gas concentration caused by a subject are very small. Therefore, algorithms are developed for noise suppression and trend identification. Using the exact solution of the equations for steady state, each gas concentration is fitted by a least square method to two connected exponential segments, of variable length, for the preceding 30 min period. Independently of the location of the join between the two segments, the gas concentration and its time derivative are evaluated at -15 min. This process is repeated, and its results are presented once every minute. As proven by gas injection tests, this procedure gives an instantaneous response to a single change in respiration, a correct averaging of repeated changes in respiration with periods of less than 15 min and noise suppression. It is concluded that this chamber is useful not only for traditional 24 h energy expenditure measurements, but also for experiments requiring rapid responses.

Twenty-four-hour energy and nutrient balance in weight stable postobese patients after biliopancreatic diversion

To better understand the long-term weight stability of postobese patients who underwent biliopancreatic diversion (BPD), we studied 24-h energy and nutrient balance in eight women at least 3 yr after surgery (PO) and compared the results to those obtained in eight normal never-obese control women (C), matched by age and weight. Body composition was measured by dual-energy x-ray absorptiometry (DXA). All the patients were on an ad libitum diet; 24-h energy and nutrient intake were measured on the experimental day. Twenty-four-hour energy expenditure (EE) and 24-h nutrient oxidation rates were measured in a respiratory chamber, and energy and nutrient balances were calculated after correcting for 24-h fecal nutrient loss. No differences in body composition were found between PO and C. PO had a higher gross energy intake than C (10.6 +/- 3.4 vs. 8.0 +/- 2.2 MJ/d; p < 0.05); however, due to the higher energy fecal loss in PO as compared to C (2.4 +/- 1.3 vs. 0.09 +/- 0.01 MJ/day; p < 0.01), 24-h metabolizable energy intake (MEJ) was not different in the two groups. The energy fecal loss in the PO patients was mostly in the form of lipid. EE at 24 h was not different in PO as compared to C. Therefore energy balance, computed as the difference between 24-h MEI and 24-h EE, was similar in the two groups. Respiratory quotient was significantly higher in PO than in C (1.00 +/- 0.08 vs. 0.83 +/- 0.03; p < 0.01). Carbohydrate (-135 +/- 37 g/d in PO vs. 63 +/- 23 g/d in C; p < 0.001), and lipid (48 +/- 14 g/d in PO vs. -23 +/- 6 g/d in C; p < 0.001) balances were different in the two groups. We conclude that chronic lipid malabsorption was the main metabolic abnormality explaining the achievement of energy balance in postobese subjects after biliopancreatic diversion. A chronic reduction of lipid absorption seems to play a key role in the long-term weight stability of this group of postobese subjects.

Physical activity, nutrition, and chronic disease

Epidemiologic, animal, clinical, and metabolic studies demonstrate the independent roles of physical activity and nutrition in the prevention and treatment of several chronic diseases. Fewer data are available to describe the synergistic effects of exercise and diet, and questions remain as to whether and how these two lifestyle factors work together to promote health and prevent disease. This paper briefly reviews many of the known effects of physical activity and nutrition on the prevention and treatment of coronary heart disease, non-insulin-dependent diabetes mellitus, obesity, and osteoporosis as well as how exercise and diet may work together. A discussion of how to increase physical activity levels and how to improve dietary intake also is included. Finally, current exercise and dietary recommendations are summarized, as are directions for future research.

Activity level and risk of overweight in male health professionals

OBJECTIVES

This study undertook to examine relationships between nonsedentary activity level, time spent watching television (TV)/videocassette recorder (VCR), and risk of overweight among men.

METHODS

Men participating in the Health Professionals Follow-Up Study were mailed surveys. Cross-sectional analyses examined the prevalence and odds of being overweight, prospective analyses determined cumulative incidence rates and relative risks of becoming overweight over 2 years of follow-up.

RESULTS

Cross-sectionally, odds of being overweight were 50% (95% confidence interval [CI] = 45%; 55%) lower for men in the highest quintile of nonsedentary activity level when compared with men in the lowest quintile. Among men watching 41 or more hours of TV/VCR per week, the odds of being overweight were 406 (95% CI = 2.67, 6.17) times greater than those for men watching no more than 1 hour per week. Prospectively, higher levels is of nonsedentary activity and lower levels of TV/VCR viewing were independently associated with lower relative risks for becoming overweight between survey years.

