Energy expenditure in underweight free-living adults: impact of energy supplementation as determined by doubly labeled water and indirect calorimetry

The Physiological Regulation of Body Fat Mass

Disturbances inbody weight and adiposity in both humans and animals are met by compensatory adjustments in energy intake and energy expenditure, suggesting that body weight or fat is regulated. From a clinical viewpoint, this is likely to contribute to the difficulty that many people with obesity have in maintaining weight loss. Finding ways to modify these physiologic responses is likely to improve the long-term success of obesity treatments.

Comparison of total energy intakes estimated by 24-hour diet recall with total energy expenditure measured by the doubly labeled water method in adults

BACKGROUND/OBJECTIVES

The doubly labeled water (DLW) method is the gold standard for estimating total energy expenditure (TEE) and is also useful for verifying the validities of dietary evaluation tools. In this study, we compared the accuracy of total energy intakes (TEI) estimated by the 24-h diet recall method with TEE obtained using the doubly labeled water method.

SUBJECTS/METHODS

This study involved 71 subjects aged 20–49 yrs. Over a 14-day period, three 24-h diet recalls per subject (2 weekdays and 1 weekend day) were used to estimate energy intakes, while TEE was measured using the DLW method. The paired t-test was used to determine the significance of differences between TEI and TEE results, and the accuracy of the 24-h recall method was determined by accuracy predictions percentage, root mean square error, and bias.

RESULTS

Average study subject age was 33.4 ± 8.6 yrs. The association between TEI and TEE was positive and significant (r = 0.463, P < 0.001), and the difference between TEI (2,084.3 ± 684.2 kcal/day) and TEE (2,401.7 ± 480.3 kcal/day) was also significant (P < 0.001). In all study subjects, mean TEI was 12.0% (307.5 ± 629.3 kcal/day) less than mean TEE, and 12.2% (349.4 ± 632.5 kcal/day) less in men and 11.8% (266.7 ± 632.5 kcal/day) less in women. Rates of TEI underprediction for all study subjects, men, and women, were 60.5%, 51.4%, and 66.7%, respectively.

CONCLUSIONS

This study shows that 24-h diet recall underreports energy intakes. More research is needed to corroborate our findings and evaluate the accuracy of 24-h recall with respect to additional demographics.

The biology of human overfeeding: A systematic review

This systematic review has examined more than 300 original papers dealing with the biology of overfeeding. Studies have varied from 1 day to 6 months. Overfeeding produced weight gain in adolescents, adult men and women and in older men. In longer term studies, there was a clear and highly significant relationship between energy ingested and weight gain and fat storage with limited individual differences. There is some evidence for a contribution of a genetic component to this response variability. The response to overfeeding was affected by the baseline state of the groups being compared: those with insulin resistance versus insulin sensitivity; those prone to obesity versus those resistant to obesity; and those with metabolically abnormal obesity versus those with metabolically normal obesity. Dietary components, such as total fat, polyunsaturated fat and carbohydrate influenced the patterns of adipose tissue distribution as did the history of low or normal birth weight. Overfeeding affected the endocrine system with increased circulating concentrations of insulin and triiodothyronine frequently present. Growth hormone, in contrast, was rapidly suppressed. Changes in plasma lipids were influenced by diet, exercise and the magnitude of weight gain. Adipose tissue and skeletal muscle morphology and metabolism are substantially altered by chronic overfeeding.

Claims of anomalously long fasting: An assessment of the evidence from investigated cases

BACKGROUND

Throughout history and to the present day, there have been reports of people claiming inedia, i.e., an anomalous long-term abstinence from food or from food and fluid. Some were isolated and monitored and their abstinences confirmed. This raises the question of whether there may be an anomaly with wide implications that science has overlooked. On the other hand, there have been cases of exposed fraud. The reports on the studies are scattered and it can be difficult to judge their rigor and the strength and implications of their evidence. A critical evaluation seems useful.

OBJECTIVES

The objectives were to obtain an overview of investigated cases of claimed inedia, to assess the anomaly of the claims and study results, to assess the quality of the studies, and to identify deception methods to inform future safeguards.

METHOD

I developed criteria for differentiating normal from anomalous nutrition and fasting and for assessing the quality of inedia studies. Studies found through a systematic search were then assessed and the features of cases of fraud extracted.

