William H. Dietz

Energy cost of physical activities in 12-y-old girls: MET values and the influence of body weight

BACKGROUND: Few data exist on the energy cost of specific activities in children. The influence of body weight on the energy cost of activity when expressed as metabolic equivalents (METs) has not been vigorously explored.OBJECTIVE: To provide MET data on five specific activities in 12-y-old girls and to test the hypothesis that measured MET values are independent of body weight.SUBJECTS AND METHODS: In 17 12-y-old girls, resting metabolic rate (RMR) and the energy expended while sitting, standing, walking on a flat treadmill at 3.2 and at 4.8 km/h, and walking on a treadmill at a 10% incline at 4.8 km/h were measured using indirect calorimetry. MET values were calculated by dividing the energy expenditure of an activity by the subjects RMR. The influence of body weight was assessed using simple linear regression.Results: The observed METs were more consistent with published values for similar activities in adults than those offered for children. Body weight was a statistically significant predictor of the MET of all three walking activities, but not the MET of sitting or standing. Body weight explained 25% of the variance in the MET value for walking at 3.2 km/h, 39% for walking at 4.8 km/h, and 63% for walking at a 10% incline at 4.8 km/h.CONCLUSION: METs for the three walking activities were not independent of body weight. The use of average MET values to estimate the energy cost of these three activities would result in an underestimation of their energy cost in heavier girls and an overestimation in lighter girls. These results suggest that the estimation of total energy expenditure from activity diary, recall, and direct observation data using average MET values may be biased by body weight.

Obesity in infants, children, and adolescents in the United States I. Identification, natural history, and aftereffects

Abstract This review examines the indentification, natural history and after-effects of obesity in children and adolescents in the United States. Although the use of the triceps skinfold to establish the diagnosis of obesity is widely accepted, a precise relationship of excessive adiposity with morbidity has not yet been clearly established. Available epidemiologic studies suggest a uniform incidence of the disease throughout childhood and adolescence. The aftereffects of obesity include effects on growth, psychological dysfunction, orthopedic disorders, hypertension, and maturity onset diabetes mellitus. An important but neglected concept in the study of obesity is the potentially synergistic metabolic abnormaliites induced by the disease which may contribute to its persistence.

Relationship between temperament, nonresting energy expenditure, body composition, and physical activity in girls

Objectives: To assess the extent that predilection for movement, as measured by a temperament questionnaire (activity temperament), contributes to nonresting energy expenditure and body composition in girls.Design, Setting, and Participants: Baseline data for 196 premenarcheal non-obese girls aged 8–12 y were obtained from a longitudinal study of growth and development. The association of activity temperament with nonresting energy expenditure in girls with low and high levels of physical activity was evaluated, as was the association of activity temperament with body composition.Measures: Maternal reports of child activity temperament were obtained by questionnaire. Nonresting energy expenditure was calculated as total energy expenditure (measured by doubly labeled water) minus resting energy expenditure (obtained by indirect calorimetry). Body composition was estimated by total body water. Questionnaires and activity diaries were used to assess physical activity and sedentary behavior.Results: Higher activity temperament was associated with higher nonresting energy expenditure after multivariate control for weight, vigorous activity, walking and light activity, and television viewing, although activity temperament did not account for a large percentage of the variability in nonresting energy expenditure (partial squared correlation coefficient=0.03). In girls with physical activity levels below the median, high activity temperament was associated with a mean±s.d., nonresting energy expenditure of 310±138 kJ (74±33 kcal) above that of girls with a low activity temperament. Girls with a high activity temperament had less body fat than did girls with a low activity temperament (21.6 vs 24.5%, a difference of 2.9 percentage points; 95% confidence interval, 1.3–4.4 percentage points).Conclusion: Predilection for movement, as measured by a temperament questionnaire, contributes to nonresting energy expenditure and may be useful in capturing an aspect of energy expenditure in population studies. The cross-sectional observation that girls with a high activity temperament were leaner than girls with a low activity temperament suggests that a constitutional predilection for movement may play a role in the development of obesity.

Body fatness and bioelectrical impedance in non-obese pre-menarcheal girls: comparison to anthropometry and evaluation of predictive equations

Objectives: To determine in non-obese pre-menarcheal girls if bioelectrical impedance (BIA) is a better predictor of body fatness than triceps skinfold (TSF) or body mass index (BMI) and to cross-validate published equations for determination of fat-free mass (FFM) from BIA in pre-menarcheal girls. Design: Cross-sectional analysis of data from 132 non-obese pre-menarcheal girls. The relationship of percent body fat (%BF), derived from isotopic dilution of H218O to TSF, BMI, and %BF by BIA, calculated from measures of height, weight and resistance was examined by correlation analysis. Setting: Massachusetts Institute of Technology (MIT) Clinical Research Center in Cambridge, MA, USA. Subjects: Pre-menarcheal girls aged 8–12 y were recruited from local schools, MIT summer day camp and by word of mouth. Results: TSF accounted for 68% of the explained variance (R2) in the prediction of %BF measured by H218O, compared to 38% for BMI and 70% for BIA. Prediction of FFM by comparison of published equations was evaluated in this population. The predictive ability differed by Tanner stage. Kushner’s equation (Kushner et al, 1992), based solely on height2/resistance was the only equation that provided estimates that did not differ significantly from measured values among all Tanner stages. Conclusions: BIA appears to be a valid and reliable measure of FFM but is no better than TSF in predictions of body fat. Sponsorship: Studies were conducted at the General Clinical Research Center at MIT and were supported by NIH grants RR-00088, DK-HD50537, and DK46200.

Obesity in infants, children, and adolescents in the united states II. causality

Abstract Investigations of the causality of obesity are broadly divided into host and environmental categories. Among host characteristics, age, sex and race appear to have no consistent effect on the prevalence of obesity among children in the United States. Reduced thermogenesis may enhance susceptibility to obesity, but the onset of the disease reflects energy intakes in excess of expenditure. Clinical conditions causing impaired regulation of energy balance are rare. The multiple environmental variables associated with obesity, primarily those within families, suggest that the factors that promote excessive energy intake for expenditure are behavioral. Although definitive proof of a causal relationship is lacking, these data suggest that the origins of obesity are environmental.

Nutritional status of poor black and hispanic children in an urban neighborhood health center

Abstract A survey was made of a poor inner-city population attending a neighborhood health center to determine the prevalence of undernutrition, obesity, and short stature. The Waterlow classification of acute and chronic undernutrition was used; obesity was defined as triceps fat fold 85%ile. A total of 316 patients aged 0–12 years were studied; 69% were Hispanic and 29% were Black. The prevalence of undernutrition was 14%, whereas only 11% were obese. Short stature was found in 21%. There were no significant differences between Blacks and Hispanics in the prevalence of undernutrition, obesity, and short stature. Hispanic immigrant children had significantly more short stature than U.S. born Hispanics. These data indicate a prevalence of undernutrition in some U.S. population that is comparable to that in developing countries.

Obesity in infants, children, and adolescents in the united states III. Therapy and prevention: Individual, family, and community

Abstract The management of obesity in children and adolescents has not received intensive investigation. Attempts at modifying behavior have had only limited success; published results have been biased by voluntary participation in controlled studies, by use of highly restrictive diets, and by the study of children with lesser degrees of obesity. A major difficulty in the evaluation of more radical therapies, such as surgery or highly restrictive diets, is that the risks of therapy must be balanced against the risks of continuing disease. Information on both is sparse. Review of the epidemiologic variables associated with obesity suggests that family factors have a significant effect on both the onset and course of the disease. Family therapy therefore deserves more critical evaluation.