CONCLUSIONS

Both a lack of nonsedentary activity and time spent watching TV/VCR contribute to the development of overweight in men. Sedentary and nonsedentary activities represent separate domains, each with independent risks for overweight.

Thyroid hormone control of thermogenesis and energy balance

The mechanisms whereby thyroid hormone increases heat production have been analyzed with emphasis in more recent developments. Thyroid hormone increases obligatory thermogenesis as a result of the stimulation of numerous metabolic pathways involved in development, remodeling, and delivery of energy to the tissues. In addition, thyroid hormone may specifically stimulate some thermogenic mechanisms selected during evolution of homeotherms (e.g., Na/K-ATPase, Ca2+ cycling in muscle). Thyroid hormone also plays an essential role in facultative thermogenesis interacting with the sympathetic nervous system (SNS) at various levels. Peripherally, thyroid hormone potentiates the effects of the SNS at the level of the adrenergic receptor and adenylyl cyclase complex as well as distal from this point. Synergistic interactions between T3 and cAMP on the regulation of gene expression have been described. Brown adipose tissue (BAT) T4-5'-deiodinase plays a central role in controlling heat production. When this enzyme is stimulated by norepinephrine in the euthyroid and hypothyroid condition, it provides high concentrations of T3 to BAT; inhibition by T4 in hyperthyroidism may limit brown fat thermogenic responses. Also, thyrotoxicosis uniquely reduces the expression of beta 3-adrenergic receptors in brown adipose tissue, and the increased obligatory thermogenesis of this condition, via afferent neural pathways, may reduce the hypothalamic stimulation of brown fat, providing additional mechanisms to limit brown adipose tissue thermogenesis in hyperthyroidism.

Daily energy metabolism in patients with type 1 diabetes mellitus

OBJECTIVE

We evaluated the daily energy balance and main substrate utilization in Type 1 insulin dependent diabetic patients and healthy volunteers.

METHODS

Ten patients with Type 1 diabetes mellitus and eight healthy volunteers were studied. Diabetic patients were well controlled under intensive insulin treatment (0.6 UI/kg body weight, HbA1c = 5.5 +/- 0.7%). During the 30 hours each subject spent in the respiration chamber VO2, VCO2, respiratory quotient, daily energy intake, 24-hour, day-time, night-time and basal energy expenditure as well as energy expenditure during exercise (at 40% maximal exercise capacity), main substrate oxidation (carbohydrates, lipids and proteins) and overall diet-induced thermogenesis, were measured. The results were corrected for 24-hour urinary nitrogen loss.

RESULTS

Diet-induced thermogenesis, expressed as percent of energy intake, was found to be significantly lower in diabetic patients than in control subjects (6.69 +/- 1.29% vs 11.8 +/- 4.71% of energy intake, p < 0.05). A negative correlation was found between diet-induced thermogenesis and daily average glycemia for diabetic patients (r = -0.65, p < 0.01). Energy expenditure during exercise, calculated in terms of net work efficiency, was not different between the two groups.

CONCLUSIONS

In conclusion, since diet-induced thermogenesis is highly correlated with the theoretical cost of glucose storage and since no difference was found in carbohydrate oxidation, glucose storage in diabetic patients is probably reduced when hyperglycemia occurs. Diabetic patients in good metabolic control are able to perform mild exercise with a work efficiency very similar to that of control subjects.

Obesity in children: recent advances in energy metabolism and body composition

In this paper we review recent advances in energy metabolism and body composition studies in prepubescent children and the relationship to childhood obesity. Our review on energy expenditure focusses on studies of total energy expenditure using doubly labeled water, the role of energy expenditure in the development of obesity, and the determinants of resting energy expenditure in children. The relatively few studies that have examined the regulation of energy and macronutrient intake in children are also reviewed. In terms of body composition, we focus on recent methodological studies that have developed existing techniques for application to the pediatric population, including dual energy X-ray absorptiometry and bioelectrical resistance. Lastly, we review existing information relating to measurement and alteration of body fat distribution in children.

