Clinical measures of adiposity and percentage fat loss: which measure most accurately reflects fat loss and what should we aim for?

Abstract

Objective: To determine which clinical measure of childhood obesity should be monitored to best reflect change in adiposity in a weight management programme and estimate the degree of change needed to be relatively certain of fat reduction. Subjects: 92 obese children with a mean (range) age of 12.8 (6.9-18.9) years and a mean body mass index standard deviation score (BMI SDS) of +3.38 (+2.27 to +4.47) attending a hospital-based clinic on a regular, 3 monthly basis. Measurements: Pairs of weight and height measured up to 2.41 years apart used to derive BMI as kg/m 2 , and adjusted for age and gender to give weight and BMI SDS (BMI-z score) using British 1990 Growth Reference Data. Contemporaneous adiposity estimated by fatness measured by a bioimpedance segmental body composition analyser. Results: Changes in BMI-z scores, compared to BMI, weight and weight SDS, most accurately reflected loss of fat. Reductions of 0.25, 0.5, 0.75, and 1 BMI SDS equate to expected mean falls in total body fat percentage of 2.9%, 5.8%, 8.7% and 11.6%. Approximate 95% prediction intervals indicated that a fall in BMI SDS of at least 0.6 over 6-12 months (or 0.5 over 0-6 months) is consistent with actual fat loss. Conclusion: Change in BMI-z score best reflects percentage fat loss compared to BMI, weight and weight SDS. The wide variation in likely percentage fat loss for a given BMI SDS reduction means a loss of 0.5-0.6 is required to be relatively certain of definite percentage fat reduction.

An Adaptation of Family-Based Behavioral Pediatric Obesity Treatment for a Primary Care Setting: Group Health Family Wellness Program Pilot

“…Mean improvement in child Z-BMI was comparable with group family-based treatment interventions in the extant literature 13,[24][25][26] and was above the threshold for clinically meaningful improvement. 27 In addition, change in child quality of life reflected clinically meaningful improvement. The proportion of children with significantly impaired quality of life 23 dropped by half from before to after treatment.…”

Evidence Update on the Treatment of Overweight and Obesity in Children and Adolescents

“…Cutoffs for clinical significance have been suggested in the literature for BMI z score (e.g., 0.25 or 0.5 decrease; Ford, Hunt, Cooper, & Shield, 2010;Hunt, Ford, Sabin, Crowne, & Shield, 2007;Reinehr & Andler, 2004), and %OW (7 percentage point decrease; TODAY Study Group, 2012), however, further research is needed to define the degree of change in these outcomes that produces clinically meaningful effects in the short term, and their long-term sustainability.…”

“…Provides the simplest substitute measure of percentage loss in adiposity . Attenuates change for heavier children (i.e., as children become heavier they will show less change in treatment) (Cole et al, 2005;Hunt et al, 2007; BMI-SDS No. of SD units above or below the median based on statistically derived curves.…”

Randomised controlled trial evaluating the effectiveness and cost-effectiveness of ‘Families for Health’, a family-based childhood obesity treatment intervention delivered in a community setting for ages 6 to 11 years

“…21 A concern was raised that MEND had the potential to widen ethnic and socioeconomic inequalities in the outcome of BMI. A further question is whether or not a mean change of -0.18 is making a sufficient population impact, when a clinically significant change in individuals is considered a reduction in BMI z-score, of at least -0.5, which results in a reduction in cardiovascular risk and improved insulin resistance, 110,111 although others suggest a reduction of 0.25 as the minimum clinically effective change. 65 So, even when interventions work, they may have only a limited impact on the number of children who move to a healthy weight.…”