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Objective: To examine characteristics of craved foods in relation to dietary energy restriction (ER) with high (HG) and low glycemic load (LG) diets., Design: Assessments of food cravings before and during a randomized controlled trial of HG and LG diets provided for 6 months., Subjects: Thirty-two healthy, overweight women aged 20-42 years., Measurements: Self-reported food cravings and dietary intake, body weight, weight history and measures of eating behaviors., Results: Foods craved at baseline were more than twice as high in energy density as the habitual diet (3.7+/-1.5 vs 1.7+/-0.3 kcal/g; P<0.001), and on average were lower in protein (P<0.001) and fiber (P<0.001) and higher in fat (P=0.002). There were no statistically significant changes in nutritional characteristics of craved foods after 6 months of ER. There was a significant relationship between reported portion size of craved food consumed at baseline and lifetime high body mass index (r=0.49, P=0.005). Additionally, there was a significant association between susceptibility to hunger and craving frequency at baseline, and there were significant relationships between hunger score, craving frequency, strength and percentage of time that cravings are given in to after 6 months of ER. In multiple regression models, subjects who lost a greater percentage of weight craved higher energy-dense foods at month 6 of ER, but also reported giving in to food cravings less frequently (adjusted R (2)=0.31, P=0.009)., Conclusion: High energy density and fat content, and low protein and fiber contents were identifying characteristics of craved foods. The relationships between craving variables and hunger score suggest that the relative influence of hunger susceptibility on cravings may be important before and especially after ER. Portion size of craved foods and frequency of giving in to food cravings appear to be important areas for focus in lifestyle modification programs for long-term weight loss.

Objective: To examine total energy expenditure (TEE) in relation to occupation and reported leisure time activities in free-living Chinese adults, and to determine whether measured TEE values differ from current international dietary energy recommendations., Setting and Subjects: Seventy three weight-maintaining adults aged 35-49 y, leading unrestricted lives in urban Beijing, with a wide variety of occupations., Design and Methods: A cross-sectional study in which TEE was determined by doubly labeled water, body composition by deuterium oxide ((2)H(2)O) dilution, resting energy expenditure (pREE) by prediction equations, and occupational and leisure time activities by questionnaire., Results: For men and women respectively, TEE averaged 12.10+/-0.32 and 9.53+/-0.23 MJ/day (P<0.001), and physical activity level (PAL=TEE/pREE) was 1.77+/-0.04 and 1.66+/-0.02 (P<0.05). Fat-free mass (FFM) was the single best predictor of TEE (adjusted r(2)=0.71, P<0.001). Occupational category (light, moderate and heavy) further predicted TEE, independent of FFM (adjusted multiple r(2)=0.82, P<0.001). Both TEE adjusted for weight and PAL increased with occupational category. Measured TEE was slightly but significantly higher than the 1985 FAO/WHO/UNU estimates for women with light occupations, but did not differ from estimates for men with light occupations, or for adults with moderate or heavy occupations., Conclusion: Level of occupational activity, but not duration or type of leisure activity, significantly predicted TEE in free-living urban Chinese adults. Current energy requirement recommendations slightly underestimated the energy needs of women with light occupations but were accurate for men and women with moderate and heavy occupations., Sponsorship: NIH grants DK53404 and F32-DK09747.

Objective: Restrained eating is a common dietary practice among individuals who are attempting to prevent weight gain, but little is known about differences in energy physiology and regulation between restrained and unrestrained eaters. We investigated this issue in non-obese free-living postmenopausal women classified as long-term restrained (n=26) or unrestrained (n=34) eaters group matched for body mass index (BMI)., Measurements: Measurements were made of total energy expenditure (TEE), resting energy expenditure (REE), body composition, reported leisure time activity, maximal aerobic capacity (VO2max) and weight change during the study period. In addition, physical activity level (PAL) and nonexercise activity thermogenesis (NEAT) were calculated from measured variables., Results: There were no significant differences between the groups in body composition, weight change, aerobic capacity or total leisure time activity. Relationships between fat-free mass (FFM) and both REE and TEE, and the relationship between work load and energy expenditure in the test of maximal oxygen consumption, were also not different between groups. However, restrained eaters had a significantly lower PAL (equal to TEE/REE, 1.72+/-0.04 vs 1.84+/-0.04, P<0.05). In addition, in multiple regression models predicting NEAT, NEAT was significantly lower in restrained eaters than unrestrained eaters and there was a positive relationship between NEAT and weight change in unrestrained eaters but no relationship in restrained eaters (P<0.05)., Conclusions: In contrast to a previous report, we found no significant difference in TEE between restrained and unrestrained eaters. PAL was slightly lower in restrained eaters, apparently due to reduced NEAT, and restrained eaters also lacked the positive association between NEAT and body weight change seen in unrestrained eaters. This latter finding, if confirmed in future studies, could help explain an increased susceptibility of restrained eaters to weight gain., Sponsorship: NIH grants AG12829, DK46124 and T32AG00209, and US Cooperative Agreement number 58-1950-9-001.

Dietary energy density (ED) has been suggested as an important determinant of energy intake and, therefore, energy regulation. This review summarizes published studies on the effects of dietary ED on hunger, satiety, energy intake, and body weight in healthy individuals, and compares the relative effects of ED manipulated by dietary fat only, fat and fiber, water, and type of sweetener. In short-term studies, consumption of low-ED foods promotes satiety, reduces hunger, and decreases energy intake with no marked differences between different dietary manipulations used to change ED. In addition, low-ED diets promote moderate weight loss in long-term studies. In studies lasting longer than 6 months, weight loss was more than three times as great in individuals consuming diets both low in fat and high in fiber compared with diets only low in fat (-3.4 kg versus -1.0 kg). Combined, these studies suggest that diets low in fat and high in fiber may be the most effective low-ED diets for promoting weight loss. Further research is needed on the effects of dietary ED by changing water or sweetener content.