Changes in energy expenditure resulting from altered body weight

BACKGROUND

No current treatment for obesity reliably sustains weight loss, perhaps because compensatory metabolic processes resist the maintenance of the altered body weight. We examined the effects of experimental perturbations of body weight on energy expenditure to determine whether they lead to metabolic changes and whether obese subjects and those who have never been obese respond similarly.

METHODS

We repeatedly measured 24-hour total energy expenditure, resting and nonresting energy expenditure, and the thermic effect of feeding in 18 obese subjects and 23 subjects who had never been obese. The subjects were studied at their usual body weight and after losing 10 to 20 percent of their body weight by underfeeding or gaining 10 percent by overfeeding.

RESULTS

Maintenance of a body weight at a level 10 percent or more below the initial weight was associated with a mean (+/- SD) reduction in total energy expenditure of 6 +/- 3 kcal per kilogram of fat-free mass per day in the subjects who had never been obese (P < 0.001) and 8 +/- 5 kcal per kilogram per day in the obese subjects (P < 0.001). Resting energy expenditure and nonresting energy expenditure each decreased 3 to 4 kcal per kilogram of fat-free mass per day in both groups of subjects. Maintenance of body weight at a level 10 percent above the usual weight was associated with an increase in total energy expenditure of 9 +/- 7 kcal per kilogram of fat-free mass per day in the subjects who had never been obese (P < 0.001) and 8 +/- 4 kcal per kilogram per day in the obese subjects (P < 0.001). The thermic effect of feeding and nonresting energy expenditure increased by approximately 1 to 2 and 8 to 9 kcal per kilogram of fat-free mass per day, respectively, after weight gain. These changes in energy expenditure were not related to the degree of adiposity or the sex of the subjects.

CONCLUSIONS

Maintenance of a reduced or elevated body weight is associated with compensatory changes in energy expenditure, which oppose the maintenance of a body weight that is different from the usual weight. These compensatory changes may account for the poor long-term efficacy of treatments for obesity.

Physical activity, total energy expenditure, and food intake in grossly obese and normal weight women

The doubly labeled water method was used to measure average daily total energy expenditure (TEE) in 10 healthy normal weight women classified as unrestrained eaters and in 10 grossly obese women. The body mass index was 20.0 +/- 1.3 kg/m2 in the control group and 37.4 +/- 8.1 kg/m2 for the obese group. TEE was measured over a 2-week period. TEE was 2,357 +/- 504 kcal/day for the controls and 3,708 +/- 367 kcal/day for the obese group during a cognitive-behavioral treatment.

Relationship between sleep stages and metabolic rate in humans

Differences in sleeping metabolic rate (SMR) among subjects may be related to different levels of energy expenditure associated with sleep stages. The relationship between energy expenditure and sleep stages was investigated overnight in 29 subjects (14 Caucasians and 15 Pima Indians, 18 males and 11 females; mean +/- SD, 31 +/- 7 yr, 83 +/- 26 kg, 27 +/- 11% fat). Sleep stages were determined by electroencephalogram recording, whereas energy expenditure was measured in a 1,000-liter Plexiglas sleep box constructed around a bed as a fast-response open-circuit indirect calorimeter. Eighty-five percent of the interindividual variability in SMR was explained by differences in fat-free mass, fat mass, age, sex, and race (r2 = 0.85). The intra-individual variance in SMR over time was related to sleep stages and to clock time. Within subjects, SMR in stage 3 was significantly lower than in stage 2 (-39 +/- 18 kcal/day; P < 0.05) and rapid eye movement sleep (-51 +/- 23 kcal/day; P < 0.05). Also, sleep stages were associated with different respiratory quotients. Because sleep stages are associated with only small differences in energy metabolism, our results suggest that sleep stages play a minor role in the variance of SMR among subjects. However, the duration of sleep may contribute to the variability of 24-h energy expenditure.

