The Grocery Purchase Quality Index: A unique Approach to Measure Diet Quality from Purchase Patterns

December 18, 2019
Retail Industry Insights

By Elizabeth Hall, MS, RDN, LDN, Corporate/Retail RD for K-VA-T Food Stores Inc.

Despite health benefits associated with adequate nutrition, many Americans consume a diet of poor nutrient quality,1-2 which is often reflected in their purchase patterns.3 Supermarket promotions that prioritize health can provide fertile ground to improve the healthfulness of purchases and foster business growth.4-7 While sales lift of products in these health-related promotions show promising results,4 whether or not these programs alter consumer diet quality is unknown. This is mostly due to diet quality being traditionally determined from intake data, which is difficult to measure and often inaccurate if self-reported. A scale that determines diet quality from consumer purchase patterns allows for more accurate, readily available information that can be used to measure return on investment and public health significance of health-related programming in the supermarket environment.

The Grocery Purchase Quality Index-2016 (GPQI-2016) is a new validated measurement tool that uses the United States Department of Agriculture (USDA) Food Plans as the basis for assessing the quality of grocery purchases in a household.8 The most recent USDA Food Plans were released in 2007 by the USDA Center for Nutrition Policy and Promotion (USDA-CNPP) with each plan representing a “model market basket.”9-10 The four plans also correspond to varying income levels or the amount of disposable income spent on food to be consumed at home 9-10 and incorporate nutrition recommendations from the 2005 Dietary Guidelines for Americans,11 the USDA Food Patterns,12 and the Dietary Reference Intakes.13 Using the USDA Food Plans as a guide, the GPQI-2016 provides defined target values for each food category in order to show the level at which a consumer’s purchases meet diet recommendations.8 

The overall GPQI score provides a comparable estimate to the Healthy Eating Index (HEI), another validated tool to measure diet quality.14 The most recent HEI is based on the 2015-2020 USDA Dietary Guidelines15 and examines self-reported serving sizes of food consumed in order to assess overall nutrient intake and diet quality.16 As previously discussed, intake data by self-report is not as readily available or as accurate as purchase data in the form of transactions from a supermarket.14 Therefore, the GPQI-2016 offers promising results by analyzing purchase data as a more precise measure of diet quality for the home food environment,14 as well as an alternative outcome measure to evaluate the success of health-related programming in supermarket environments. 

References

1. Centers for Disease Control and Prevention. National Center for Chronic Disease Prevention and Health Promotion. Poor Nutrition. https://www.cdc.gov/chronicdisease/resources/publications/factsheets/nutrition.htm. Updated August 7, 2019. Accessed November 11, 2019.
2. U.S. Department of Health and Human Services, U.S. Department of Agriculture. 2015-2020 Dietary Guidelines for Americans 2015-2020: Current Eating Patterns in the United States. https://health.gov/dietaryguidelines/2015/guidelines/chapter-2/current-eating-patterns-in-the-united-states/. Published December 2015. Accessed September 29, 2019.
3. U.S. Department of Agriculture, Economic Research Service, Volpe, R, Okrent A. Economic Information Bulletin (EIB-102): Assessing the Healthfulness of Consumers’ Grocery Purchases. https://www.ers.usda.gov/webdocs/publications/43680/33405_eib102.pdf?v=0. Published November 2012. Accessed September 29, 2019.
4. Gittelsohn J, Rowan M, Gadhoke P. Interventions in small food stores to change the food environment, improve diet, and reduce risk of chronic disease. Prev Chronic Dis. 2012;9:110015. 
5. Baic S, Thompson JL. Prevent it: Using grocery store tours as an educational tool to promote heart health. ACSMs Health Fit J. 2007;11:15-20.
6. Carson JAS, Hedl JJ. Smart shoppers tours: outcome evaluation. J Nutr Educ. 1998;30:323-331.
7. Smith SC, Kalina L. Evaluation of the Kids’ Shop Smart! Tour. Can J Diet Pract Res.
   2004;65:10-14.
8. Brewster PJ, Guenther PM, Jordan KC, Hurdle JF. The Grocery Purchase Quality Index-2016: An innovative approach to assessing grocery food purchases. J Food Compos Anal. 2017;64:119-126.
9. Carlson A, Lino M, Fungwe TV. The Low-Cost, Moderate-Cost, and Liberal Food Plans, 2007, CNPP-20. United States Department of Agriculture, Center for Nutrition Policy and Promotion, Washington DC. 2007a.
10. Carlson A, Lino M, Juan W, Hanson K, Basiotis PP. Thrifty Food Plan, 2006, CNPP-19. United States Department of Agriculture, Center for Nutrition Policy and Promotion, Washington DC. 2007b.
11. 2005-2010 Dietary Guidelines for Americans: 7th edition. United States Department of Agriculture, United States Department of Health and Human Services, 2010. U.S. Government Printing Office, Washington DC.
12. Britten P, Marcoe K, Yamini S, Davis C, Development of food intake patterns for the MyPyramid Food Guidance System. J Nutr Educ Behav. 2006;38 (6):S78–92. 
13. Institute of Medicine. Dietary Reference Intakes: The Essential Guide to Nutrient Requirements. The National Academies Press, Washington, DC. 2006.
14. Brewster PJ, Durward CM, Hurdle JF, Stoddard GJ, Guenther PM. The Grocery Purchase Quality Index-2016 Performs Similarly to the Healthy Eating Index-2015 in a National Survey of Household Food Purchases. J Acad Nutr Diet. 2019;119(1):45-56.
15. 2015-2020 Dietary Guidelines for Americans: Eighth Edition. U.S. Department of Health and Human Services and U.S. Department of Agriculture Web site. http://health.gov/dietaryguidelines/2015/guidelines/. Published December 2015. Accessed November 9, 2016.
16. Krebs-Smith SM, Pannucci TE, Subar AF, et al. Update of the Healthy Eating Index: HEI-2015. J Acad Nutr Diet. 2018;118(9):1591-1602.