The effect of aging on energy regulation remains controversial. We compared the effects of underfeeding on changes in energy expenditure and respiratory quotient in young normal weight men and women [YNW, age 25.7 +/- 3.2 y(SD), body mass index (BMI) 23.1 +/- 1.6 kg/m(2)], young overweight men and women (YOW, age 26.1 +/- 3.5 y, BMI 27.7 +/- 2.1 kg/m(2)) and older (OLD) men and women (age 68.4 +/- 3.3 y, BMI 27.4 +/- 3.4 kg/m(2)). The thermic effect of feeding (TEF) during weight maintenance, and changes in resting energy expenditure (REE) and respiratory quotient were determined in response to undereating by an average 3.75 MJ/d for 6 wk. In addition, body composition was measured. No significant differences among the groups were observed in TEF, fasting and postprandial respiratory quotient, or the change in fasting respiratory quotient with underfeeding. However, REE adjusted for fat-free mass and fat mass was significantly lower in OLD subjects compared with YNW and YOW subjects (P < 0.05). In addition, the REE response to weight change was significantly attenuated in the OLD subjects (P = 0.023). These data suggest that the responsiveness of energy expenditure to negative energy balance is attenuated in old age, and provide further support for the hypothesis that mechanisms of energy regulation are broadly disregulated in old age.

The influence of dietary fiber on energy regulation remains controversial. This review summarizes published studies on the effects of dietary fiber on hunger, satiety, energy intake, and body composition in healthy individuals. Under conditions of fixed energy intake, the majority of studies indicate that an increase in either soluble or insoluble fiber intake increases postmeal satiety and decreases subsequent hunger. When energy intake is ad libitum, mean values for published studies indicate that consumption of an additional 14 g/day fiber for >2 days is associated with a 10% decrease in energy intake and body weight loss of 1.9 kg over 3.8 months. Furthermore, obese individuals may exhibit a greater suppression of energy intake and body weight loss (mean energy intake in all studies was reduced to 82% by higher fiber intake in overweight/obese people versus 94% in lean people; body weight loss was 2.4 kg versus 0.8 kg). These amounts are very similar to the mean changes in energy intake and body weight changes observed when dietary fat content is lowered from 38% to 24% of energy intake in controlled studies of nonobese and obese subjects. The observed changes in energy intake and body weight occur both when the fiber is from naturally high-fiber foods and when it is from a fiber supplement. In view of the fact that mean dietary fiber intake in the United States is currently only 15 g/day (i.e., approximately half the American Heart Association recommendation of 25-30 g/day), efforts to increase dietary fiber in individuals consuming <25 g/day may help to decrease the currently high national prevalence of obesity.

We investigated the effects of food palatability on the thermic effect of feeding (TEF), substrate oxidation and circulating glucose and insulin. Healthy young men (23.4+/-1.0, SD, years, n=10) and older men (69.4+/-1.3, years, n=9) were resident in a metabolic unit for two 2-day study periods. On the second day of each period, they consumed in random order either a palatable test meal containing 2.93 MJ or a nonpalatable control meal containing the same foods in identical amounts but blended and freeze-dried into biscuit form. TEF and respiratory quotient (RQ) were measured over 6 h and blood samples were taken for measurement of glucose and insulin. Age group had no effect on TEF, RQ or circulating glucose other than to delay the time of peak TEF (P<0.002 for both meals). There was no significant effect of meal type on TEF, but RQ and circulating glucose were higher following consumption of the palatable meal (P<0.001 for both parameters). These results suggest that over 6 h postprandial, consumption of palatable foods does not increase TEF, but is instead associated with increased glycemic response and increased carbohydrate oxidation. These changes, combined with previous work on the glycemic index, predict an accelerated return of hunger and increased energy intake at subsequent meals following consumption of palatable vs. control foods. Further studies are needed to examine the possible mechanism for this previously suggested "second meal" effect of diet palatability on energy intake.

Background: Stunting increases the risk of obesity in developing countries, particularly in girls and women, but the underlying reason is not known., Objective: Our objective was to test the hypothesis that stunted children have lower energy expenditure than do nonstunted children, a factor that has predicted an increased risk of obesity in other high-risk populations., Design: A cross-sectional study was conducted in shantytown children from São Paulo, Brazil. Twenty-eight stunted children aged 8-11 y were compared with 30 nonstunted children with similar weight-for-height. Free-living total energy expenditure (TEE) was measured over 7 d by using the doubly labeled water method. In addition, resting energy expenditure (REE) was measured by indirect calorimetry and body composition was measured by dual-energy X-ray absorptiometry., Results: There were no significant associations between stunting and any measured energy expenditure parameter, including REE adjusted for weight (f1.gif" BORDER="0"> +/- SEM: 4575 +/- 95 compared with 4742 +/- 91 kJ/d, in stunted and nonstunted children, respectively) and TEE adjusted for weight (8424 +/- 239 compared with 8009 +/- 221 kJ/d, in stunted and nonstunted children, respectively). In multiple regression models that included fat-free mass and fat mass, girls had significantly lower TEE than did boys (P: < 0.05) but not significantly lower REE (P: = 0.17)., Conclusions: There was no association between stunting and energy expenditure after differences between groups in body size and composition were accounted for. However, the girls had lower TEE than did boys, which may help to explain the particularly high risk of obesity in stunted adolescent girls and women in urban areas of developing countries.