Determinants of resting energy expenditure in young children

Resting energy expenditure (REE) in adults is influenced by fat-free mass (FFM) and fat mass (FM), and is significantly higher in men than in women. There are limited data, however, on the physiologic determinants of REE in children. We therefore measured REE in 113 prepubertal children (39 white girls, 41 white boys, 21 Mohawk girls, and 12 Mohawk boys), 3.9 to 7.8 years of age, representing a wide range of body weight (14.7 to 34.0 kg), height (0.97 to 1.30 m), FFM (10.3 to 25.0 kg), and FM (1.7 to 13.7 kg; 9.4% to 40.3%). The REE was measured in duplicate by indirect calorimetry (range, 830 to 1405 kcal/day) while the children were in a postprandial state and viewing a cartoon film. The FM and FFM values were determined by bioelectrical resistance by means of the Kushner equation. In stepwise regression analysis, the combination of FFM (p < 0.001; partial r = 0.77), sex (p = 0.001; partial r = 0.12), and FM (p = 0.01; partial r = 0.16) explained 63% of the variation in REE. The regression coefficients were 31.9 kcal/kg FFM, 53 kcal for boys, 0 for girls, and 13 kcal/kg FM. Mohawk background, age, fat distribution, heart rate, and physical activity were not independently associated with REE. After REE was adjusted for the aforementioned significant factors, there were no significant correlations with parental factors (body composition, physical activity, age, and REE) other than normalized maternal REE (r = 0.19; p = 0.05). We conclude that the effects of FFM, sex, and FM on REE in children are similar to those in adults. The higher REE in young boys suggests that the previously reported higher REE in adult men cannot be explained entirely by differences in sex hormones. Finally, our data do not support the hypothesis that REE in children is negatively influenced by obesity in children or in parents.

Energy and macronutrient metabolism

In general, obesity is a state of high energy stores, high energy intake, and high energy expenditure. The high energy expenditure is largely due to the increased fat-free mass. The failure to find a positive relationship between reported energy intake and body size reflects a greater under-reporting of calorie intake among obese individuals. Obesity, therefore, develops as a consequence of a chronic imbalance between intake and expenditure, although the cause of this is not apparent from the energy balance equation. However, this equation can be dissected into its component nutrient balance equations because net de novo lipogenesis is negligible in free-living humans. Fat calories are handled very differently from non-fat calories. Non-fat nutrient oxidation rates rise and fall to match the fluctuations in non-fat intake so that non-fat calorie balance is actively maintained. In contrast, changes in fat intake do not acutely affect fat oxidation but are matched by changes in storage. Therefore, within the fat balance equation there is ample scope for a chronic imbalance between fat intake and oxidation. Also, there is some evidence that carbohydrate balance may be an important signal for hunger and satiety. These concepts imply that, under free-living, ad libitum eating conditions, changes in nutrient intake composition (e.g. an increased proportion of fat in the diet) or changes in nutrient oxidation composition (e.g. a decrease in the proportion of fat oxidized) will lead to body weight change (in these cases, to weight gain). Considering obesity as a consequence of normal physiology (with its normal variation between individuals) in a 'pathological' environment (high fat diet, low exercise) offers an important perspective for explaining the interpopulation and interindividual differences in obesity and for formulating treatment and prevention options. Low energy expenditure (relative to body size), high respiratory quotient and insulin sensitivity have been shown to be predictors of weight gain, although upon gaining weight these metabolic factors tend to 'normalize'. Metabolic responses to underfeeding or overfeeding are largely predictable from the changes in calorie intake and changes in body composition, but some adaptive changes may occur.

Columbia respiratory-chamber indirect calorimeter: a new approach to air-flow modelling

A new air-flow modelling approach for respiratory-chamber indirect calorimetry is introduced. Based on thermodynamic theory, differential equations describing the dynamics of the calorimeter are derived. These equations are then developed into a linear state space model that can be conceptualized as a modern control system. Furthermore, both the system/output noises and input/output delays are considered in the model in the context of real applications. Finally, system accuracy is analysed so that the parameters in the calorimeter can be selected to minimise the error in estimating energy expenditure in humans.

