Longitudinal change in diet quality in Australian adults varies by demographic, socio-economic, and lifestyle characteristics.

Knowledge of determinants of change in diet quality is needed, but it is relatively limited to date and mostly available from cross-sectional studies. We investigated longitudinal change in diet quality and its associations with period of birth (birth cohort) and socio-demographic and lifestyle characteristics. We used dietary intake data collected by FFQ in 1992, 1996, and 2007 from a population-based random sample of adults comprising 1511 men and women aged 25-75 y at baseline and applied generalized estimating equations to examine determinants of long-term change in diet quality, calculated using a diet quality index reflecting dietary guidelines for Australian adults. Information on socio-demographic and lifestyle factors was derived from self-reported questionnaires. Multivariable models, stratified by sex, were adjusted for confounders. We showed that there was an overall increase in diet quality in both men and women, but scores related to intake of fruit (men only), cereals, and food variety decreased during a 15-y follow-up. Younger age, higher occupational level (men only), and low to medium level of physical activity and hormone replacement therapy use in women were independently associated with greater improvement in diet quality over time (P < 0.05). In conclusion, despite an overall improvement in diet quality over time, this study suggests that efforts to further improve diet quality in Australia should focus on increasing consumption of fruit, cereals, and a greater variety of foods. More evidence from studies that assess change in dietary quality in longitudinal studies is needed to corroborate these findings.