Old age is a time of vulnerability to unintentional weight loss, a factor that is associated with increased morbidity and premature death. Many possible causes of weight loss in old age have been suggested. The so-called anorexia of aging may play a particular role, by either reducing food intake directly or reducing food intake in response to such adverse factors as age-associated reductions in taste and smell, poor dentition, use of multiple prescription medicines, and depression. Recent studies also raise the question of whether a reduction in dietary variety may be important. These findings emphasize the need for regular monitoring of body weight to detect unintentional weight loss in older individuals and suggest testable ways to minimize the impact of the anorexia of aging on body weight through improved dietary management.

Inadequate energy intake is common in older individuals and is probably the major cause of unexplained weight loss. This summary highlights recent studies on possible causes of negative energy balance in older individuals suggesting that aging is associated with a significant impairment in the regulation of food intake that inhibits appropriate short-term and long-term compensation for normal fluctuations in energy intake. The combination of a reduced ability to regulate energy intake, decreased dietary variety, and disadvantageous social factors such as functional limitations, social isolation and depression, increases the risk of negative energy balance leading to weight loss in older individuals.

Background: Recent studies have questioned the accuracy of using the current recommended dietary allowances (RDAs) to predict usual energy requirements in adults., Objective: We developed equations to predict adult energy requirements from simple anthropometric and laboratory measures by using the doubly labeled water method to determine each subject's total energy expenditure (TEE), which is equal to usual energy requirements in weight-stable individuals., Design: This was a cross-sectional study conducted with 93 healthy, free-living adults [44 men and 49 women; body mass index range (in kg/m2): 18.4-31.8] aged 18-81 y. Body fat and fat-free mass were measured by underwater weighing, physical activity was estimated by using activity monitors, and resting energy expenditure was determined by indirect calorimetry. Information on anthropometric variables and reported strenuous activity was also collected., Results: Three regression equations were developed and verified for accuracy by using bootstrap analysis and doubly labeled water data published by other research groups. The first equation used information on only age, weight, height, and sex and had an SEE for prediction of TEE of 1.80 MJ/d. The second and third equations used different combinations of basic and laboratory data and had SEEs of 1.55 and 1.65 MJ/d, respectively. With use of the same analytic approaches, the RDAs for energy were shown to significantly underestimate usual energy needs by approximately 10%; the extent of underestimation was significantly greater for subjects with high TEEs than for subjects with low TEEs., Conclusion: Regression equations based on doubly labeled water measurements of TEE appear to be more accurate than the current RDAs for predicting energy requirements in healthy, nonobese adults living in affluent countries.

There remains controversy over the effect of age on postprandial thermogenesis, with some studies observing decreased postprandial thermogenesis in older subjects and other studies finding no effect of age. We investigated this issue in 8 young (25.2+/-1.8 years) and 8 older (72.2+/-2.1 years) healthy glucose-tolerant women with normal thyroid hormone status. Repeated measures of the thermic effect of feeding (TEF) were obtained following consumption of test meals containing 0, 1046, 2092, and 4184 kilojoules (kJ) by using indirect calorimetry. TEF at each meal size was determined once in the older subjects and twice in the younger subjects (during follicular and luteal phases of the menstrual cycle) for a total of 96 measurements. There was a positive dose-response between meal size and TEF (p < .001) that was not significantly affected by age group. The best single predictor of TEF expressed as a percentage of meal energy content was waist-to-hip ratio (R2=67.416, p < .02). These results indicate that aging is not associated with decreased TEF in the absence of factors such as a hypothyroid state or glucose intolerance.

The effects of aging on energy requirements and energy balance have been studied by several research groups using the doubly labeled water method. The weight of evidence from these investigations suggests that current recommended dietary allowances underestimate the usual energy needs of adults of all ages, including older adults. In addition, doubly labeled water studies have found a significant negative association between body fatness and energy expenditure for physical activity, and a significant positive association between energy expenditure for physical activity and fat-free mass. Further studies are needed to refine estimates of energy requirements for different population groups and to address the role of physical activity in the prevention and treatment of obesity.

Information on the macronutrient composition of the diet is needed in doubly labeled water studies to convert measured rates of carbon dioxide production into values for total energy expenditure. There is no general consensus, however, about the best method to determine food intake for this purpose. Four common methods of measuring food intake (7-day weighed food intake, 24-hour recall, and Fred Hutchinson Cancer Research Center/Block and Willett food frequency questionnaires) were tested for their ability to provide comparable food quotient and total energy expenditure data in doubly labeled water studies in 10 young and 10 older women. All methods gave mean values for total energy expenditure that were within 1% of each other. Individual values obtained using the 24-hour recall and food frequency questionnaires were within +/- 3% (standard deviation) of values determined using data from the 7-day weighed food record. These results suggest that it is not necessary to use time-consuming and expensive 7-day food records in doubly labeled water studies; instead, food intake data obtained more easily by 24-hour recall or food frequency questionnaire can provide comparable data.

Previous studies by our group and others have suggested that nutritional stunting may increase the risk of obesity. To investigate mechanisms that could explain a link between stunting and obesity, a 22-mo follow-up study was conducted in two groups of shantytowns school girls (7-11 y old) in São Paulo, Brazil. One group (n = 15) had mild stunting (defined using a cutoff of -1.4 Z-scores of height-for-age) but normal weight-for-height; the control group (n = 15) had normal weight and height. Similar energy intake, dietary macronutrient composition and energy expenditure were observed in the two groups. Both groups showed comparable levels of IGF-1 that were below the normal range. A significant and positive association between baseline IGF-1 and the change in height-for-age during follow-up was found in all subjects combined (P = 0.044). A significant association was found between the baseline percentage of dietary energy supplied by fat and the gain in weight-for-height during follow-up in girls with mild stunting (P = 0.048), but not in the nonstunted control girls (P = 0.245); however, the slopes of these relationships were not significantly different. This study raises the question of whether a diet high in fat may increase the susceptibility to excess body fat gain in children who are mildly stunted. Further studies are need to explore this issue and to examine the possible etiological role of low levels of IGF-1.

