The current study examines the impact of a nutrition rating system on consumers’ food purchases in supermarkets.

Aggregate sales data for 102 categories of food (over 60 000 brands) on a weekly basis for 2005–2007 from a supermarket chain of over 150 stores are analysed. Change in weekly sales of nutritious and less nutritious foods, after the introduction of a nutrition rating system on store shelves, is calculated, controlling for seasonality and time trends in sales.

One hundred and sixty-eight supermarket stores in the north-east USA, from January 2005 to December 2007.

Consumers purchasing goods at the supermarket chain during the study period.

After the introduction of the nutrition ratings, overall weekly food sales declined by an average of 3637 units per category (95 % CI –5961, –1313; P<0·01). Sales of less nutritious foods fell by 8·31 % (95 % CI –13·50, –2·80 %; P=0·004), while sales of nutritious foods did not change significantly (P=0·21); as a result, the percentage of food purchases rated as nutritious rose by 1·39 % (95 % CI 0·58, 2·20 %; P<0·01). The decrease in sales of less nutritious foods was greatest in the categories of canned meat and fish, soda pop, bakery and canned vegetables.

The introduction of the nutrition ratings led shoppers to buy a more nutritious mix of products. Interestingly, it did so by reducing purchases of less nutritious foods rather than by increasing purchases of nutritious foods. In evaluating nutrition information systems, researchers should focus on the entire market basket, not just sales of nutritious foods.