RESULTS

47 eligible investigations of 38 claimants were found. Out of the 38 cases, results were assessed as (seemingly) anomalous in 11, with nine cases of monitored food and fluid deprivation ranging from 14 to 68 days (median 28 days), and two cases of food deprivation for 365 and 411 days. In 17 cases, anomaly was assessed as not confirmed due to issues with study design or reporting. Fraud was established in 10 cases. Deception methods were creative. Post-1900 studies were also assessed for quality. Quality was not considered adequate in any.

CONCLUSIONS

I consider the evidential status of inedia unconfirmed as no assessed study had both anomalous findings and impeccable quality. However, quality was often downgraded due to reporting issues and it cannot be concluded in reverse that all claimants with anomalous results were able to deceive the investigators. The results of many studies are curious and demand further research. The conducted analysis provides guidance for improving rigor and transparency in future studies.

Special Considerations for Measuring Energy Expenditure with Doubly Labeled Water under Atypical Conditions

The global increase in the prevalence of obesity has dramatically increased interest in understanding the factors that influence human total energy expenditure (TEE). This in turn has increased interest in the doubly labeled water (DLW) method, a technique for measurement of total energy expenditure in free-living humans. The increasing use of this method is attributed to its portability, objectivity, minimal invasiveness, high accuracy and good precision. Although a relatively standard protocol for the method has emerged, the new generation of users often is unfamiliar with rationale behind aspects of the protocol as well as the approaches to avoid or correct for in situations that are not covered by the standard protocol procedure. The primary uncommon situations like introduction of isotopically different diet and fluids with or without geographical relocation, seasonal and temperature variations, activity level of participants etc. during or prior to the DLW measurements can lead to shift in baseline abundance of ²H and ¹⁸O or tracer elimination, resulting in moderate to large errors in the measured TEE. These unique situations call for special modifications to the conventional protocol to minimize errors. The objective of the present review was to assemble a list of frequently asked questions and the issues they represent, and then examine the available literature to describe and explain the modifications to the standard DLW protocol to maintain the method's accuracy. This discussion of DLW protocol modification can be an excellent resource for investigators who intend to use this measurement technique for interesting and uncommon study designs.

Energy expenditure in adults living in developing compared with industrialized countries: a meta-analysis of doubly labeled water studies

BACKGROUND

There is an assumption that people in developing countries have a higher total energy expenditure (TEE) and physical activity level (PAL) than do people in developed nations, but few objective data for this assertion exist.

OBJECTIVE

We conducted a meta-analysis of TEE and PAL by using data from countries that have a low or middle human development index (HDI) compared with those with a high HDI to better understand how energy-expenditure variables are associated with development status and population differences in body size.

DESIGN

We performed a literature search for studies in which energy expenditure was measured by using doubly labeled water. Mean data on age, weight, body mass index (BMI; in kg/m(2)), TEE, and PAL were extracted, and HDI status was assessed. Pooled estimates of the mean effect by sex were obtained, and the extent to which age, weight, HDI status, and year of publication explained heterogeneity was assessed.

RESULTS

A total of 98 studies (14 studies from low- or middle-HDI countries) that represented 183 cohorts and 4972 individuals were included. Mean (±SE) BMI was lower in countries with a low or middle HDI than in those with a high HDI for both men and women (22.7 ± 1.0 compared with 26.0 ± 0.7, respectively, in men and 24.3 ± 0.7 compared with 26.6 ± 0.4, respectively, in women). In meta-regression models, there was an inverse association of age (P < 0.001) and a positive association of weight (P < 0.001) with TEE for both sexes; there was an association of age only in men with PAL (P < 0.001). There was no association of HDI status with either TEE or PAL.

CONCLUSION

TEE adjusted for weight and age or PAL did not differ significantly between developing and industrialized countries, which calls into question the role of energy expenditure in the cause of obesity at the population level.

The usefulness of an accelerometer for monitoring total energy expenditure and its clinical application for predicting body weight changes in type 2 diabetic korean women

BACKGROUND

The purpose of this study was to evaluate the usefulness of an accelerometer in predicting body weight (BW) change during a lifestyle intervention and to find out whether exercise or overall physical activity is associated with change in insulin sensitivity and body composition.

METHODS

A total of 49 overweight (body mass index [BMI] ≥ 23 kg/m(2)) women with diabetes were enrolled and performed lifestyle intervention while monitoring BW, total energy expenditure (TEE) and physical activity energy expenditure (PAEE) using an accelerometer, and energy intake (EI) using a three-day dietary record at baseline and every 2 weeks for 12 weeks. We assessed body composition using bioimpedance analysis and compared the actual BW change to the predicted BW change, which was calculated from the energy deficit (ED) between EI and TEE (ED = EI-TEE).