We examined whether older individuals have an impairment in their ability to oxidize dietary fat, a factor that could help to explain age-associated weight gain. The subjects were 16 healthy younger and older women. Fat oxidation was determined by indirect calorimetry before and after consumption of four different test meals consumed > or = 5 d apart. The intervention meals contained 0, 1046, 2092, or 4184 kJ (simulating extended fasting, and consumption of a snack, a small meal, and a moderately large meal, respectively), with 35% of energy from fat. The duration of each measurement was the amount of time required for postprandial energy expenditure to return to the premeal fasting value. A total of 96 measurements were obtained, including duplicates for all meal sizes in the younger women (in the follicular and luteal phases of the menstrual cycle). Total postprandial fat oxidation increased in proportion to meal size in the younger subjects, but did not increase above that for the 2092-kJ meal in the older women. In addition, older subjects had significantly lower total fat oxidation after consumption of the 4184-kJ meal (781 compared with 1029 kJ/measurement, P < 0.02) and also significantly greater fat deposition (745 compared with 464 kJ/measurement, P < 0.02). These findings suggest that, relative to younger women, older women have a reduced ability to oxidize dietary fat when they consume large meals.

Recent studies suggest that leptin may be an important metabolic signal for energy regulation in rodents, but the role of leptin in human energy regulation remains uncertain. Because adaptive variations in energy expenditure play an important role in human energy regulation, we investigated the relationship between leptin and energy expenditure parameters in 61 weight-stable men and women aged 18 years to 81 years who were not obese. Measurements were made of circulating leptin in the fasting state, body fat and fat free mass, resting metabolic rate (n = 61), free-living total energy expenditure (n = 52), and the thermic effect of feeding (n = 33). After statistically accounting for age, body fat, and fat free mass, there was no association between leptin and any measured energy expenditure parameter. In addition, there was no effect of age on the relationship between circulating leptin and body fat mass. These results indicate that physiological variations in circulating leptin are not linked with adaptive variations in energy expenditure in humans, in contrast to indications of this phenomenon in the ob/ob mouse.

Soluble dietary fiber is a potentially important factor determining our ability to maintain a stable energy balance and avoid obesity. However, clinical metabolic investigations have given conflicting results on the effects of soluble fiber on energy regulation, perhaps for the reasons that a) other dietary components that affect energy regulation have not always be controlled adequately and b) in the past it has been hard to ensure that subjects are consistently compliant with the dietary requirements of soluble fiber protocols. The recent development of techniques for assessing dietary compliance in metabolic studies, combined with increased control of non-fiber dietary variables that influence energy intake, should help ensure more consistent findings in future investigations.

The roles of energy expenditure and substrate oxidation in energy regulation, and the effects of factors such as aging on these parameters, remain uncertain. A re-analysis of data from two studies involving overfeeding or underfeeding in young men (22.7 +/- 0.6 [SEM] years) and older men (68.0 +/- 1.50 years) was conducted to further evaluate the adaptive capacity of energy expenditure and respiratory quotient to an increase or a decrease in energy intake. Changes in total energy expenditure (TEE) and resting energy expenditure (REE) and respiratory quotient (RQ) in response to energy imbalance were compared between subjects undergoing overfeeding by 4.1 MJ/day for 21 days, or underfeeding by 3.2 MJ/day for 21 days. Comparing responses to overfeeding or underfeeding, there was a significant TEE response to energy imbalance averaging 1.39 MJ/day and equivalent to 19% of the alteration in energy intake (p < 0.05). There was also a significant REE response to energy imbalance averaging 0.45 MJ/day (p < 0.001), and a significant RQ response in both fasting and fed states (p < 0.01). There was no significant difference between young and older men in their TEE, energy deposition or RQ responses to energy imbalance, but older men did have significantly diminished REE response to energy imbalance (p < 0.05) and a significantly delayed thermic response to a standard meal (p < 0.05). These data indicate that energy expenditure plays a significant role in attenuating the effects of alterations in energy intake on body energy stores and that, based on some measures of energy expenditure, aging is associated with a reduction in the adaptive capacity of energy expenditure to participate in energy regulation.

There is little information on the effects of the menstrual cycle on the thermic effect of feeding (TEF) and postprandial substrate oxidation. To address these issues, a dose-response study was conducted in eight young women to whom test meals containing 0, 1046, 2092 and 4148 kJ were administered on nonconsecutive days, once each during the follicular phase and once during the luteal phase of the menstrual cycle. Postprandial energy expenditure was measured until it returned to base line (test duration for the 0 kJ meal was matched to duration of 4184 kJ meal). There was no significant difference between menstrual cycle phases in the duration of the thermogenic response to any size meal. TEF, calculated by four different methods, did not differ between follicular and luteal phases, and a comparable dose-response was observed in both phases. Similarly, there was no effect of menstrual cycle phase on postabsorptive or postprandial protein, fat, or carbohydrate oxidation. In conclusion, postabsorptive and postprandial energy expenditure and substrate oxidations did not differ in young women during the follicular and luteal phases of the menstrual cycle.

