Predictors of increasing waist circumference in an Australian population

Objective To identify predictors of increasing waist circumference (WC) over a 5-year period in a contemporary population of Australian adults.Design Longitudinal national cohort of adults participating in the Australian Diabetes, Obesity and Lifestyle Study (AusDiab).Settings Australian adults in 2000 and 2005.Subjects A total of 2521 men and 2726 women aged ≥25 years at baseline who participated in AusDiab and provided anthropometric measurements at baseline (1999–2000) and follow-up (2005).Results A ≥5 % increase of baseline WC occurred in 27 % of men and 38 % of women over the 5-year period. In the multivariate analysis of the total population, there was a higher risk of ≥5 % gain in baseline WC in women, younger people, people with a lower baseline WC, people who never married compared with married/de facto, current smokers compared with never smokers, people with a poorer diet quality and people with a low energy intake. However, there was no significant association with many expected predictors of waist gain such as physical activity. There were some associations between other lifestyle factors and change of WC by sex, age, level of education and across WC categories, but the associations differed across these groups.Conclusions A ≥5 % increase of baseline WC occurred in a significant proportion of men and women over the 5-year period. Of the behavioural factors, poor diet quality was the key predictor of the ≥5 % increase of baseline WC in this cohort. The findings highlight the need to understand better the causal role of lifestyle in regard to increasing WC over time.