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Clinical measures of adiposity and percentage fat loss: which measure most accurately reflects fat loss and what should we aim for?
  1. Linda P Hunt*,
  2. Anna Ford*,
  3. Matthew A Sabin,
  4. Elizabeth C Crowne,
  5. Julian P H Shield
  1. Department of Endocrinology, Diabetes and Metabolism, Bristol Royal Hospital for Children and University of Bristol, Bristol, UK
  1. Correspondence to:
    Dr J Shield
    Bristol Royal Hospital for Children, Upper Maudlin St, Bristol BS2 8AE, UK;j.p.h.shield{at}bristol.ac.uk

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/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.

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.

  • AIC, Akaike information criterion
  • BMI, body mass index
  • IOTF, International Obesity Task Force
  • MCMC, Markov chain Monte Carlo
  • PI, prediction interval
  • SDS, standard deviation score
  • BMI-z scores
  • adiposity
  • bio-impedance
  • obesity

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Footnotes

  • * Both authors contributed equally to this work.

  • Published Online First 29 January 2007

  • Competing interests: None.

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