RESULTS

Mean age was 57.2 years, duration of diabetes was 8.0 years, and BMI was 27.8 kg/m(2). There was no significant difference between EI and TEE at baseline. For 12 weeks, the ED was 474.0 kcal·day(-1), which was significantly correlated with BW change (-3.1 kg) (r = 0.725, P < 0.001). However, the actual BW change was 50% lower than the predicted BW change. Both TEE and PAEE correlated with change in K(ITT) (r = 0.334, P = 0.019; r = 0.358, P = 0.012, respectively), BMI (r = -0.395, P = 0.005; r = -0.347, P = 0.015, respectively), and fat mass (r = -0.383, P = 0.007; r = -0.395, P = 0.005, respectively), but only TEE correlated with fat free mass change (r = -0.314, P = 0.030).

CONCLUSION

The accelerometer appears to be a useful tool for measuring TEE under free-living conditions for both short- and long-term periods.

Impact of seasonal scarcity on energy balance and body composition in peasant adolescents from Calakmul, Campeche Mexico

A time allocation and anthropometric study were performed on 46 male and 38 female adolescents from 16 peasant households from two different adaptive strategies in the municipio of Calakmul, Campeche Mexico to see if they could maintain energy balance during the annual scarcity season. These strategies were called: "household subsistence agricultural strategy" (HSA) and "household commercial agricultural strategy" (HCA). Each month, from June 2001 to May 2002, adolescents were measured and followed for 24 h. Their activities were recorded at 15 min intervals. Weight for age (W/A), height for age (H/A), body mass index (BMI), arm muscle area, arm fat area, total energy expenditure (TEE), activity energy expenditure (AEE), and basal metabolic rate (BMR) were estimated and the data compared between seasons using a repeated measurements analysis of variance. The results suggest that HCA offers their adolescents better buffering against seasonal scarcity, and that HSA males are better protected than females. HCA adolescents didn't show significant losses of weight, and HCA females lost body fat during the scarcity season. HSA vulnerability was observed in W/A and BMI z score reductions during the scarcity season. It also reflected itself in stunted adolescent males and adolescent females with fewer fat reserves. HSA adolescents reduced their BMR to down regulate their energy expenditure during the scarcity season without reducing TEE and physical activity levels. HSA females lost muscle mass during the scarcity season while HSA males didn't. This difference was associated with a more demanding work schedule throughout the year for females.

Validation study of energy expenditure and intake during calorie restriction using doubly labeled water and changes in body composition

BACKGROUND

Clinical trials involving calorie restriction (CR) require an assessment of adherence to a prescribed CR with the use of an objective measure of energy intake (EI).

OBJECTIVE

The objective was to validate the use of energy expenditure (EE) measured by doubly labeled water (DLW), in conjunction with precise measures of body composition, to calculate an individual's EI during 30% CR.

DESIGN

Ten participants underwent 30% CR for 3 wk. During the last week (7 d), 24-h EE was measured in a respiratory chamber and simultaneously by DLW (EEDLW). EI was calculated from 7-d EE measured by DLW and from changes in energy stores (ES) (weight and body composition). Calculated EI was then compared with the actual EI measured in the chamber by using the following equations: calculated EI (kcal/d) = EEDLW + DeltaES, where DeltaESFM/FFM (kcal/d) = (9.3 x DeltaFM, g/d) + (1.1 x DeltaFFM, g/d), FM is fat mass, and FFM is fat-free mass.

RESULTS

We found close agreement (R = 0.88) between EE measured in the metabolic chamber and EEDLW during CR. Using the measured respiratory quotient, we found that the mean (+/-SD) EE(DLW) was 1934 +/- 377 kcal/d and EE measured in the metabolic chamber was 1906 +/- 327 kcal/d, ie, a 1.3 +/- 8.9% overestimation. EI calculated from EEDLW and from changes in ES was 8.7 +/- 36.7% higher than the actual EI provided during the chamber stay (1596 +/- 656 kcal/d).

CONCLUSIONS

DLW methods can accurately estimate 24-h EE during CR. Although the mean difference between actual and calculated EIs for the group was small, we conclude that the interindividual variability was too large to provide an assessment of CR adherence on an individual basis.

