The effects of a 25% discount on fruits and vegetables: results of a randomized trial in a three-dimensional web-based supermarket

Wilma E Waterlander, Ingrid H M Steenhuis, Michiel R de Boer, Albertine J Schuit, Jacob C Seidell, Wilma E Waterlander, Ingrid H M Steenhuis, Michiel R de Boer, Albertine J Schuit, Jacob C Seidell

Abstract

Background: Lowering the price of fruit and vegetables is a promising strategy in stimulating the purchase of those foods. However, the true effects of this strategy are not well studied and it is unclear how the money saved is spent. The aim of this study is to examine the effects of a 25% discount on fruits and vegetables on food purchases in a supermarket environment.

Methods: A randomized controlled trial with two research conditions was conducted: a control condition with regular prices (n = 52) and an experimental condition with a 25% discount on fruits and vegetables (n = 63). The experiment was carried out using a three-dimensional web-based supermarket, which is a software application in the image of a real supermarket. Data were collected in 2010 in the Netherlands. Participants received a fixed budget and were asked to buy weekly household groceries at the web-based supermarket. Differences in fruit and vegetable purchases, differences in expenditures in other food categories and differences in total calories were analyzed using independent samples t-tests and multiple linear regression models accounting for potential effect modifiers and confounders.

Results: The purchased amount of fruit plus vegetables was significantly higher in the experimental condition compared to the control condition (Δ984 g per household per week, p = .03) after appropriate adjustments. This corresponds to a 25% difference compared to the control group. Both groups had similar expenditures in unhealthier food categories, including desserts, soda, crisps, candy and chocolate. Furthermore, both groups purchased an equal number of food items and an equal amount of calories, indicating that participants in the discount condition did not spend the money they saved from the discounts on other foods than fruits and vegetables.

Conclusion: A 25% discount on fruits and vegetables was effective in stimulating purchases of those products and did neither lead to higher expenditures in unhealthier food categories nor to higher total calories purchased. Future studies in real supermarkets need to confirm these findings.

Figures

Figure 1
Figure 1
Impression of the three-dimensional web-based supermarket.
Figure 2
Figure 2
CONSORT Statement Flow Diagram.