The accuracy and precision of four different food intake assessment methods were evaluated in young and older women by comparing reported energy intakes with doubly labeled water measurements total energy expenditure (TEE). A study lasting 8 d was conducted in 10 young women aged 25.2+/-1.1 y (-x+/-SEM) and in 10 older women aged 74.0+/-1.4 y. Free-living TEE was measured over 7 d and food consumption was determined from weighed food intake data (7 d), a 24-h food recall (in duplicate), and two different food-frequency questionnaires [Fred Hutchinson Cancer Research Center (FHCRC)/Block and Willett, both in duplicate]. In addition, body composition was determined by using hydrodensitometry, and strenuous physical activity and the extent of dietary restraint were determined by questionnaire. In young women, 24-h recall gave mean energy intakes that were closest to measures of TEE (-0.34+/-3.71 MJ/d compared with TEE, P=0.178), and energy intakes by food-frequency questionnaires were the only intake data that correlated significantly with individual values for TEE (P<0.05). In older women, food-frequency questionnaires gave mean energy intakes that were closest to measured TEE (+0.53+/-2.95 MJ/d with the Willett questionnaire and -1.19+/-3.02 MJ/d with FHCRC/Block questionnaire). No energy intake data from this group correlated significantly with values for TEE. The 7-d weighed dietary intakes were significantly lower than measured TEE in both young and older women (-2.0 MJ/d in young and older women combined, P<0.001), and did not correlate significantly with values for TEE, although they did most closely mirror the mean difference in TEE between the young and older women (2.30 MJ/d for TEE and 2.11 MJ/d for 7-d weighed intake). These data suggest that none of the methods studied gave accurate estimates of the usual energy requirements of individual subjects. In addition, the results suggest that for some types of studies, simple methods for assessing group mean dietary intake may actually give more accurate information than weighed dietary intakes.

Relatively little is known about the influence of age on energy regulation during energy imbalance. We compared the effects of underfeeding on changes in energy expenditure, substrate oxidation, and body energy loss between young men (age 22.0 +/- 0.9 [SEM] years) and older men (age 66.0 +/- 1.8) who were leading unrestricted lives. Changes in total energy expenditure (TEE), resting energy expenditure (REE), the thermic effect of feeding (TEF), respiratory quotient, and body energy loss were determined in response to undereating by 3.17 +/- 0.16 Megajoule (MJ)/day for 21 days in 19 healthy subjects consuming a typical diet. No significant effects of age were observed in changes in TEE, REE, TEF, or body energy loss in response to underfeeding. Thus, older men do not appear to have any impairment of energy conservation during negative energy balance compared to young men. This normal pattern of energy conservation during undereating together with the previously demonstrated reduction in energy dissipation during overeating can be predicted to promote body fat deposition in older men during the cycles of positive and negative energy balance that occur during normal life. This finding may help to explain the increased body fat mass in older individuals.

Relatively little is known about the influence of age on energy regulation during energy imbalance. We compared the effects of overfeeding on changes in energy expenditure, substrate oxidation, and energy deposition between young men (age 23.7 +/- 1.1 [SEM] years) and older men (age 70.0 +/- 7.0) of normal body weight who were leading unrestricted lives. Changes in total energy expenditure, resting energy expenditure (REE), the thermic effect of feeding (TEF), respiratory quotient (RQ), and body energy content were determined in response to overeating by 4.09 +/- 0.07 Megajoule (MJ)/day for 21 days in 16 healthy subjects consuming a typical diet. After excluding data from one young subject with unusual results and adjusting for individual differences in excess energy intake, there was a tendency towards a smaller increase in REE in older men compared to the young men (p = .07) which was accounted for by their lower fat-free mass (p = .016). There was also a significantly smaller increase in resting energy expenditure averaged over fasting and fed states (i.e, REE + TEF) with overfeeding in older men than in young men (p < .01). Combined, these smaller increases in energy expenditure with overfeeding in the older subjects averaged an estimated 365 kilojoule (kJ)/day (8.9% of the excess energy intake) (p < .02). There were also significant effects of age on fasting RQ (p < .001) and the change in RQ with overfeeding (p < .001), but no significant increase in energy expenditure for physical activity and thermoregulation with overfeeding in either age-group. These results are consistent with the suggestion that older individuals experience both a reduction in the ability to increase energy expenditure, and an alteration in the pattern of substrate utilization, in response to overfeeding. These changes may promote cumulative increases in body energy during normal cycles of positive energy balance unless compensated for by adaptive variations in energy intake.

The effects of aging on energy requirements and energy expenditure were investigated in 35 healthy young men (mean +/- SE age, 22.7 +/- 0.6 y) and elderly men (68.0 +/- 1.5 y). Over a 10-d metabolic balance study, measurements were made of metabolizable energy intake for weight maintenance, total energy expenditure, resting energy expenditure, and thermic effect of feeding. Values for both metabolizable energy intake and total energy expenditure were significantly higher than the current recommended dietary allowance for energy in both age groups (P < 0.01). Total energy expenditures were 14.48 +/- 0.65 and 11.26 +/- 5.40 MJ/d in young and elderly men, respectively. The difference in total energy expenditure between the groups was accounted for by a significant decrease in all the major components of expenditure. These results suggest that the current recommended dietary allowances for energy may underestimate the usual energy needs of healthy adult men.

The role of energy expenditure in the development of obesity remains unclear. This issue is examined using data from prospective studies of energy expenditure and obesity, the effects of overfeeding and diet composition on energy expenditure, and studies of the relationship between energy expenditure for physical activity and body composition. The combined results from these investigations strongly support the view that low energy expenditure can facilitate rapid weight gain in susceptible individuals. It is speculated that, in susceptible individuals, low energy expenditure for resting energy expenditure as well as physical activity are part of a range of mechanisms available for providing surplus energy for rapid weight gain. In addition, both cross-sectional and intervention studies indicate that there is an equilibration between the level of energy expenditure for physical activity and body fat content. While genetic and other factors clearly play an important role in this relationship, it appears that a modest reduction in body fat content can be achieved by increasing energy expenditure for physical activity in physical exercise programs.