Factors associated with the increase in resting energy expenditure during refeeding in malnourished anorexia nervosa patients

BACKGROUND

In malnourished anorexia nervosa (AN) patients, body-weight gain during refeeding is slowed by an increase in resting energy expenditure (REE).

OBJECTIVE

The objective of the study was to identify factors associated with the increase in REE during refeeding.

DESIGN

Before and 8, 30, and 45 d after the beginning of refeeding, REE was studied by indirect calorimetry in 87 female AN patients [x +/- SD age: 23.4 +/- 7.9 y; body mass index (in kg/m2) 13.2 +/- 1.3]. Energy intake, body composition (by bioelectrical impedance analysis), physical activity, smoking behavior, abdominal pain, anxiety, depressive mood, serum thyrotropin and thyroid hormone, and urinary catecholamines were measured. REE was also evaluated in 18 patients after 1 y of recovery.

RESULTS

By day 8, REE increased from 3.84 +/- 0.6 to 4.36 +/- 0.59 MJ/d (P < 0.01). This increase (13.4%) was significantly (P <0.01) greater than that expected on the basis of the increase in fat-free mass (FFM; 1.6%). Thereafter, the ratio of REE to FFM remained high and, in multivariate analysis, was significantly related to 4 factors: energy intake (P <0.01), anxiety (P <0.01), abdominal pain (P <0.05), and depressive mood (P <0.05). The ratio also increased significantly with physical activity (P <0.01) and cigarette smoking (P <0.02). This rise in REE leveled off after recovery from AN.

CONCLUSION

In AN patients, the rise in REE observed during refeeding was independently linked to anxiety level, abdominal pain, physical activity, and cigarette smoking, and it contributed to resistance to weight gain.

Food intake in the real world: implications for nutrition and aging

Nutrient intakes are affected by two classes of factors, physiological and environmental. In the real world, environmental variables such as social factors, palatability, and the time of eating appear to have large influences on amounts ingested in the short-term. Physiological control mechanisms also operate to regulate intake, and they induce compensatory responses to deviations from the norm. These physiological influences only appear to have weak influences on short-term intake unless there are large deviations from the normal state, but over the long-term they act patiently and persistently to rectify the excesses produced by environmental fluctuations and thereby tend to maintain a relative balance between energy intake and expenditure. As individuals age there is a progressive decline in physiological function including the mechanisms that act to control intake in the young. This should not produce a problem in a healthy individual in a stable environment: however, if that situation should change due to illness or an environmental change such as the death of a spouse, which produces decline in intake, elderly individuals would not have the physiological mechanisms present to compensate. Thus, the deficit in energy intake would not be replaced, and the lower level of intake would be maintained as long as the new health condition or environment remains stable. Hence, the decline in the effectiveness of the physiological systems with age makes the elderly particularly vulnerable and unable to rebound from deficits. Although the elderly have difficulty compensating for deficits automatically by physiologically-induced adjustments, the studies of real world intake reviewed in this article suggest that compensation can be produced by adjustments to the environment. The elderly appear to be as responsive to environmental factors as younger individuals. In particular, they appear to increase intake in response to social facilitation, diurnal rhythms, the eating environment, and palatability to the same extent as their juniors. These data suggest that alterations in the social, temporal, environmental, or hedonic conditions of eating could induce desired alterations in the nutrient intakes of the elderly. The study of real world eating behavior has produced evidence that suggests that this strategy can work. It remains for future applied investigations to ascertain whether or not this strategy is effective in treating undernutrition in the elderly.

Severe underreporting of energy intake in normal weight subjects: use of an appropriate standard and relation to restrained eating

OBJECTIVE

To assess the influence of different standards and restrained eating on underreporting in healthy, non-obese, weight-stable young subjects.

DESIGN AND SUBJECTS

Eighty-three young adults (20-38 years, 55 women, 28 men) were assessed under weight-stable conditions with a 7-day dietary record and the three-factor eating questionnaire by Stunkard and Messick. Resting energy expenditure (REE; indirect calorimetry) plus data derived from physical activity records (PA) (Standard 1) or REE times an activity factor (AF) (Standard 2) was used as standard for total energy expenditure (TEE). For comparison, doubly labelled water (DLW) was used to measure TEE in a subgroup of subjects.

