Informational value of percent body fat with body mass index for the risk of abnormal blood glucose: a nationally representative cross-sectional study

OBJECTIVE: To examine the value of percent body fat (%BF) with body mass index (BMI) to assess the risk of abnormal blood glucose (ABG) among US adults who are normal weight or overweight. We hypothesised that normal-weight population with higher %BF is more likely to have ABG. DESIGN: A cross-sectional study. SETTING: National Health and Nutrition Examination Survey, 1999–2006, conducted by the National Center for Health Statistics of the Centers for Disease Control and Prevention. PARTICIPANTS: Participants were US adults aged 40 and older who have never been diagnosed with type 2 diabetes by a doctor (unweighted n=6335, weighted n=65 705 694). The study population was classified into four groups: (1) normal weight with normal %BF, (2) normal weight with high %BF, (3) overweight with normal %BF and (4) overweight with high %BF. MAIN OUTCOME MEASURES: ORs for ABG including pre-diabetes and undiagnosed diabetes (HbA1c ≥5.7%, ≥39 mmol/mol). RESULTS: 64% of population with normal BMI classification had a high %BF. Prevalence of ABG in normal-weight group with high %BF (13.5%) is significantly higher than the overweight group with low %BF (10.5%, P<0.001). In an unadjusted model, the OR of ABG was significantly greater in adults at normal BMI with high %BF compared with individuals at normal weight with low %BF. In an adjusted model controlling for age, sex, race/ethnicity, first-degree-relative diabetes, vigorous-intensity activities and muscle strengthening activities, risks of ABG were greater in population with normal weight and high %BF (OR 1.55, 95% CI 1.01 to 2.38) and with overweight and low %BF (OR 1.17, 95% CI 0.69 to 1.98, P<0.05). CONCLUSIONS: Integrating BMI with %BF can improve in classification to direct screening and prevention efforts to a group currently considered healthy and avoid penalties and stigmatisation of other groups that are classified as high risk of ABG.