Predictors of change in weight and waist circumference: 15-year longitudinal study in Australian adults.

Background/objectives: This study examines which socio-demographic and lifestyle characteristics are associated with weight and waist circumference (WC) change in a cohort of Australian adults over a 15-year period (1992-2007). Further, it tests the effect of period of birth (birth cohort) on mean weight and WC at two time points, 15 years apart.

Subjects/methods: Up to three repeated measures of weight (n=1437) and WC (n=1317) were used. Self-reported data on socio-demographic and lifestyle characteristics were derived from repeated questionnaires. Multivariable models, stratified by sex, were adjusted for potential confounders.

Results: Participants born more recently were heavier, on average, than those in the same age group 15 years earlier, but there was no such secular trend in WC. Age at baseline was associated with change in weight and WC, but the pattern was different: participants gained weight up to age 55 years, while WC gain continued to 65 years. In women, higher level of recreational physical activity was associated with lower WC gain (P<0.05). Parity was also associated with WC change in women (P<0.05), but there was no linear trend.

Conclusions: Age was the most important factor associated with change in weight and WC in both sexes, apparently reducing the influence of all potential covariates. Among women, physical activity and parity were also associated with change in weight and WC. This study provides longitudinal evidence to support public health efforts that address the continuous increases in average weight and WC of many populations around the world.