How do socio-economic status, perceived economic barriers and nutritional benefits affect quality of dietary intake among US adults?

Background: Socio-economic factors may affect diet quality, perhaps differentially across gender and ethnicity. The mechanism of this association is still largely unknown. Objectives: We examined the independent effects of socio-economic status (SES), perceived barrier of food price (PBFP) and perceived benefit of diet quality (PBDQ) on diet quality indicators and indices (DQI_j,k), across gender and ethnicity. Additionally, we estimated the mediation proportion of the effect of SES on DQI_j,k through PBFP and PBDQ. Methods: Data from two cross-sectional surveys, the Continuing Survey of Food Intakes by Individuals (CSFII) and Diet and Health Knowledge Survey (DHKS) 1994-96 were used. Our sample consisted of 4356 US adults aged 20-65 years. With principal components analysis, SES (an index) was measured using household income per capita and education, and PBDQ was measured using an 11-item scale. PBFP was defined as the ratio of importance of food price score relative to nutrition. DQI_j,k were assessed by a set of indicators and two indices including the Healthy Eating Index. Results: The associations between SES, PBFP, PBDQ and DQI_j,k varied significantly across gender and ethnic groups. PBFP acted as a mediator in the association between SES and selected DQI_j indicators, namely energy, fat intake, sodium and simple sugar consumption (mediation proportion >10%), but not PBDQ. Conclusions: SES, PBFP and PBDQ all affect dietary intake, and vary by ethnicity and gender. Positive effect of SES on DQI_j,k may be mediated by PBFP but not PBDQ which is an independent protective factor. Nutrition education is important to promote healthy eating.