Fixed Costs, Failing Diets: Shopping Frequency and Food Choice

Abstract

From 1998 to 2009 I find that the average time between U.S. households’ grocery shopping trips has steadily increased from 4.7 to 6.2 days, and from 1998 to 2006 per capita monthly consumption of fresh fruits and vegetables has decreased from 130 to 112 oz. To understand these changes, a dynamic model is developed of a resource constrained consumer optimally choosing the timing and quantity of discrete purchases, and piecewise continuous consumption paths of a perishable good. When calibrated to U.S. national average data, the model is found to be in close agreement, and rationalizes the observed drops in fresh produce and shopping frequency. A household fixed effects model confirms that shopping frequency and fresh produce consumption are causally linked. Of food retail environmental factors tested using a household level random effects model, the presence of supercenters and club stores have the largest impact on shopping frequency and fresh produce consumption. Impacts are decomposed into direct effects and effects mediated through shopping frequency. Nutritive aspects of food perishability are discussed and it is hypothesized that shopping frequency and many diet-based diseases are interrelated as households optimally manage their food inventory.