Menopausal changes in body composition and energy expenditure

Adult American women as a group tend to gain weight with age, and many women report that their weight gain started around the time of their menopause. Moreover, as women age, there are changes in body composition that include losses in bone mineral and body cell mass, and increases in total body fat, visceral fat, and extracellular fluid. It appears as if these body composition changes begin or accelerate during the menopausal years. The importance of weight gain and changes in body composition are their associations with an increased risk of developing some malignancies, cardiovascular disease, osteoporosis, and several other clinical conditions. This overview describes selected studies of menopause and aging-associated weight gain, changes in body composition, and alterations of energy expenditure in women. Gaps in the present understanding of these changes are highlighted, and an emphasis is placed on new research methodologies for investigating body composition and energy expenditure in vivo. A concluding section of the report summarizes areas in need of future investigation.

Whole-body energy metabolism and skeletal muscle biochemical characteristics

A low metabolic rate for a given body size and a low fat versus carbohydrate oxidation ratio are known risk factors for body weight gain, but the underlying biological mechanisms are poorly understood. Twenty-four-hour energy expenditure (24EE), sleeping metabolic rate (SMR), 24-hour respiratory quotient (24RQ), and forearm oxygen uptake were compared with respect to the proportion of skeletal muscle fiber types and the enzyme activities of the vastus lateralis in 14 subjects (seven men and seven women aged 30 +/- 6 years [mean +/- SD], 79.1 +/- 17.3 kg, 22% +/- 7% body fat). The following enzymes were chosen to represent the major energy-generating pathways: lactate dehydrogenase (LDH) and phosphofructokinase (PFK) for glycolysis; citrate synthase (CS) and beta-hydroxyacl-coenzyme A dehydrogenase (beta-OAC) for oxidation; and creatine kinase (CK) and adenylokinase (AK) for high-energy phosphate metabolism. Forearm resting oxygen uptake adjusted for muscle size correlated positively with the proportion of fast-twitch muscle fibers (IIa: r = .55, P = .04; IIb: r = .51, P = .06) and inversely with the proportion of slow oxidative fibers (I: r = -.77, P = .001). 24EE and SMR adjusted for differences in fat-free mass, fat mass, sex, and age correlated with PFK activity (r = .56, P = .04 and r = .69, P = .007, respectively). 24RQ correlated negatively with beta-OAC activity (r = -.75, P = .002). Our findings suggest that differences in muscle biochemistry account for part of the interindividual variability in muscle oxygen uptake and whole-body energy metabolism, ie, metabolic rate and substrate oxidation.

Diminished brain glucose metabolism is a significant determinant for falling rates of systemic glucose utilization during sleep in normal humans

Systemic glucose utilization declines during sleep in man. We tested the hypothesis that this decline in utilization is largely accounted for by reduced brain glucose metabolism. 10 normal subjects underwent internal jugular and radial artery cannulation to determine cerebral blood flow by N2O equilibrium technique and to quantitate cross-brain glucose and oxygen differences before and every 3 h during sleep. Sleep stage was graded by continuous electroencephalogram, and systemic glucose turnover was estimated by isotope dilution. Brain glucose metabolism fell from 33.6 +/- 2.2 mumol/100 g per min (mean +/- SE) before sleep (2300 h) to a mean nadir of 24.3 +/- 1.1 mumol/100 g per min at 0300 h during sleep (P = 0.001). Corresponding rates of systemic glucose utilization fell from 13.2 +/- 0.8 to 11.0 +/- 0.5 mumol/kg per min (P = 0.003). Diminished brain glucose metabolism was the product of a reduced arteriovenous glucose difference, 0.643 +/- 0.024 to 0.546 +/- 0.020 mmol/liter (P = 0.002), and cerebral blood flow, 50.3 +/- 2.8 to 44.6 +/- 1.4 cc/100 g per min (P = 0.021). Brain oxygen metabolism fell commensurately from 153.4 +/- 11.8 to 128.0 +/- 8.4 mumol/100 g per min (P = 0.045). The observed reduction in brain metabolism occurred independent of stage of central nervous system electrical activity (electroencephalographic data), and was more closely linked to duration of sleep. We conclude that a decline in brain glucose metabolism is a significant determinant of falling rates of systemic glucose utilization during sleep.