There is little information on the effects of age on energy requirements in women. This issue was investigated in a cross-sectional study of 10 normal-weight young women aged 25.2 +/- 1.1 y (mean +/- SEM) and 10 normal-weight older women aged 74.0 +/- 1.4 y. In a 9-d study, measurements were made of free-living total energy expenditure (TEE) by using the doubly labeled water technique, body composition by using hydrodensitometry, and resting energy expenditure (REE) by using indirect calorimetry. Mean values for reported levels of strenuous activity were within the expected range in both groups (31 +/- 13 min/d in the young group and 7 +/- 2 min/d in the older group). Energy requirements expressed as the ratio of TEE to REE were 1.80 +/- 0.10 and 1.62 +/- 0.06 (P < 0.01) in the young and older group, respectively. When values for REE predicted from body weight (pREE) were used, as suggested in the current recommended dietary allowances (RDAs), the ratios of TEE to pREE in the two groups were 1.85 +/- 0.10 and 1.54 +/- 0.04 (P < 0.05). The RDAs significantly under-predicted the energy requirements of the young group (P < 0.05), but there was no significant underprediction in the older group. Although obtained in a relatively small number of subjects, these results provide no evidence to indicate that the current RDAs underestimate the energy requirements of older women, in contrast with previous observations of an underestimation of energy requirements by the RDAs in older men.

The role of energy expenditure in energy regulation remains a subject of continuing controversy. New data have emerged from studies conducted over the last decade demonstrating that energy expenditure is a critical factor contributing to successful energy regulation in normal individuals, as well as to the disregulation of energy balance that characterizes obesity. Reduced energy expenditure appears to facilitate weight gain in individuals susceptible to obesity and also appears to reduce the extent of body energy loss during undereating in both lean and obese individuals. The magnitude of the reduction in energy expenditure during, and perhaps after, weight loss is greater than expected on the basis of the reduction in body weight and appears to occur in response to undefined underlying determinants of energy regulation. In addition, exercise intervention studies and cross-sectional investigations of the relationship between energy expenditure for physical activity and body composition demonstrate an apparent equilibration between physical activity and body fat content. This equilibration is suggestive of a direct influence of physical activity on the underlying metabolic determinants of energy balance.

A double-blind study was conducted to determine between-laboratory variability in the doubly labeled water method for measurement of total energy expenditure in humans, and to compare the accuracy and precision of three widely-used procedures for calculating rates of carbon dioxide production from the original isotope data. Eighteen laboratories from five countries participated in the study. All laboratories were provided with five water standards containing varying amounts of 2H and 18O, and in addition 11 laboratories were provided with urine and dose specimens from one (six laboratories) or two (five laboratories) healthy elderly subjects of normal height and weight undergoing a calorimetric validation of the doubly labeled water method. The data from the five water standards were analyzed to predict between-laboratory variability in the doubly labeled water technique in all laboratories. In addition, data from the subjects were analyzed using the "slope-intercept", "2-point" and "modified" methods of calculation. The results confirm that the doubly labeled water method can be an accurate technique for the measurement of energy expenditure in adult human subjects in some laboratories. However, there was substantial between-laboratory variability in the results and some laboratories returned physiologically impossible results. There was no significant effect of calculation procedure on the accuracy of the technique in this limited comparison, although the slope-intercept procedure appeared to be more susceptible to analytical error than the other procedures. The isotope standards analyzed by participants in this study will be made available to other investigators on request.

Objective: To investigate the effects of aging on mechanisms of body energy regulation and thereby determine the causes of unexplained weight loss in older persons, a factor predisposing to premature death and disability., Design: Dietary intervention study., Setting: Metabolic ward and outpatient., Participants: The subjects were 35 healthy younger and older men of normal body weight consuming a diet of typical composition and performing usual activities., Main Outcome Measures: Subjects were either overfed by a mean (+/- SD) of 4.09 (+/- 0.26) MJ/d (n = 17) or underfed by 3.17 (+/- 0.68) MJ/d (n = 18) for 21 days. Measurements were made of changes in body weight, body composition, and energy expenditure during overfeeding or underfeeding, and of subsequent voluntary nutrient intakes and changes in body weight., Results: There was no significant effect of aging on changes in body composition, body weight, or energy expenditure with overfeeding or underfeeding. However, following overfeeding, younger men exhibited spontaneous hypophagia, whereas the older men did not (mean [+/- SD] changes in energy intake relative to control values were -2.11 [+/- 2.18] and 1.55 [+/- 2.11] MJ/d, respectively; P = .006). As a result, the younger men lost the excess body weight gained during overfeeding but the older men did not. Similarly, following underfeeding, the younger men exhibited hyperphagia while the older men did not (mean [+/- SD] changes in energy intake relative to control values were 1.88 [+/- 2.31] and -0.52 [+/- 1.54] MJ/d, respectively; P = .02), and as a result the older men failed to regain the weight lost during underfeeding., Conclusions: These results in 35 men suggest that aging may be associated with a significant impairment in the ability to control food intake following overeating or undereating. Since overeating and undereating occur routinely as part of the normal pattern of energy regulation, the findings reported herein may help to explain the vulnerability of older persons to unexplained weight gain and weight loss.

We investigated the importance of adaptive variations in energy expenditure in the regulation of energy balance in young and elderly men of normal body weight leading unrestricted lives. Changes were measured in total and resting energy expenditure and body composition in response to overeating by approximately 4.2 MJ/d or undereating by 3.3 MJ/d for 21 d in 39 young and elderly men consuming a typical diet. In the young men, an average of 85-90% of the excess energy intake during overeating was deposited. During underfeeding, mobilization of body energy compensated for an average of 65% of the energy deficit in these subjects. The resting metabolic rate, averaged for fasting and fed states, increased during overfeeding (+0.63 +/- 0.20 MJ/d, P < 0.01) and decreased during underfeeding (-0.42 +/- 0.12 MJ/d), but at least some of these changes were due to the obligatory expenditure associated with nutrient assimilation. There was no significant change in energy expenditure for physical activity or thermoregulation from overfeeding or underfeeding. Preliminary results indicate that aging had no effect on responses to overfeeding or underfeeding. These findings suggest that adaptive variations in energy expenditure are not the major determinant of energy regulation in young adults of normal body weight and that, instead, energy balance is maintained on a day-to-day basis through the control of nutrient intakes.

