Does diet cost mediate the relation between socioeconomic position and diet quality?

BACKGROUND/OBJECTIVES: Socioeconomic disparities in diet quality are well established. This study tested the hypothesis that such disparities are mediated, in part, by diet cost. SUBJECTS/METHODS: The Seattle Obesity Study (S.O.S.) was a cross sectional study based on a representative sample of 1266 adults of King County, WA conducted in 2008–09. Demographic and socioeconomic variables were obtained through telephone survey. Income and education were used as indicators of socioeconomic position (SEP). Dietary intake data were obtained using a food frequency questionnaire (FFQ). Diet cost was calculated based on retail prices for FFQ component foods. Energy density (KJ/g) and Mean Adequacy Ratio (MAR) were used as two indices of overall diet quality. RESULTS: Higher income and education were each associated with lower energy density and higher MAR scores, adjusting for covariates. Higher income and education were also associated with higher energy adjusted diet cost. Higher quality diets were in turn associated with higher diet costs. All these associations were significant (P<0.0001). In formal mediation analyses, diet cost significantly mediated the pathway between income and diet quality measures, adjusting for covariates (p <0.05 each). Further, income – diet cost – diet quality pathway was found to be moderated by education level. CONCLUSIONS: The social gradient in diet quality may be explained by diet cost. Strategies to improve diet quality among lower socioeconomic strata may need to take food prices and diet cost along with nutrition education into account.