Physical activity and obesity

Obesity is a major public health problem. Secular increases in the prevalence of obesity appear to be paralleled by decreases in physical activity. Although physical activity and weight are associated, the exact nature of the relationship remains uncertain. Research strongly suggests that exercise is a critical component of any program for weight control and health improvement. Potential mechanisms linking exercise and weight are discussed. For some persons, the health improvement derived from increased activity may not depend on weight loss. Modest levels of activity may be sufficient to achieve both the weight and health benefits of exercise.

Impact of regional and total body composition and hormones on resting energy expenditure in overweight postmenopausal women

The independent impact of regional and total body composition and sex and thyroid hormone levels on resting energy expenditure (REE) was assessed in 121 healthy, overweight (body mass index [BMI], 25 to 42 kg/m2), postmenopausal women (aged 49 to 58 years). REE was measured by indirect calorimetry with a ventilated hood, and the total, trunk, and peripheral body composition by dual-energy x-ray absorptiometry (DXA). Sex and thyroid hormone levels were also measured. REE correlated significantly (P < .05) better with trunk lean tissue mass ([LTM] r = .61) than with total-body (r = .53) or peripheral LTM (r = .30). Trunk LTM (R2 = .37), total-body fat tissue mass ([FTM] R2 = .04), androstenedione (R2 = .03), and total triiodothyronine ([T3] R2 = .02) were all significantly independently associated with REE. Together they explained 46% (model R2) of the interindividual variation in REE, with a standard error of estimate (SEE) of 549 kJ/d. We conclude that the interindividual variation in REE is explained mainly by differences in the visceral component of LTM, with additional minor information from the total-body FTM, androstenedione, and T3.

Reduced sympathetic nervous activity. A potential mechanism predisposing to body weight gain

The sympathetic nervous system is recognized to play a role in the etiology of animal and possibly human obesity through its impact on energy expenditure and/or food intake. We, therefore, measured fasting muscle sympathetic nerve activity (MSNA) in the peroneal nerve and its relationship with energy expenditure and body composition in 25 relatively lean Pima Indian males (means +/- SD; 26 +/- 6 yr, 82 +/- 19 kg, 28 +/- 10% body fat) and 19 Caucasian males (29 +/- 5 yr, 81 +/- 13 kg, 24 +/- 9% body fat). 24-h energy expenditure, sleeping metabolic rate, and resting metabolic rate were measured in a respiratory chamber, whereas body composition was estimated by hydrodensitometry. Pima Indians had lower MSNA than Caucasians (23 +/- 6 vs 33 +/- 10 bursts/min, P = 0.0007). MSNA was significantly related to percent body fat in Caucasians (r = 0.55, P = 0.01) but not in Pimas. MSNA also correlated with energy expenditure adjusted for fat-free mass, fat mass, and age in Caucasians (r = 0.51, P = 0.03; r = 0.54, P = 0.02; and r = 0.53, P = 0.02 for adjusted 24-h energy expenditure, sleeping metabolic rate, and resting metabolic rate, respectively) but not in Pima Indians. In conclusion, the activity of the sympathetic nervous system is a determinant of energy expenditure in Caucasians. Individuals with low resting MSNA may be at risk for body weight gain resulting from a lower metabolic rate. A low resting MSNA and the lack of impact of MSNA on metabolic rate might play a role in the etiology of obesity in Pima Indians.

Assessment of body composition with use of dual-energy x-ray absorptiometry: evaluation and comparison with other methods

Dual-energy x-ray absorptiometry (DEXA) is a relatively new method of assessing body composition in humans. In the current study, DEXA was analyzed for accuracy and precision by using both anthropomorphic phantoms and a combination of body composition techniques in humans. Satisfactory precision for measurement of total body fat, fat-free mass, and total body bone mineral could be demonstrated in vivo and in vitro. Predictions of lean body mass in humans on the basis of DEXA, total body water, and total body potassium were significantly different. The results of multiple regression analysis suggested that a component of total body water was related to body potassium, and another component was predicted by body fat. In addition, extracellular fluid volume, as measured by the bromide space technique, was significantly associated with both fat-free mass and fat mass as measured by DEXA. These findings have implications for the interpretation of body composition data in humans.

Resting energy expenditure in the obese: a cross-validation and comparison of prediction equations

OBJECTIVE

To examine the accuracy and precision of 12 equations or tables for predicting resting metabolic rate (RMR) in obese persons.

