Socioeconomic status, energy cost, and nutrient content of supermarket food purchases

Background: The relative affordability of energy-dense versus nutrient-rich foods may promote socioeconomic disparities in dietary quality and obesity. Although supermarkets are the largest food source in the American diet, the associations between SES and the cost and nutrient content of freely chosen food purchases have not been described. Purpose: To investigate relationships of SES with the energy cost ($/1000 kcal) and nutrient content of freely chosen supermarket purchases. Methods: Supermarket shoppers (n=69) were recruited at a Phoenix AZ supermarket in 2009. The energy cost and nutrient content of participants' purchases were calculated from photographs of food packaging and nutrition labels using dietary analysis software. Data were analyzed in 2010-2011. Results: Two SES indicators, education and household income as a percentage of the federal poverty guideline (FPG), were associated with the energy cost of purchased foods. Adjusting for covariates, the amount spent on 1000 kcal of food was $0.26 greater for every multiple of the FPG, and those with a baccalaureate or postbaccalaureate degree spent an additional $1.05 for every 1000 kcal of food compared to those with no college education. Lower energy cost was associated with higher total fat and less protein, dietary fiber, and vegetables per 1000 kcal purchased. Conclusions: Low-SES supermarket shoppers purchase calories in inexpensive forms that are higher in fat and less nutrient-rich.