Ages 8 to 12 Years: Modeled Data

Percent overweight was a common measure used to describe the entry weights and post-intervention weights of participants in studies of children aged 8–12 years. Percent overweight is calculated as follows: 100% × (actual weight - ideal weight for age, height, & sex) ÷ ideal weight for age, height, & sex. The ideal weight for age, height, and sex was typically taken from a reference dataset such as the World Health Organization's report on the assessment of community nutritional status published in 1966.¹ In a majority of studies conducted in children aged 8–12, the participants were on average 40%–60% overweight prior to the intervention. The average change in percent overweight at the time of the last post-intervention follow-up measurement was -10% to -20%. To model these typical entry weight and results, we have calculated the BMI associated with being 50% overweight (i.e., typical mean entry weight), 40% overweight (i.e., change in percent overweight of -10%), 30% overweight (i.e., change in percent overweight of -20%), and ideal weight. These BMI data were plotted on the gender-specific CDC 2000 BMI-for-age growth charts to visually demonstrate how percentage overweight corresponds to BMI percentiles. The entry BMI that is equivalent to 50% overweight is displayed for ages 8, 10, and 12 years and corresponding -10% and -20% changes in overweight are displayed for ages 9, 11, and 13 years in order to demonstrate that the participants grew older during the course of the study. Plots for boys and girls were similar, therefore we present the data for girls only.

Calculation of age-, height-, and sex-specific BMI based on percent overweight: For ages 8–13, the median height was estimated for each age based on the CDC's 2000 sex-specific stature-for-age growth charts. Ideal weight for height, age, and sex was then taken from the same reference dataset used in several of the original studies.¹ Weight if 50%, 40%, or 30% overweight was determined by multiplying the ideal weight by 1.5, 1.4, or 1.3, respectively. The BMI for each age for each category of % overweight was then calculated as follows: 10,000 × weight in kg ÷ (height in cm)². Data for each age between 8 and 13 years are displayed in Table P-1.

Data from Individual Studies in Adolescents (Figure 5)

For studies that included mostly participants 13 years and older, actual entry weight and outcomes are plotted if these measures were presented using BMI or percentage overweight.²–⁷ One study of participants in this age group⁸ presented triceps skinfold thickness and percentage body fat and is therefore not included in the figure.

In general, the mean entry BMI and post-intervention change in BMI are reported for the treatment group that had the larger decrease in BMI, and these data are plotted at the mean age at entry for the group with the better result. The center of the box symbol corresponds to the entry BMI. The tip of the arrow drawn for each box represents the average change in BMI at the time of the latest post-intervention measurement. Data for plotted values are presented in Table P-2.

Four studies reported actual mean entry BMI and post-intervention BMI.^{3, 5}–⁷ However, only two of these reported both the BMI data and mean entry age stratified by treatment groups.^{3, 7} One study⁵ presents mean entry age for all participants across treatment groups, so the BMI data for the treatment group with the best results (Healthy Habits group) are plotted at that age. One study⁶ presents entry and post-intervention BMI results across treatment subgroups but presents mean age at entry stratified by treatment subgroup. For this study, the BMI data across subgroups are presented in Figure 4 at the age corresponding to the mean of the mean ages presented for each subgroup.

Of the two studies that did not present mean entry BMI and post-intervention BMI, one² presented all age and weight data stratified by treatment subgroups, but the outcomes as percent change in BMI from baseline BMI. In this study, the group that received both sibutramine and behavioral therapy had the better results on average, -8.5% change in BMI from baseline. The actual post-intervention BMI for this treatment group was calculated as follows: mean BMI at entry + (% change in BMI from baseline) × (mean BMI at entry). Entry BMI and post-intervention BMI data were plotted at the mean age at entry for the sibutramine plus behavioral therapy group. The other study⁴ presented entry and post-intervention data as percent overweight. Age and height specific BMI were calculated similar to how they were calculated for the 8 to 12 year old age group using the mean age at entry for the group with the best result. For this study, post-intervention BMI was calculated for a participant 17 years old.