Prospective associations between diet quality and body mass index in disadvantaged women: the Resilience for Eating and Activity Despite Inequality (READI) study.

Background: Dietary patterns that align with recommended guidelines appear to minimize long-term weight gain in the general population. However, prospective associations between diet quality and weight change in disadvantaged adults have not been examined. This study examined associations between concurrent change in diet quality and body mass index (BMI) over 5 years among women living in socioeconomically disadvantaged neighbourhoods. Methods: Dietary intake and BMI were self-reported among 1242 women living in disadvantaged neighbourhoods in Victoria, Australia, at three time points from 2007/08 to 2012/13. Diet quality was evaluated using the Australian Dietary Guideline Index (DGI). Associations between concurrent change in diet quality and BMI were assessed over the three time points using fixed effects and mixed models. Models were adjusted for age, smoking, menopausal status, education, marital status, number of births, urban/rural location and physical activity. Results: Average BMI increased by 0.14 kg/m2 per year increase in age in the fixed effects model, and by 0.13 kg/m2 in the mixed model (P < 0.0001). BMI decreased by 0.014 kg/m2 for a woman of average age with each unit increase in DGI score in the fixed effects model (p < 0.0001), and by 0.012 kg/m2 in the mixed model (P = 0.001). The rate of change in BMI with age was greater for those with a lower DGI score than for those with a higher score (P < 0.10). Conclusions: Positive change in diet quality was associated with reduced BMI gain among disadvantaged women. Supporting disadvantaged women to adhere to population-level dietary recommendations may assist them with long-term weight management.