DESIGN

Observational (correlational) study.

SETTING

Obesity Research Center, St Luke's/Roosevelt Hospital, New York, NY.

SUBJECTS/SAMPLES

One hundred twenty-six (73 women, 53 men) healthy, obese subjects recruited through the Obesity Research Center's Weight Control Unit.

MEASURES

RMR by indirect calorimetry. Weight and height were measured to the nearest 0.1 kg and to the nearest 1 cm.

STATISTICAL ANALYSES PERFORMED

Bivariate regression of predicted RMR on measured RMR; paired t tests for the difference between means of predicted RMR and measured RMR.

RESULTS

Of the 12 prediction equations, 6 had intercepts or slopes that were significantly different from 0 and 1, respectively. With two exceptions, the equations accounted for between 56% and 63% of the variance in measured RMR. The Robertson and Reid (1952) equation and the Fleisch (1951) equation performed best with our obese sample.

APPLICATIONS/CONCLUSIONS

The Robertson and Reid (1952) and the Fleisch (1951) equations are recommended for clinical use with obese patients.

A practical equation to predict resting metabolic rate in older men

The accuracy of previous equations for predicting resting metabolic rate (RMR) in healthy older men is questionable because they are based on limited sample sizes and the absence of cross-validation procedures. The purposes of this study were to (1) examine biological predictors of RMR in healthy older men; (2) develop a practical equation to predict RMR from easily measured variables and examine its accuracy using cross-validation procedures; and (3) test the validity of existing equations in the literature to predict RMR in older men by comparison with measured RMR values. RMR, body composition, anthropometric measurements, leisure time activity (LTA), maximal aerobic power (VO2max), energy intake, and plasma thyroid hormone levels were determined in 89 healthy older men aged 50 to 78 years. Stepwise regression analysis showed that RMR was best predicted by fat-free weight ([FFW] R2 = 85%), free 3,5,3'-triiodothyronine (T3) level (R2 = 1%), and VO2max (R2 = 1%); these variables predicted RMR with a residual error of +/- 30 kcal/d. A practical equation was developed in a randomly selected subsample (N = 61) using easily measured variables as potential predictors, and was successfully cross-validated in a random subsample of older men (N = 28). The pooled equation to predict RMR is as follows: RMR (in kilocalories per day) = 9.7 (weight in kilograms) - 6.1 (chest skinfold thickness in millimeters) - 1.8 (age in years) + 0.1 (leisure time activity [LTA] in kilocalories per day) + 1,060. These variables accounted for 76% (R2) of the variation, and predicted RMR with a residual error of +/- 42 kcal/d.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between skeletal muscle lipoprotein lipase activity and 24-hour macronutrient oxidation

A low ratio of whole-body 24-h fat/carbohydrate (CHO) oxidation has been shown to be a predictor of subsequent body weight gain. We tested the hypothesis that the variability of this ratio may be related to differences in skeletal muscle metabolism. Since lipoprotein lipase (LPL) plays a pivotal role in partitioning lipoprotein-borne triglycerides to adipose (storage) and skeletal muscle (mostly oxidation), we postulated that a low ratio of fat/CHO oxidation was associated with a low skeletal muscle LPL (SMLPL) activity. As an index of substrate oxidation, 24-h RQ was measured under sedentary and eucaloric conditions in 16 healthy nondiabetic Pima males. During a 6-h euglycemic, hyperinsulinemic clamp, muscle biopsies were obtained at baseline, 3, and 6 h. Heparin-elutable SMLPL activity was 2.92 +/- 0.56 nmol free fatty acids/g.min (mean +/- SD) at baseline, was unchanged (2.91 +/- 0.51) at the third hour, and increased significantly (P < 0.05) to 3.13 +/- 0.57 at the sixth hour of the clamp. The mean (of baseline and 3-h) SMLPL activity correlated inversely with 24-h RQ (r = 0.57, P < 0.03) but not with body size, body composition, or insulin-mediated glucose uptake. Since SMLPL activity is related to the ratio of whole body fat/CHO oxidation rate, a decreased muscle LPL activity may, therefore, predispose to obesity.