The energy requirements of healthy elderly men were investigated by measuring total energy expenditure (TEE), body composition and resting energy expenditure (REE), using 2H2(18)O techniques and indirect calorimetry during ten days when a weight maintaining diet was consumed. Values for TEE/REE (1.75 +/- 0.05, s.e.) were significantly higher than the recommended dietary allowances (RDAs) for energy in this age group, as were previously reported values for TEE/REE in a group of young men in the same experimental protocol. There was a significant negative association between TEE/REE (a physical activity indicator) and body fat mass. Combining data from the elderly men in this study and the young men studied previously, age and TEE/REE together accounted for 73% of the variation in body fat mass between individuals. These results lend additional weight to the suggestion that the current RDAs for energy may significantly under-estimate usual energy requirements. They also indicate that the low levels of energy expenditure suggested by the RDAs may favour unnecessarily high levels of body fat mass and that increased levels of energy expenditure are desirable.

The double labeled water technique for determination of the rate of total energy expenditure in human subjects is based on measurement of the differential rates of disappearance of 2H and 18O from body water following oral administration of 2H218O. Two calculation procedures, the "two-point" and "slope-intercept" methods of calculation have previously been validated for use in humans. We describe here a computer program. DLW, that provides options to calculate doubly labeled water data in each of these accepted ways.

We investigated the mechanisms of body weight regulation in young men of normal body weight leading unrestricted lives. Changes in total and resting energy expenditure, body composition, and subsequent voluntary nutrient intakes in response to overeating by 4,230 +/- 115 (SE) kJ/day (1,011 +/- 27 kcal/day) for 21 days were measured in seven subjects consuming a typical diet. On average, 85-90% of the excess energy intake was deposited (with 87% of this amount in fat and 13% in protein on average). There was no detectable difference between individuals in susceptibility to energy deposition. The resting metabolic rate, averaged for fasting and fed states, increased during overfeeding (mean +/- SE, 628 +/- 197 kJ/day, P less than 0.01), but at least some of this amount was obligatory expenditure associated with nutrient assimilation. No significant increase in energy expenditure for physical activity or thermoregulation resulted from overfeeding. Thus energy expenditure did not substantially adapt to increased energy intake. However, significant decreases in voluntary energy intake (1,991 +/- 824 kJ/day, P less than 0.05) and fat intake (48 +/- 11 g/day, P less than 0.01) followed overeating, indicating that adaptive changes in nutrient intakes can contribute significantly to body weight regulation after overeating.

Energy intake in breast fed infants is uncertain. The doubly labelled water method was used to measure, simultaneously and non-invasively, energy expenditure, energy intake, milk volume intake, energy deposition, and the energy content of breast milk in 12 "free living" breast fed babies at 5 and 11 weeks of age. The validity of this new approach was assessed in a parallel study in 12 formula fed infants. The babies who were exclusively breast fed expended 1.28 and 1.68 MJ/day at five and 11 weeks and had intakes of 1.81 and 2.22 MJ/day; these intakes were associated with normal growth but were well below those recommended previously. At five and 11 weeks the calculated energy content of breast milk was 0.24 and 0.25 MJ/100 ml, which is substantially lower than that commonly reported in milk obtained unphysiologically by expression of the breast. These data cast doubt on the widely used published standards for infant feeding.

The possibility that lactation increases the efficiency of energy use was investigated by comparing energy expenditure on activity and maintenance in virgin and lactating rats fed either ad libitum or restricted amounts of food. Energy expenditure was determined, by difference, in a nutrient balance study. Lactating rats fed ad libitum expended 34.9% less energy on activity and maintenance than did control animals. Of this change, 82% was specifically associated with lactation, but the remaining 18% was associated with the negative energy balance that occurred during lactation. Lactating rats fed restricted amounts of food expended less energy on activity and maintenance than did virgin rats fed at the same level of restriction, but this change was associated with increased negative energy balance and not specifically with lactation. These results indicate that the efficiency of energy use is increased substantially during lactation in the rat, regardless of the level of energy intake, and that mechanisms associated with negative energy balance play an important role in the change.

We investigated the contributions of low energy expenditure and high energy intake to excessive weight gain in infants born to overweight mothers. The subjects were infants of 6 lean and 12 overweight mothers, recruited soon after birth. Total energy expenditure and metabolizable energy intake were measured with a new doubly labeled water method over a period of seven days when the infants were 3 months of age, and the postprandial metabolic rate was measured by indirect calorimetry when the infants were 0.1 and 3 months of age. The results were related to weight gain in the first year of life. No significant difference was observed between infants who became overweight by the age of one year (50 percent of infants born to overweight mothers) and those who did not, with respect to weight, length, skinfold thicknesses, metabolic rate at 0.1 and 3 months of age, and metabolizable energy intake at 3 months. However, total energy expenditure at three months of age was 20.7 percent lower in the infants who became overweight than in the other infants (means +/- SE, 256 +/- 27 and 323 +/- 12 kJ per kilogram of body weight per day; P less than 0.05). This difference could account for the mean difference in weight gain. These data suggest that reduced energy expenditure, particularly on physical activity, was an important factor in the rapid weight gain during the first year of life in infants born to overweight mothers.

