Body Mass Index Underestimates Adiposity in Persons With Multiple Sclerosis

ObjectivesTo examine the relation between body mass index (BMI) and adiposity assessed by dual-energy x-ray absorptiometry in persons with multiple sclerosis (MS) and non-MS controls as well as to determine the accuracy of standard and alternate BMI thresholds for obesity.DesignCross-sectional.SettingUniversity research laboratory.ParticipantsThe sample included persons with MS (n=235) and controls (n=53) (N=288).InterventionsNot applicable.Main Outcome MeasuresMain outcome measures included BMI, whole body soft tissue composition (ie, percent body fat [%BF], fat mass, and lean soft tissue mass), bone mineral content, and bone mineral density.ResultsWe observed significant strong associations between BMI and sex-specific %BF in persons with MS and non-MS controls, and BMI explained ∼40% of the variance in %BF in both MS and control samples. Receiver operating characteristic curve analyses indicated that the standard BMI threshold for obesity (ie, 30kg/m2) had excellent specificity (93%–100%) but poor sensitivity (37%–44%) in persons with MS and non-MS controls. The BMI threshold that best identified %BF-defined obesity was 24.7kg/m2 in the MS sample and 25.1kg/m2 in the control sample.ConclusionsWe determined a strong association between BMI and adiposity; however, the current BMI threshold for classifying obesity underestimates true adiposity in persons with MS. A similar relation was observed between BMI and obesity in non-MS controls. The non-MS sample included primarily middle-aged women, and similar BMI-%BF misclassifications have been reported in these samples.