Do nutrition knowledge and beliefs modify the association of socio-economic factors and diet quality among US adults?

Objectives: We examined effects of socio-economic status (SES) factors on diet quality and fruits and vegetables intake among US adults and effect modification by nutrition knowledge and beliefs. Methods: We used national cross-sectional data (Continuing Survey of Food Intake by Individuals) on 4356 US adults, aged 20-65 years, collected in 1994-1996. Socio-economic factors considered were education and poverty income ratio. Nutrition knowledge and belief score was measured by principal components analysis of 11 question responses. We considered three binary and two continuous outcomes related to United States Department of Agriculture recommended intake of fruits and vegetables and overall diet quality through Healthy Eating Index and alternate Mediterranean Diet Score. Results: Multivariate analyses indicated that better SES independently improved likelihood of adequate fruits and vegetables intake and overall diet quality. In several cases, nutrition knowledge and beliefs acted as an effect modifier. In particular, education showed no association with diet quality among subjects in the lowest nutrition knowledge and belief tertile, while the association was consistently stronger in the highest tertile (Education × Nutrition knowledge and beliefs interaction term P < 0.10 for Healthy Eating Index and both fruits and vegetables guidelines). A similar interaction was noted for poverty income ratio. Conclusion: For improvement in overall diet quality, socio-economic interventions must be coupled with health education programs targeting all segments of the US population.