For convenience, health practitioners and clinicians are inclined to classify people/patients as overweight or obese based on body mass index (BMI) cut-off points of 25 and 30 kg/m^2 respectively, irrespective of age and gender.
PURPOSE: To identity whether, for the same levels of adiposity, BMI is the same across different age groups and gender.
METHODS: A random sample of 4316 healthy participants were selected, aged 16 years and over, from thirty English parliamentary constituencies. A sub-sample took part in a physical appraisal yielding BMI (kg/m^2) and estimates of BF% data for 2993 healthy people (male n=1420; female n=1573). Estimates of BF% were determined using the methods based on skin fold thicknesses at four sites; the biceps, triceps, sub-scapular and supra-iliac.
RESULTS: A two-way ANCOVA revealed significant differences in BMI between different age groups and gender (plus an interaction), using body fat (%) as the covariate. Younger males in their 20’s had greater BMI’s (by 4 kg/m^2) than older males in their 50’s for the same levels of adiposity. Similarly, younger females in their 20’s had greater BMI’s (by 3 kg/m^2) than females in their 50’s also for the same levels of adiposity.
CONCLUSIONS: If BMI thresholds for overweight (BMI=25 kg/m2) and obese (BMI=30 kg/m2) are to reflect the same levels of adiposity across all gender and age groups within a population, age- and gender-specific BMI adjustments outlined above are necessary to more accurately/fairly reflect the same critical levels of adiposity.