RESULTS

There was an association between self-reported energy intake and Standard 2 but not with Standard 1. When compared with DLW both calculated standards were inaccurate, but Standard 2 avoided high levels of overreporting. Using Standard 2 to identify 'severe' underreporting (SU; as defined by a deviation of energy intake (EI) and TEE of >20%), SU was seen in 37% of all subjects. It was more frequently found in women than in men (49% of women, 14.3% of men, ). Underreporting subjects had a reduced EI but there were no significant differences in nutritional status (body weight and height, body mass index, fat mass and fat-free mass), energy expenditure and the proportion of energy from macronutrients between normal and underreporting subjects. However, high restraint was associated with a higher degree of underreporting in the total group, whereas disinhibition had an influence only in men.

CONCLUSIONS

A high prevalence of SU is seen in non-obese subjects. Characteristics of eating behaviour (restraint and disinhibition) were associated with underreporting but seemed to have a different influence in men and women.

Diary days needed to estimate activity among older African-American and Hispanic women

PURPOSE

The purpose of this study was to estimate variation in energy expenditure among older African-American and Hispanic female workers and nonworkers, and identify the number of days of diary self-report necessary to reliably estimate activity.

METHODS

227 women (111 African-American, 116 Hispanic) from the Women On The Move study completed a 7-d diary and were used in the analysis for this study (mean age 49.3 yr, SD = 7.0; mean weight 77.0 kg, SD = 17.6 kg; mean BMI 30, SD = 6.5). Kcal per day for total activity and specific types of activity were calculated for each subject and used in generalizability analyses.

RESULTS

Results indicated that 11 d of activity are needed to reliably estimate total activity for African-American nonworkers and 8 d for Hispanic nonworkers. For workers, 12 d of activity are needed to reliably estimate total activity for African-Americans and 14 d are required for Hispanics. Days of diary self-report required by activity type for African-Americans range from 6 to 48 for nonworkers and from 6 to 30 for workers. For Hispanics, days of diary self-report required by activity type range from 8 to 111 for nonworkers and 7 to 42 for workers.

CONCLUSIONS

The results of this study indicate the need for more than 7 d of diary self-report to achieve reliable estimates of total activity in older African-American and Hispanic women. The study also found that certain types of activity could be reliably estimated in less than 7 d. However, when there is less variability in the measure/behavior, the reliability is expected to be less and more measurement days are needed to achieve a desired level of reliability.

Iron and energy supplementation improves the physical work capacity of female college students

A nutritionally controlled study was conducted on two groups of 15 female college students aged 16 to 20 years, selected from Punjab Agricultural University, Ludhiana, Punjab, India. The girls were either anemic (hemoglobin 7.7 g/dl) but energy adequate (AEA), or anemic (hemoglobin 7.4 g/dl) and energy deficient (AED). The AEA group was given iron supplementation (60 mg iron/day) for 6 to 9 months along with 100 mg of ascorbic acid, and the AED group was given iron as well as energy supplementation for 3 months. There was a significant (p < .01) increase in weight, body mass index, mid-upper-arm circumference, and body fat in the AED group after iron-energy supplementation. Hemoglobin, serum iron, transferrin saturation, total iron-binding capacity, and unsaturated iron-binding capacity were below normal in both groups; however, after iron and iron-energy supplementation, there was a significant (p < .01) increase, and these indices were in the normal range. There was a significant (p < .01) increase in exercise time and maximum work load tolerance after iron and iron-energy supplementation. Combined energy and iron deficiency had a greater adverse effect on physical work capacity than energy or iron deficiency alone.

Type A behavior and daily living activity among older minority women

INTRODUCTION

The association between type A behavior pattern (TABP) and physical activity is unclear, with studies reporting both positive and negative results and some reporting no association. Because previous studies have looked primarily at the relationship between TABP and exercise, the purpose of this study was to assess the association between TABP and (1) total activity, (2) activity at work, (3) exercise, (4) household chores, (5) leisure activity, and (6) inactivity.

METHODS

Two hundred twenty-seven women (111 African American, 116 Hispanic) from a larger study (Women on the Move) were used in the analysis for this study. The mean age was 49.3 years (SD 7 years), mean weight 77 kg (SD 17.6 kg), and mean body mass index (BMI) 30 (SD 6.5). As part of the Women on the Move Study, participants completed a 7-day diary and a 10-item Activity Temperament Scale. Multiple regression analysis was conducted to test the relationship between TABP and daily activity. Significant findings were observed for total activity and leisure activity with the Activity Temperament Scale summary score. Both had positive associations, indicating that those who had a higher score on the Activity Temperament Scale also had higher total activity kilocalories (kcal) and leisure activity kilocalories. Significant positive findings were also observed for total activity, leisure activity, and exercise with individual items on the Activity Temperament Scale. Household chores, work, and inactivity had significant negative associations with one or more of the individual items on the Activity Temperament Scale.