References

    1. Swinburn B, Egger G, Raza F. Dissecting obesogenic environments: the development and application of a framework for identifying and prioritizing environmental interventions for obesity. Prev Med. 1999;29(6):563–570. doi: 10.1006/pmed.1999.0585.
    1. Kim D, Kawachi I. Food taxation and pricing strategies to "thin out" the obesity epidemic. Am J Prev Med. 2006;30(5):430–437. doi: 10.1016/j.amepre.2005.12.007.
    1. Brownell KD, Farley T, Willett WC, Popkin BM, Chaloupka FJ, Thompson JW, Ludwig DS. The public health and economic benefits of taxing sugar-sweetened beverages. N Engl J Med. 2009;361(16):1599–1605. doi: 10.1056/NEJMhpr0905723.
    1. Kuchler F, Tegene A, Harris M. Taxing snack foods: what to expect for diet and tax revenues. Agri Inf Bull. 2004;08(747):1–12.
    1. Giesen JC, Payne CR, Havermans RC, Jansen A. Exploring how calorie information and taxes on high-calorie foods influence lunch decisions. The Am J Clin Nutr. 2011. doi:10.3945/ajcn.110.008193.
    1. Cash SB, Sunding DL, Zilberman D. Fat taxes and thin subsidies: prices, diet, and health outcomes. Acta Agriculture Scand Section C. 2005;2:167–174.
    1. Kuchler F, Tegene A, Harris M. Taxing snack foods: manipulating diet quality or financing information programs. Rev Agric Econ. 2005;27(1):4–20. doi: 10.1111/j.1467-9353.2004.00204.x.
    1. Powell LM, Chaloupka FJ. Food prices and obesity: evidence and policy implications for taxes and subsidies. Milbank Q. 2009;87(1):229–257. doi: 10.1111/j.1468-0009.2009.00554.x.
    1. Waterlander WE, Steenhuis IH, de Vet E, Schuit AJ, Seidell JC. Expert views on most suitable monetary incentives on food to stimulate healthy eating. Eur J Publ Health. 2010;20(3):325–331. doi: 10.1093/eurpub/ckp198.
    1. Waterlander WE, de Mul A, Schuit AJ, Seidell JC, Steenhuis IHM. Perceptions on the use of pricing strategies to stimulate healthy eating among residents of deprived neighbourhoods: a focus group study. Int J Behav Nutr Phys Act. 2010;7(44):doi:10.1186/1479–5868-1187-1144.
    1. Steenhuis IH, Waterlander WE, de Mul A. Consumer food choices: the role of price and pricing strategies. Publ Health Nutrition. 2011;14:2220–2226. doi: 10.1017/S1368980011001637.
    1. Herman DR, Harrison GG, Jenks E. Choices made by low-income women provided with an economic supplement for fresh fruit and vegetable purchase. J Am Diet Assoc. 2006;106(5):740–744. doi: 10.1016/j.jada.2006.02.004.
    1. Veblen T. The preconceptions of economic science. Q J Econ. 1900;14(2):240–269. doi: 10.2307/1883770.
    1. Wall J, Ni Mhurchu C, Blakely T, Rodgers A, Wilton J. Effectiveness of monetary incentives in modifying dietary behavior:a review of randomized, controlled trials. Nutr Rev. 2006;64(12):518–531. doi: 10.1111/j.1753-4887.2006.tb00185.x.
    1. French SA, Story M, Jeffery RW, Snyder P, Eisenberg M, Sidebottom A, Murray D. Pricing strategy to promote fruit and vegetable purchase in high school cafeterias. J Am Diet Assoc. 1997;97(9):1008–1010. doi: 10.1016/S0002-8223(97)00242-3.
    1. French SA. Pricing effects on food choices. J Nutr. 2003;133(3):841S–843S.
    1. Ni Mhurchu C, Blakely T, Jiang Y, Eyles HC, Rodgers A. Effects of price discounts and tailored nutrition education on supermarket purchases: a randomized controlled trial. Am J Clin Nutr. 2010;91(3):736–747. doi: 10.3945/ajcn.2009.28742.
    1. Ni Mhurchu C. Food costs and healthful diets: the need for solution-oriented research and policies. Am J Clin Nutr. 2010;92:1007–1008. doi: 10.3945/ajcn.110.002717.
    1. Andreyeva T, Long MW, Brownell KD. The impact of food prices on consumption: a systematic review of research on the price elasticity of demand for food. Am J Public Health. 2010;100(2):216–222. doi: 10.2105/AJPH.2008.151415.
    1. Lock K, Pomerleau J, Causer L, Altmann DR, McKee M. The global burden of disease attributable to low consumption of fruit and vegetables: implications for the global strategy on diet. Bull World Health Organ. 2005;83(2):100–108.
    1. Waterlander WE, Scarpa M, Lentz D, Steenhuis IH. The virtual supermarket: an innovative research tool to study consumer food purchasing behaviour. BMC Publ Health. 2011;11(1):589. doi: 10.1186/1471-2458-11-589.
    1. Groceries (boodschappen)
    1. Roodenburg AJC, Popkin BM, Seidell JC. Development of international criteria for a front of package food labelling system: the international Choices Programme. Eur J Clin Nutr. 2011;65:1190–1200. doi: 10.1038/ejcn.2011.101.
    1. Epstein LH, Dearing KK, Roba LG, Finkelstein E. The influence of taxes and subsidies on energy purchased in an experimental purchasing study. Psychol Sci. 2010;21:406–414. doi: 10.1177/0956797610361446.
