ObjectiveTo 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.DesignA cross-sectional study.SettingNational Health and Nutrition Examination Survey, 1999–2006, conducted by the National Center for Health Statistics of the Centers for Disease Control and Prevention.ParticipantsParticipants 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 measuresORs for ABG including pre-diabetes and undiagnosed diabetes (HbA1c ≥5.7%, ≥39 mmol/mol).Results64% 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).ConclusionsIntegrating 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.