Obesity misclassification and the metabolic syndrome in adults with functional mobility impairments: Nutrition Examination Survey 2003-2006

Abstract

Objectives: The purpose of this study was to estimate the degree of obesity misclassification between body mass index (BMI) and body fat percentage in adults with functional mobility impairment, and to determine cardiometabolic risk profiles.

Methods: Data from the combined 2003-2006 National Health and Nutrition Examination Survey (NHANES) were incorporated. The representative sample included 852 individuals, aged 20-85years, reporting at least one major physical limitation related to mobility or lower body function, and 4724 individuals reporting no impairments. Body mass index, percent body fat (%BF) as determined by dual energy X-ray absorptiometry (DXA), objectively measured sedentary behavior and activity, and markers of cardiometabolic risk were compared between adults with and without functional mobility impairments. Among functional mobility impaired individuals, sensitivity, specificity, and receiver operating characteristic curves were used to evaluate the performance of BMI as a continuous variable, as well as various BMI thresholds to detect obesity defined by sex-specific %BF cutoffs.

Results: Adults with functional mobility impairments were older, had larger waist circumferences (WC), had greater prevalence of obesity according to BMI and %BF, were more sedentary, had less physical activity, and had higher overall cardiometabolic risk. The standard BMI cutoff for obesity had excellent specificity in both men (100%) and women (98.4%) with functional mobility impairment, but sensitivity was poor (<55%). Whereas approximately 36% and 43% of impaired men and women fell into the obese BMI category, over 80% of men and women were obese according to %BF. Individuals with high %BF who were misclassified as not obese, according to BMI, had a significantly higher prevalence of the metabolic syndrome (17.6%) compared to subjects with normal BMI and low %BF (2.1%).

Conclusions: Obesity misclassification and cardiometabolic risk are prevalent among individuals with functional mobility impairments, and thus diagnostic screening for obesity should be modified to account for %BF and/or waist circumference. Behavioral interventions to decrease sedentary behavior, increase activity, and reduce abdominal obesity are warranted.

Keywords: Body composition; Cardiometabolic; Disability; Insulin resistance; Obesity.

Figure 1

Receiver operating characteristic and area under the curve (AUC) values for men (2a) and women (2b) with functional mobility impairments, depicting the performance of BMI as a continuous variable, as well as individual thresholds to detect obesity according to %BF.