    1. Nederkoorn C, Havermans RC, Giesen JC, Jansen A. High tax on high energy dense foods and its effects on the purchase of calories in a supermarket: an experiment. Appetite. 2011;56(3):760–765. doi: 10.1016/j.appet.2011.03.002.
    1. Hulshof KFAM, Ocke MC, van Rossum CTM, Burma-Rethans EJM, Brants HAM, Drijvers JJMM, Doest D. RIVM-report nr 350030002; TNO report nr V6000. Bilthoven: National Institute for Public Health and the Environment (RIVM); 2003. Results of the food consumption survey 2003 (Resultaten van de voedselconsumptiepeiling 2003)
    1. Lichtenstein DR, Ridgway NM, Netemeyer RG. Price perceptions and consumer shopping behavior: a field study. J Mark Res. 1993;30:234–245. doi: 10.2307/3172830.
    1. Verplanken B, Orbell S. Reflections on past behavior: a self-report index of habit strength. JASP. 2003;33(6):1313–1330.
    1. Giesen JCAH, Havermans RC, Nederkoorn C, Jansen A. Impulsivity in the supermarket: Responses to calorie taxes and subsidies in healthy weight undergraduates. Appetite. 2011. doi:10.1016/j.appet.2011.09.026.
    1. Standard Income (Modaal inkomen)
    1. Monsivais P, Aggarwal A, Drewnowski A. Are socio-economic disparities in diet quality explained by diet cost? J Epidemiol Community Health. 2010. doi:10.1136/jech.2010.122333.
    1. Drewnowski A, Darmon N. Food choices and diet costs: an economic analysis. J Nutr. 2005;135(4):900–904.
    1. Waterlander WE, de Haas WE, van Amstel I, Schuit AJ, Twisk JW, Visser M, Seidell JC, Steenhuis IH. Energy density, energy costs and income - how are they related? Publ Health Nutrition. 2010;13(10):1599–1608. doi: 10.1017/S1368980009992989.
    1. Drewnowski A. The cost of US foods as related to their nutritive value. Am J Clin Nutr. 2010;92(5):1181–1188. doi: 10.3945/ajcn.2010.29300.
    1. Ludwig DS, Nestle M. Can the food industry play a constructive role in the obesity epidemic? JAMA. 2008;300(15):1808–1811. doi: 10.1001/jama.300.15.1808.
    1. Nestle M. In: Food politics How the food industry influences nutrition and health. Goldstein E, editor. Berkeley: University of California Press; 2007. Conclusion. The politics of food choice; pp. 358–374.
    1. Cassady D, Jetter KM, Culp J. Is price a barrier to eating more fruit and vegetables for low-income families? J Am Diet Assoc. 2007;107:1909–1915. doi: 10.1016/j.jada.2007.08.015.
    1. European Commission. Risk Issues. Special Eurobaromater 238/Wave 64.1. 2006.
    1. Wiig K, Smith C. The art of grocery shopping on a food stamp budget: factors influencing the food choices of low-income women as they try to make ends meet. Publ Health Nutrition. 2009;12(10):1726–1734. doi: 10.1017/S1368980008004102.
    1. Han S, Gupta S, Lechmann DR. Consumer price sensitivity and price thresholds. J Retail. 2001;77:435–456. doi: 10.1016/S0022-4359(01)00057-4.
    1. Jensen JD, Smed S. Cost-effective design of economic instruments in nutrition policy. Int J Behav Nutr Phys Act. 2007;4:10. doi: 10.1186/1479-5868-4-10.
    1. Vanhuelle M, Laurent G, Dreze X. Consumers' immediate memory for prices. J Consum Res. 2006;33:163–171. doi: 10.1086/506297.
    1. Anderson ET, Simester DI. The role of sale signs. Mark Sci. 1998;17(2):139–155. doi: 10.1287/mksc.17.2.139.
    1. Blattberg RC, Briesch R, Fox EJ. How promotions work. Mark Sci. 1995;14(3):G122–G132. doi: 10.1287/mksc.14.3.G122.
    1. van Rossum CT, Fransen HP, Verkaik-Kloosterman H, Buurma-Rethans EJM, Ocke MC. Dutch National Food Consumption Survey 2007-2010. Bilthoven: National Institute for Public Health and the Environment (RIVM); 2011.
    1. Scarborough P, Nnoaham KE, Clarke D, Capewell S, Rayner M. Modelling the impact of a healthy diet on cardiovascular disease and cancer mortality. J Epidemiol Community Health. 2010. doi:10.1136/jech.2010.114520.
    1. Naska A, Fouskakis D, Oikonomou E, Almeida MD, Berg MA, Gedrich K, Moreiras O, Nelson M, Trygg K, Turrini A. et al.Dietary patterns and their socio-demographic determinants in 10 European countries: data from the DAFNE databank. Eur J Clin Nutr. 2006;60(2):181–190. doi: 10.1038/sj.ejcn.1602284.
    1. CDC. Morbidity and Mortality Weekly Report. Vol. 59. CDC. Center for Disease Control and Prevention; 2010. State-Specific trends in fruit and vegetable consumption among adults -- United States, 2000-2009.
    1. Spending and market share supermarkets.
    1. Sharpe KM, Staelin R, Huber J. Using extremeness aversion to fight obesity: policy implications of contaxt dependent demand. J Consum Res. 2008;35:406–422. doi: 10.1086/587631.
    1. Perloff JM. Microeconomic. 4. Boston: Pearson Education; 2007.

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