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 DQIj, k may be mediated by PBFP but not PBDQ which is an independent protective factor. Nutrition education is important to promote healthy eating.