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


METHODS
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.


METHODS
Pairs of weight and height measured up to 2.41 years apart used to derive BMI as kg/m2, 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.


CONCLUSIONS
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.
Hunt
Linda P
LP
Department of Endocrinology, Diabetes and Metabolism, Bristol Royal Hospital for Children and University of Bristol, Bristol, UK.
Ford
Anna
A
Sabin
Matthew A
MA
Crowne
Elizabeth C
EC
Shield
Julian P H
JP
D000273:Adipose Tissue / Q000473:pathology; D050154:Adiposity; D000293:Adolescent; D000886:Anthropometry; D001499:Bayes Theorem; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D008954:Models, Biological; D009765:Obesity / Q000473:pathology / Q000503:physiopathology / Q000628:therapy*; D010992:Plethysmography, Impedance; D016896:Treatment Outcome; D015431:Weight Loss