We examine the effect of supercenter market share on consumers’ food-at-home purchasing habits in the United States. We measure healthfulness several different ways to ensure robustness, but all measurements place a greater value on fresh fruits and vegetables and whole grains than on processed foods high in sugar and sodium. We find that from 1998–2006 consumers generally purchased less healthful foods at supercenters than they do at supermarkets. Moreover, a one-percent increase in the local market share of supercenters results in a decrease in purchase healthfulness for groceries of 0.10 to 0.46 percent. This relationship is statistically significant and robust.