CONCLUSIONS

Although previous studies have reported on TABP and physical activity (primarily exercise), these findings provide new information specific to daily living activity by dimension in an older minority population. Results suggest a positive association between TABP and daily living activity with a general pattern of higher scores associated with higher activity and lower scores associated with higher inactivity. However, even though some significant findings were observed, the overall models did not reveal meaningful associations.

Validity of self-reported energy intake in lean and obese young women, using two nutrient databases, compared with total energy expenditure assessed by doubly labeled water

OBJECTIVE

To compare self-reported total energy intake (TEI) estimated using two databases with total energy expenditure (TEE) measured by doubly labeled water in physically active lean and sedentary obese young women, and to compare reporting accuracy between the two subject groups.

DESIGN

A cross-sectional study in which dietary intakes of women trained in diet-recording procedures were analyzed using the Minnesota Nutrition Data System (NDS; versions 2.4/6A/21, 2.6/6A/23 and 2.6/8.A/23) and Nutritionist III (N3; version 7.0) software. Reporting accuracy was determined by comparison of average TEI assessed by an 8 day estimated diet record with average TEE for the same period.

RESULTS

Reported TEI differed from TEE for both groups irrespective of nutrient database (P<0.01). Measured TEE was 11.10+/-2.54 and 11.96+/-1.21 MJ for lean and obese subjects, respectively. Reported TEI, using either database, did not differ between groups. For lean women, TEI calculated by NDS was 7.66+/-1.73 MJ and by N3 was 8.44+/-1.59 MJ. Corresponding TEI for obese women were 7.46+/-2.17 MJ from NDS and 7.34+/-2.27 MJ from N3. Lean women under-reported by 23% (N3) and 30% (NDS), and obese women under-reported by 39% (N3) and 38% (NDS). Regardless of database, lean women reported higher carbohydrate intakes, and obese women reported higher total fat and individual fatty acid intakes. Higher energy intakes from mono- and polyunsaturated fatty acids were estimated by NDS than by N3 in both groups of women (P< or =0.05).

CONCLUSIONS

Both physically active lean and sedentary obese women under-reported TEI regardless of database, although the magnitude of under-reporting may be influenced by the database for the lean women.

SPONSORSHIP

USDA Hatch Project award (ARZT-136528-H-23-111) to LB Houtkooper and WH Howell.

The validity of self-reported energy intake as determined using the doubly labelled water technique

In the 1980s the development of the doubly labelled water (DLW) technique made it possible to determine the validity of dietary assessment methods using external, independent markers of intake in free-living populations. Since then, the accuracy of self-reported energy intake (EI) has been questioned on a number of occasions as under-reporting has been found to be prevalent in many different populations. This paper is a review of investigations using the DLW technique in conjunction with self-reported EI measures in groups including adults, children and adolescents, obese persons, athletes, military personnel and trekking explorers. In studies where a person other than the subject is responsible for recording dietary intake, such as parents of young children, EI generally corresponds to DLW determined energy expenditure. However, in instances where the subjects themselves report their intake, EI is generally under-reported when compared with energy expenditure. It was originally believed that this phenomenon of under-reporting was linked to increased adiposity and body size, however, it is now apparent that other factors, such as dietary restraint and socio-economic status, are also involved. This paper therefore aims to present a more comprehensive picture of under-reporting by tying in the findings of many DLW studies with other studies focusing particularly on the characteristics and mechanisms for under-reporting. Awareness of these characteristics and mechanisms will enable researchers to obtain more accurate self-reports of EI using all dietary recording techniques.

