Body Mass Index Underestimates Adiposity in Persons With Multiple Sclerosis.

OBJECTIVES

To 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.

DESIGN

Cross-sectional.

SETTING

University research laboratory.

PARTICIPANTS

The sample included persons with MS (n=235) and controls (n=53) (N=288).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Main 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.

RESULTS

We 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/m(2)) 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/m(2) in the MS sample and 25.1kg/m(2) in the control sample.

CONCLUSIONS

We 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.