Norepinephrine turnover and energy expenditure in Pima Indian and white men

There is growing evidence of the involvement of sympathetic nervous system (SNS) activity in determining metabolic rate. Whole-body plasma norepinephrine turnover and its relationship to resting metabolic rate (RMR) and 24-hour energy expenditure (24EE) were compared in 14 Pima Indian men (25 +/- 4 years, 96 +/- 33 kg, 25% +/- 9% fat) and nine white men (25 +/- 3 years, 88 +/- 43 kg, 17% +/- 13% fat). Plasma norepinephrine turnover rate correlated strongly with body surface area (r = .76 and .54 for clearance and appearance, respectively) and fat-free mass (r = .74 and .52, respectively). However, independent of body size, there was no difference in either norepinephrine clearance or appearance rates between Pima Indian and white men. Norepinephrine appearance rate correlated positively with absolute values of 24EE and RMR, but not when adjusted for differences in body surface area or fat-free mass. However, norepinephrine appearance rate adjusted for differences in body size correlated with spontaneous physical activity. The results indicate that Pima Indian and white men have similar plasma norepinephrine appearance rates, but Pima Indians tend to be more resistant to beta-adrenergic stimulation. Although energy expenditure and SNS activity were not directly related, a higher SNS tone may either promote or reflect elevated levels of spontaneous physical activity and therefore influence both energy balance and body composition.

Variation in total energy expenditure in young healthy free-living men

Interindividual and intraindividual variation in total energy expenditure (TEE) were examined in 17 healthy, free-living men (weight, 56.4 to 82.4 kg; age, 18 to 30 years). TEE over 14 days, resting metabolic rate (RMR), and body composition were measured two or three times during 77 days of fixed caloric intake using doubly labeled water, respiratory gas analysis, and isotope dilution, respectively. When individual data were averaged, TEE was most significantly related to fat-free mass ([FFM] r = .73, P = .001), body mass (r = .70, P = .002), and RMR (r = .63, P = .006). After adjusting TEE for BM, a significant inverse relation with age was found (partial r = -.52, P = .032). Stepwise regression analysis showed that 69% of individual variation in TEE was explained by BM, age, and fasting respiratory exchange ratio (RER). TEE/RMR averaged 1.73 +/- 0.25 (range, 1.38 to 2.32), and was independent of age and body composition. In 10 subjects in whom triplicate observations of TEE were performed, the average experimental variation for TEE was +/- 11.9% (range, 6.1% to 19.6%) compared with a theoretical estimate of precision of +/- 5.9% based on the reported isotope dose and analytical uncertainty. The difference between theoretical estimates of precision and observed experimental variation suggests that inherent random variation in free-living TEE is +/- 10% (ie, square root of 12(2)-6(2)) in subjects maintained on fixed caloric intake. We conclude that in young free living men (1) BM, age, and RER are important determinants of TEE; and (2) intraindividual variation in TEE is approximately +/- 10% due to fluctuations in physical activity levels within individuals over time.

A practical equation to predict resting metabolic rate in older females

OBJECTIVE

To develop a practical and accurate age-specific equation for predicting resting metabolic rate (RMR) in older women and, thereafter, to cross-validate existing equations for predicting RMR in older females.

DESIGN

Cross-sectional validation study.

SETTING

General Clinical Research Center.

PARTICIPANTS

A convenience sample of 75 healthy older women (age 50-81) free of significant cardiovascular or any other non-cardiac disease that may affect cardiovascular function or metabolic rate.

MEASUREMENTS

All 75 volunteers were characterized for resting metabolic rate (RMR), body composition, anthropometrics, physical activity, and energy intake.

RESULTS

A practical equation for predicting RMR in older women using easily measured variables was: [RMR (kcal/d) = 7.8 (weight,kg) + 4.7 (standing height, cm) -39.5 (menopausal status; 1-3) + 143.5]. These variables accounted for 59% (R2) of the variation in RMR and predicted RMR within +/- 66 kcal/d. When five previously published equations were applied to our sample of older women to predict RMR, individual predicted values deviated by -31% to 20% from the measured value.

CONCLUSION

We offer a practical equation to predict RMR in healthy older women based on a measure of body weight, standing height, and menopausal status.