Leveraging delay discounting for health: Can time delays influence food choice?

Abstract

Delay discounting, the tendency to choose smaller immediate rewards over larger delayed rewards, is theorized to promote consumption of immediately rewarding but unhealthy foods at the expense of long-term weight maintenance and nutritional health. An untested implication of delay discounting models of decision-making is that selectively delaying access to less healthy foods may promote selection of healthier (immediately available) alternatives, even if they may be less desirable. The current study tested this hypothesis by measuring healthy versus regular vending machine snack purchasing before and during the implementation of a 25-s time delay on the delivery of regular snacks. Purchasing was also examined under a $0.25 discount on healthy snacks, a $0.25 tax on regular snacks, and the combination of both pricing interventions with the 25-s time delay. Across 32,019 vending sales from three separate vending locations, the 25-s time delay increased healthy snack purchasing from 40.1% to 42.5%, which was comparable to the impact of a $0.25 discount (43.0%). Combining the delay and the discount had a roughly additive effect (46.0%). However, the strongest effects were seen under the $0.25 tax on regular snacks (53.7%) and the combination of the delay and the tax (50.2%). Intervention effects varied substantially between vending locations. Importantly, time delays did not harm overall vending sales or revenue, which is relevant to the real-world feasibility of this intervention. More investigation is needed to better understand how the impact of time delays on food choice varies across populations, evaluate the effects of time delays on beverage vending choices, and extend this approach to food choices in contexts other than vending machines.

Trial registration: ClinicalTrials.gov, NCT02359916.

Keywords: Behavioral economics; Delay discounting; Food choice; Pricing interventions; Vending machines.

Figure 1

Data from dose-finding pilot study (N=170) of delay intervals. The line represents the proportion of healthy snacks chosen when increasingly long time delays were applied to regular snacks. Data are depicted with 4-neighbor smoothing. The number of instances where subjects exchanged their coupons for cash are shown just below the trendline. A 25-second delay interval was ultimately selected for the main trial.

Figure 2

Sequence of experimental conditions in the main trial. Conditions were implemented in the same order in all three vending locations. The duration of each condition was approximately 4 weeks.

Figure 3

Study outcomes by condition (means and standard error bars). Panel A depicts the proportion of total sales from healthy snacks as absolute percentages, with all healthy snack sales being significantly higher than under No Intervention in all other conditions. Panel B illustrates the lack of statistically significant differences in daily vending sales across conditions, whereas Panel C shows that daily vending revenue did not significantly vary by condition. Asterisks indicate significant difference from No Intervention at p<.001.

Figure 4

Changes in the proportion of sales from healthy snacks in the “blue collar” and “white collar” locations, expressed as a relative percentage of baseline sales (not an absolute percentage) under No Intervention in the respective location. Asterisk indicates a significant difference between locations at p<.05.