The importance of clinical research: the role of thermogenesis in human obesity

The hypothesis that human obesity is caused by deficient thermogenesis has been proposed by many investigators throughout the 20th century. Supporting evidence was obtained from epidemiologic studies of dietary intake, animal models with aberrant brown adipose tissue (BAT) function, and genetic studies of human polymorphisms of genes involved in BAT function. Supporting evidence was also obtained from clinical studies of the thermogenic effect of meals, but these measures capture only a short portion of the day and may miss some of the thermogenic effect. To capture the effects throughout the day and to move the studies out of the metabolic ward, investigators have used the doubly labeled water (DLW) method to measure total daily energy expenditure. DLW studies have not supported the above hypothesis. Increases in total energy expenditure (TEE) during overfeeding have been small (0.9 +/- 0.8 MJ/d) and account for an average of only 18 +/- 18% of the excess energy intake. Most of this increase is in the resting metabolic rate. Moreover, these studies showed little variation in the changes in resting metabolic rate or in thermogenesis from meals during overfeeding. Instead, the component that is most variable and that accounts for the variability in weight gain during overfeeding is the energy expended in physical activity. This component of TEE deserves greater attention in future studies. These studies of thermogenesis have shown the importance of clinical research as part of a comprehensive approach to understanding the etiology of human obesity.

Eating behavior: lessons from the real world of humans

Food intake by normal humans has been investigated both in the laboratory and under free-living conditions in the natural environment. For measurement of real-world intake, the diet-diary technique is imperfect and tends to underestimate actual intakes but it appears to be sensitive, can detect subtle influences on eating behavior, and produces reliable and valid measures. Research studies in the real world show the multivariate richness of the natural environment, which allows investigation of the complexities of intake regulation, and even causation can be investigated. Real-world research can overcome some of the weaknesses of laboratory studies, where constraints on eating are often removed or missing, facilitatory influences on eating are often controlled or eliminated, the importance of variables can be overestimated, and important influences can be missed because of the short durations of the studies. Real-world studies have shown a wide array of physiologic, psychological, and social variables that can have potent and immediate effects on intake. Compensatory mechanisms, including some that operate with a 2- to 3-d delay, adjust for prior excesses. Heredity affects all aspect of food-intake regulation, from the determination of body size to the subtleties of the individual preferences and social proclivities and the extent to which environmental factors affect the individual. Hence, real-world research teaches valuable lessons, and much more is needed to complement laboratory studies.

Energy expenditure determined by self-reported physical activity is related to body fatness

OBJECTIVE

Activity self-reports are a commonly used tool in assessing daily physical activity (PA) and associated energy expenditure (EE). This study examined the effect of relative body fatness (%BF) on differences between self-reported and measured duration and associated EE in healthy adults.

RESEARCH METHODS AND PROCEDURES

Men and women (n = 115, age 38+/-9 years), ranging in %BF from 7.9% to 58.9%, spent two separate days (normal and exercise) in a whole-room indirect calorimeter where EE was measured. While in the room calorimeter, subjects reported the type, intensity, and duration of each performed PA. The Compendium of Physical Activity was used to calculate the energy cost of each reported activity. The EE of all self-reported activities (EEr) was categorized into four intensity levels, synchronized, and compared with EE from the room calorimeter (EEm).

RESULTS

With increasing %BF, subjects significantly overestimated duration of more strenuous activities (> or =4.5), while underestimating moderate activities (2.5 to 4.4 metabolic equivalents (METs)). Misreporting of duration and/or intensity caused an overestimation or underestimation of PA-associated EE at these levels. Reported EE sleep was lower than measured EE sleep, although both had similar durations. As a result, total EEr was similar to EEm.

DISCUSSION

Individual variability of daily total PA and associated EE generated from self-reports in adults is high. Persons with a higher %BF report duration and/or intensity of moderate to high levels of PA with lower accuracy than leaner individuals. We conclude using the Compendium of Physical Activity is not suitable for the accurate estimation of self-reported EE of AA in adults with a higher %BF.

Interactions between 2H and 18O natural abundance variations and DLW measurements of energy expenditure

Appropriate corrections for 2H and 18O natural abundance are necessary in energy expenditure measurements with the doubly labeled water (DLW) method. The contribution of natural abundance variations to errors in the method is generally ignored if an appropriate dose level is given. Calculation of the appropriate dose level assumes that 2H and 18O natural abundance values are covariant and have a fixed slope. This study has investigated the between- and within-subject natural abundance variations, the latter over periods of time similar to those used in DLW experiment. Although 2H and 18O natural abundance values are covariant between subjects, the slope of their relationship is different from that of the Meteoric Water Line. Within subjects there is no such demonstrable covariance. It is concluded that: 1) the determinants of 2H and 18O natural abundance are different within and between subjects; 2) the concept of an optimal ratio of doses is not valid, and a safer strategy is probably to use a ratio > 10; 3) natural abundance variations may contribute significantly to the magnitude of error in the DLW measurements of energy expenditure.

