Aerobic fitness, not energy expenditure, influences subsequent increase in adiposity in black and white children

Energy expenditure, physical activity, and obesity in children

Although there are physiologic and genetic influences on the various components of energy metabolism and body weight regulation, and a major portion of individual differences in body weight can be explained by genetic differences, it seems unlikely that the increased global prevalence of obesity has been driven by a dramatic change in the gene pool. It is more likely and more reasonable that acute changes in behavior and environment have contributed to the rapid increase in obesity and that genetic factors may be important in the deferring individual susceptibilities to these changes. The most striking behavioral changes that have occurred have been an increased reliance on high-fat and energy-dense "fast foods," with larger portion sizes, coupled with an ever-increasing sedentary lifestyle. The more sedentary lifestyle is caused by an increased reliance on technology and labor-saving devices, which has reduced the need for physical exertion for everyday activities. Examples of energy-saving devices that have resulted in a secular decline in physical activity include: Increased use of automated transport rather than walking or biking Central heating and use of automated equipment, such as washing machines, in the household. Reduction in physical activity in the workplace because of computers, automated equipment, and electronic mail. Increased use of television and computers for entertainment and leisure activities. Use of elevators and escalators rather than stairs. Increased concern for crime, which has reduced the likelihood of outdoor playing. Poor urban planning that does not provide adequate biking paths or even sidewalks in some communities. Thus, the increasing prevalence, numerous health risks, and astounding economic costs of obesity clearly justify widespread efforts toward prevention efforts. These prevention efforts should begin in childhood because the behaviors are learned and continue through the lifetime.

A longitudinal study of resting energy expenditure relative to body composition during puberty in African American and white children

BACKGROUND

Body composition and resting energy expenditure (REE) have not been examined longitudinally during puberty.

OBJECTIVE

The purpose of this longitudinal study was to examine the influence of pubertal maturation on REE relative to body composition in African American and white children.

DESIGN

The study included 92 white and 64 African American children (mean age at baseline: 8.3 and 7.9 y, respectively) from Birmingham, AL. The children had 2-5 annual measurements of fat mass (FM), lean mass (LM), and REE. The Tanner stages of the children ranged from 1 to 5. Mixed-model repeated-measures analyses were used to test the change in REE relative to body composition with increasing Tanner stage among ethnic and sex groups.

RESULTS

LM increased from Tanner stage 1 to subsequent stages. FM relative to LM decreased from Tanner stage 1 to stages 3, 4, and 5 but not from stage 1 to stage 2. The African American children had relatively higher limb LM and lower trunk LM than did the white children. REE declined with Tanner stage after adjustment for ethnicity, sex, FM, and LM. This decline was significant from Tanner stage 1 to stages 3, 4, and 5 but not to Tanner stage 2. After adjustment for age, Tanner stage, FM, and LM or LM distribution, REE was significantly higher in white than in African American children (by approximately 250 kJ/d).

CONCLUSION

In a large sample of children at various Tanner stages, we found an ethnic difference in REE after adjustment for age, Tanner stage, FM, and LM that was not explained by the difference in LM distribution.

Metabolic precursors and effects of obesity in children: a decade of progress, 1990-1999

Current data suggest that 20% of US children are overweight. An analysis of secular trends suggested a clear upward trend in body weight in children of 0.2 kg/y between 1973 and 1994. In addition, childhood obesity is more prevalent among minority subgroups, such as African Americans. Obesity that begins early in life persists into adulthood and increases the risk of obesity-related conditions later in life. Obesity is now considered a disease of epidemic proportions, not just in the United States but also worldwide. In the past 10 y there has been a tremendous increase in the number of studies examining the etiology and health effects of obesity in children. The major objectives of this article are to 1) review highlights in pediatric obesity research from 1990 to 1999; 2) summarize our research on the roles of energy expenditure, physical activity, and aerobic capacity in the etiology of pediatric obesity, and on ethnic differences in the relation between obesity and type 2 diabetes risk factors in children; and 3) discuss areas of future study that will require greater emphasis as the field of childhood obesity research evolves over future years.