A new method is described for measuring the rate of carbon dioxide production, and hence for estimating energy expenditure, in preterm infants receiving assisted ventilation. In a validation study, the mean error in carbon dioxide measurement was 1.9%. Measurements were made, over a 45-min period, on 11 sick, ventilated subjects and carbon dioxide production rate was 5.2 +/- 0.7 (SD) ml/min X kg body weight. We suggest that continuous monitoring of carbon dioxide output will contribute to the clinical assessment of the effects of different ventilator settings on pulmonary gas exchange and that estimated values for energy expenditure will be of value in nutritional studies on sick ventilated infants.

The energy costs of depositing fat and protein in the low-birth-weight infant were determined by multiple-regression analysis from published information on metabolizable-energy intake and fat and protein deposition in groups of subjects fed different dietary regimes. The total energy requirement for deposition was 1.17 kJ/kJ deposited for fat (ie, 1 kJ deposited and 0.17 kJ expended for deposition, and 2.38 kJ/kJ for protein. These values are similar to published determinations for animal species with simple stomachs. The metabolizable-energy requirement for weight gain during infancy was calculated (range, 12.2-25.1 kJ/g, or 2.9-6.0 kcal/g; means, 18.7 kJ/g, or 4.5 kcal/g) from the energy costs of fat and protein deposition and published information on changes in body composition during the first year of life.

The doubly labeled water method was compared with indirect calorimetry and a nutrient-balance study for simultaneous determination of rates of CO2 production, energy expenditure, and water intake over 5 days in four preterm infants. Additionally, metabolizable energy (ME) intake estimated using the isotope procedure (as energy expenditure plus an estimate for energy deposition based on weight gain), was compared to ME intake measured in the balance study. Compared to values obtained by traditional methods, calculated CO2 production, energy expenditure, and water intake differed by -1.4 +/- 4.8% (SD), +0.3 +/- 2.6%, and +5.7 +/- 1.4%, respectively; the difference in water intake was significant (p less than 0.05). Calculated ME intakes were 5.3 +/- 19.3% less than measured intakes, but the difference was not significant. These findings indicate that the doubly labeled water method can provide accurate information on rates of CO2 production, energy expenditure, and water intake in preterm infants, but individual estimates of ME intake may be subject to substantial error.

The basis of the doubly labeled water method is measurement of the differential rates of disappearance of two isotopes of water (H2 18O and either 2H2O or 3H2O, administered at the start of the study) from body water. Published studies indicate that, in its current forms, this technique can be used to provide accurate and reasonably precise information on carbon dioxide production, total body water, and water intake in free-living humans and many small animals. Total energy expenditure can be calculated from carbon dioxide production with little loss of precision. Metabolizable energy intake can also be predicted, as the sum of total energy expenditure plus an estimate for the change in body energy stores during the measurement, but this prediction is unlikely to be accurate and precise unless the subject is in approximate energy balance.

The role of diet-induced thermogenesis (DIT) in the regulation of energy utilization in preterm infants was investigated by measuring energy expenditure and nutrient deposition in groups of subjects fed either banked drip breast milk (BBM) or a preterm formula (PF). Nutrient deposition was determined by combining a 3-d nutrient balance study and measurement of energy expenditure. Infants fed PF consumed 57 per cent more metabolizable energy (ME) than those fed BBM. There were significant differences between groups in energy expenditure, energy deposition and protein deposition; 76 per cent of the additional ME intake consumed by the PF-fed group was deposited while the remaining 24 per cent was expended. Infants fed PF gained weight 39 per cent faster than those fed BBM (19, compared to 14 g/kg/d), and deposited 128 per cent more fat and 86 per cent more protein. These findings indicate that nutrient deposition, rather than DIT, was the primary use of the extra ME received by the infants fed PF. However, the effect of the high energy intake on weight gain in these subjects was reduced, compared to its effect on nutrient deposition, by increases in the concentrations of fat and protein in new tissue.

Variations in background 2H and 18O abundances in body water influence the accuracy and precision of the 2H218O method for determination of energy expenditure. To investigate the effect of weaning during infancy on background 2H and 18O abundances, urine samples from 44 breast- or formula-fed infants aged 5-16 wk were analyzed. 2H and 18O abundances were significantly higher (P less than 0.001) in breast- than in formula-fed infants. The relationship between 2H and 18O abundances was linear and independent of diet [slope, 4.16 +/- 0.43 (SE)]. By use of this information, the effect of weaning on the accuracy of the 2H218O method was evaluated, taking into account the effect of 2H-18O abundances in the isotope loading dose. In infants weaned completely from breast milk to formula during the measurement, energy expenditure can be overestimated by 18.0%, even if 2H-18O abundances in the isotope dose equal the ratio of naturally occurring background changes. However, this error can be reduced to less than 3.0% by manipulating the study duration and isotope dose. During gradual weaning, the overestimation of energy expenditure is only 0.3-2.0%.

The effect of ambient temperature on the energy requirements of the lactating rat was investigated. Ambient temperature was maintained at 13, 20 or 25 degrees C during lactation, and digestible energy (DE) intake, milk output and energy balance were measured between 4 and 12 d post partum. Ambient temperature did not significantly affect DE intake. Milk output was highest in the rats housed at 13 degrees C and lowest in those kept at 25 degrees C, although the rate of body fat mobilization was lowest in the rats kept at 20 degrees C and highest in the rats kept at 25 degrees C. Energy expenditure on activity and maintenance, determined from the difference between DE intake and body nutrient mobilization plus the energy used for milk production, was significantly higher in the rats housed at 25 degrees C than in those kept at 13 degrees C. This is an opposite trend to that which occurs in nonlactating rats. The results indicate that the gross efficiency of energy utilization during lactation is higher at 13 degrees C than it is at 25 degrees C in the rat.