Objective: To describe the relationship between two measures of body fat and selected non-fatal health conditions in the New Zealand adult population in 2003.

Method: Data were obtained from the 2002/03 New Zealand Health Survey. A total of 10,026 adults aged 25 years and over were classified according to measured body mass index (BMI) and waist circumference (WC). BMI classes were 18.5–24.9, 25.0–29.9, 30.0–34.9, geqslant R: gt-or-equal, slanted35.0 kg/m2. WC classes were <94, 94–102, >102 centimetres (cm) for males and <80, 80–88, >88 cm for females. Prevalence rate ratio estimates for selected self-reported health conditions were calculated for males and females separately, adjusting for age, ethnicity, deprivation and smoking using logistic regression.

Results: Increasing BMI or WC class was associated with increasing prevalence of cardiovascular disease, diabetes, high blood pressure, high blood cholesterol, osteoarthritis, asthma and sleep disorders in both males and females. The association with depression was not statistically significant in either gender. Associations were strongest for diabetes and blood pressure, with adults in the highest BMI or WC class at least 3.5 times more likely to have diabetes and 2–3 times more likely to have high blood pressure compared with those in the lowest classes.

Conclusions: Increasing body fatness, defined by either BMI or WC, was associated with increased prevalence of many important health conditions. If the obesity epidemic is not halted or reversed, the impact on both the New Zealand population and health system will be considerable.