The relationship between body mass index and waist circumference: implications for estimates of the population prevalence of overweight

OBJECTIVE: Body mass index (BMI) based on self-reported height and weight is a systematically biased, but acceptable measure of adiposity and is commonly used in population surveys. Recent studies indicate that abdominal obesity is more strongly associated with obesity-related health problems than is adiposity measured by BMI. The purpose of this study was to determine the relationships of both measured and self-reported BMI with measured waist circumference in a randomly selected sample of Australian adults. DESIGN: Cross-sectional survey with self-reported and laboratory-based measures of adiposity. SUBJECTS: 1140 randomly-selected Australian adults aged 18-78 y resident in the city of Adelaide, South Australia. MEASUREMENTS: Data on self-reported and measured height and weight as well as measured waist circumference were drawn from the Pilot Survey of the Fitness of Australians database. The proportion of men and women with acceptable BMI (BMI/=94 cm for men and >/=80 cm for women) was determined. Differences in the prevalence of overweight based on BMI alone or BMI and waist circumference were also determined. RESULTS: Compared with the prevalence based on self-reported BMI alone, the prevalence of overweight among men based on self-reported BMI and waist circumference combined was 2.4%, 5.3%, 19.1% and 7.5% greater for men aged 18-39 y, 40-59 y, 60-78 y and for all men, respectively. Among women, compared with the prevalence based on self-reported BMI alone, the prevalence of overweight based on the combined measures was 9.9%, 24.0%, 33.3% and 20.6% greater for women aged 18-39 y, 40-59 y, 60-78 y and for all women, respectively. CONCLUSIONS: If waist circumference is used as the criterion, then the prevalence of overweight among Australian adults, and probably other Caucasian populations, may be significantly greater than indicated by surveys relying on self-reported height and weight. The development of valid self-reported measures of waist circumference for use in population surveys may allow more accurate epidemiological monitoring of overweight and obesity.