Precision of DLW energy expenditure measurements: contribution of natural abundance variations

Accuracy and precision of the the doubly labeled water (DLW) measurements of energy expenditure are commonly estimated with models that do not account for 2H and 18O natural abundance variation. A new and simple treatment that completes the ratio-product model is derived in the present study. It uses both linear regression of multipoint data with time and information on within-subject 2H and 18O natural abundance variation. Use of this treatment is demonstrated in a group of seven subjects in whom 2H and 18O natural abundance variation was assessed by collecting predose samples for 6-8 days before dosing. In this set of 16 measurements, the precision (coefficient of variation) of individual DLW estimates of CO2 production was 4.90 +/- 2.14%, of which 3.23 +/- 1.20% arose from natural abundance variation.

Influence of altered body weight on energy expenditure

Long-term metabolic studies indicate that over-feeding underfeeding to gain and lose body weight produce consistent increases and decreases in energy expenditure. These changes occur in both lean and obese subjects and cause deviations from the normal relationship between energy expenditure and metabolic body size. The low energy expenditure/metabolic body size in the reduced obese may contribute to the difficulty in maintaining the reduced body weight.

Limitations in the assessment of dietary energy intake by self-report

Development of the doubly-labeled water method has made it possible to test the validity of dietary intake instruments for the measurement of energy intake. Comparisons of measured energy expenditure with energy intake from either weighed or estimated dietary records against energy expenditure have indicated that obese subjects, female endurance athletes, and adolescents underestimate habitual and actual energy intake. Individual underestimates of 50% are not uncommon. Even in non-obese adults, where bias is minimal, the standard deviation for individual errors in energy intake approaches 20%. Two investigations of the validity of self-reported dietary records for measuring change in dietary intake also indicate large underestimates of the actual change. Because of bias and imprecision, self-reported energy intakes should be interpreted with caution unless independent methods of assessing their validity are included in the experimental design.

Precision and accuracy of doubly labeled water energy expenditure by multipoint and two-point methods

Two-point or multipoint, that is the question. Equations are developed to compare the precision and accuracy of energy expenditure, as estimated from doubly labeled water data, when analyzed by the multipoint and two-point methods. The equations convert the enrichments of deuterium and oxygen-18 into their ratio and product, quantities that are less covariant than the two isotopes themselves are. This is important not only for estimating the precision but also as a graphical aid, since the ratios of the enrichments model carbon dioxide production, whereas the enrichment products largely model water turnover. Using data on 12 human subjects from the United Kingdom and The Gambia as examples, the combined precision and accuracy of the multipoint method (CV 3.6%) was found to be appreciably better than the two-point method (CV 5.4%). The bias in the multipoint estimate of body pool size would need to be three times as large as was observed before it canceled out the better precision.

How accurate is self-reported dietary energy intake?

The measurement of dietary intake by self-report has played a central role in nutritional science for decades. Despite its important role, however, little is known about the accuracy of self-reported intake. Recently, the doubly-labeled water method has been validated for the measurement of total energy expenditure in free-living subjects, and this method can serve as a reference for validating the accuracy of self-reported energy intake. Such comparisons have been made in nine recent studies, and considerable inaccuracy in self-reports of energy intake has been documented. Reported intakes tend to be lower than expenditure and thus are often underestimates of true habitual energy intake. Because the degree of underreporting increases with intake, it is speculated that individuals tend to report intakes that are closer to perceived norms than to actual intake.

Indirect calorimetry: methodological and interpretative problems

The technique of indirect calorimetry is now widely used to examine rates of energy production and substrate oxidation in humans. Although the basic principles of indirect calorimetry are well established, it is important to recognize that there are several potential pitfalls in the methodology and data interpretation that must be appreciated to properly understand and apply the results derived from this technique. In particular, one must recognize that the fundamental measurement provided by indirect calorimetry is the net disappearance rate of a substrate regardless of the metabolic interconversions that the substrate may undergo before its disappearance from its metabolic pool. Under most circumstances, direct oxidation represents the major route by which a substrate disappears from its metabolic pool, and the two terms are often used interchangeably. However, under conditions when rates of gluconeogenesis, ketogenesis, or lipogenesis are elevated, the presumed equivalence between oxidation and disappearance may no longer apply, even though the actual measurements derived from indirect calorimetry remain valid. When indirect calorimetry is combined with other in vivo metabolic techniques (e.g., the insulin clamp or radioisotope turnover methods) it can provide a powerful tool for noninvasively examining complex metabolic processes.