Development and validity assessment of a diet quality index for Australians

Existing Australian diet quality indices have assumed links to health outcomes but their validity for this has not been reported. We extend the features of existing indices for Australian adults by constructing a new diet quality index (Aussie-DQI) using the national dietary guidelines linked to the Australia National Health Priority Areas. Construct validity was assessed using 24 hour dietary recalls from the 1995 National Nutrition Survey (n=10,851 adults aged 19 years and older). Construct and criterion validity were assessed using food frequency questionnaire data from the Nambour Skin Cancer study (n=1355), a community-based longitudinal study with 16 year follow-up and cause-specific mortality outcomes. Generalised linear regression was used to assess associations between Aussie-DQI scores and socio-economic, demographic, health-behaviour characteristics, and food and nutrient intakes, while Cox proportional-hazards modeling was used to assess associations with cancer and allcause mortality. A high Aussie-DQI score was associated with being female, being older, non-smoking status, and BMI in the normal range in both study populations; and Aussie-DQI scores were inversely associated with cancer mortality among men in multivariable-adjusted analyses (hazard ratio = 0.30, 95% CI: 0.11, 0.83; p for trends = 0.06). In conclusion, Aussie-DQI successfully discriminated diet quality and showed that men, younger adults, current smokers and those overweight/obese were less likely to consume foods that meet dietary recommendations; and that a high diet quality is associated with decreased risk of cancer mortality among men. This study adds further evidence to clarify the role of diet quality in decreasing mortality from chronic diseases.