Longitudinal changes in energy expenditure in girls from late childhood through midadolescence.

BACKGROUND: Longitudinal data on energy expenditure in children and adolescents are scarce. OBJECTIVE: The purpose of this study was to examine changes in energy expenditure and physical activity in girls from late childhood through midadolescence. DESIGN: We measured total energy expenditure (TEE) by doubly labeled water, resting metabolic rate (RMR) by indirect calorimetry, body composition by 18O dilution, and time spent in activity by an activity diary in 28 initially nonobese girls at approximately 10, approximately 12, and approximately 15 y of age. Changes with age in TEE, RMR, and activity energy expenditure (AEE), both in absolute terms and in adjusted analyses, and in physical activity level (PAL) and time spent sleeping, being sedentary, and in moderate and vigorous activity were evaluated by mixed-model repeated-measures analyses. RESULTS: Absolute TEE and AEE increased significantly from age 10 to age 15 y (P < 0.0001 for both). Absolute RMR at ages 12 and 15 y did not differ significantly, despite significant increases in fat-free mass and fat mass between the visits. PAL was significantly higher (P < 0.0001) at age 15 y than at age 10 or 12 y, whereas time spent being sedentary increased significantly from age 10 to age 15 y (P < 0.001), and AEE adjusted for fat-free mass appeared to decrease over the same interval. CONCLUSION: Conclusions drawn regarding changes with age in physical activity depend on the measure of physical activity assessed.

Does menarche mark a period of elevated resting metabolic rate?

Resting metabolic rate (RMR) and body composition were measured in 44 initially nonoverweight girls at three time points relative to menarche: premenarche (Tanner stage 1 or 2), menarche (+/-6 mo), and 4 yr after menarche. Mean absolute RMR was 1,167, 1,418, and 1,347 kcal/day, respectively. Absolute RMR was statistically significantly higher at menarche than at 4 yr after menarche despite statistically significantly less fat-free mass (FFM) and fat mass (FM), suggesting an elevation in RMR around the time of menarche. The pattern of change in RMR, adjusted for FFM, log transformed FM, age, race, parental overweight, and two interactions (visit by parental overweight, parental overweight by FFM), was also considered. Adjusted RMR did not differ statistically between the visits for girls with two normal-weight parents. For girls with at least one overweight parent, adjusted RMR was statistically significantly lower 4 yr after menarche than at premenarche or menarche. Thus parental overweight may influence changes that occur in RMR during adolescence in girls.

Longitudinal changes in the accuracy of reported energy intake in girls 10-15 y of age.

BACKGROUND: Dietary records are often used to estimate individual energy needs and population energy requirements. However, significant underreporting of total energy intake (EI) has been found when EI is compared with total energy expenditure (EE) measured by doubly labeled water. OBJECTIVE: This study aimed to determine whether the accuracy of reported EI decreases from middle childhood to adolescence. DESIGN: In this longitudinal study of 26 healthy girls, EI and EE were measured at ages 10, 12, and 15 y. Accuracy of reported EI (EI/EE x 100%) was calculated at each age. At study entry, girls had a mean (+/- SD) body mass index (in kg/m(2)) of 16.8 +/- 1.9 and percentage body fat of 24.0 +/- 4.6%. Measurements of EI were a 7-d dietary record and those of EE were by doubly labeled water. RESULTS: As they got older, girls tended to report EI less accurately: the average accuracy was 88 +/- 13% at age 10 y, 77 +/- 21% at age 12 y, and 68 +/- 17% at age 15 y. The declines in reporting accuracy from age 10 y to age 12 y and from age 10 y to age 15 y were statistically significant (P = 0.03 and P = 0.001, respectively). Reporting accuracy also declined from age 12 to age 15 y but not significantly. When percentage body fat was added to the model, results were essentially unchanged. CONCLUSION: Because of the decline in EI reporting accuracy with age, the use of EI data obtained from dietary records in adolescent girls will result in substantial underestimation of energy needs.

Relation of body composition, parental overweight, pubertal stage, and race-ethnicity to energy expenditure among premenarcheal girls.

BACKGROUND: Previous studies assessed the influence of parental weight status, sexual maturation, race-ethnicity, and energy expenditure among children, but few examined these issues comprehensively. OBJECTIVE: The objective was to determine whether differences in energy expenditure among premenarcheal girls are related to the pubertal stage and the race-ethnicity of the girls or to the weight status of their parents. DESIGN: We measured the body composition and the energy expenditure of 196 nonobese girls enrolled in a longitudinal study. Total body water was measured by the isotopic dilution of (18)O water. We measured resting metabolic rate with the use of indirect calorimetry and daily energy expenditure by the doubly labeled water method. We used established criteria to determine sexual maturation. Parental weight status was based on body mass index. RESULTS: Resting metabolic rate was higher among girls with >or=1 overweight parent than among girls with 2 normal-weight parents. Total energy expenditure was also higher among girls with >or=1 overweight parent, but these results were of borderline significance. We found no effect of pubertal stage on resting metabolic rate. Nonresting energy expenditure was significantly lower among pubertal girls than among prepubertal girls. After adjustments for age and body composition, we noted that resting metabolic rate, nonresting energy expenditure, and total energy expenditure were all significantly lower among black girls than among white girls. CONCLUSIONS: Differences in resting metabolic rate and total energy expenditure among premenarcheal girls were associated with parental weight status and the girls' race-ethnicity, whereas differences in nonresting energy expenditure were associated with pubertal stage and race-ethnicity. Whether the observed differences in energy expenditure persist after puberty and predict weight gain during puberty awaits the results of longitudinal analyses.