Strengths and limitations
inability to recall food
Strengths in this study include the RCT protocol, use of 3-day 24-hour dietary recalls by unannounced phone calls using the USDA five-step multiple-pass method, and a relatively long intervention of 4 months, even up to the study midpoint. Additionally, the use of store loyalty cards as a means to electronically implement the discount intervention at the point-of-purchase is a novelty.Limitations include the disruption of the study by the nationwide lockdown due to the COVID-19 pandemic, which extended the length of time between visits for many participants. However, the extended time periods did not have a significant effect on the study outcomes. Some participants did not adhere to the 100% shopping requirement at Foodtown markets. However, the percentage of total shopping at the designated supermarket also did not affect the outcome measures. Another limitation of this study may be the use of caloric density as a criteria for the discount intervention rather than the degree of food processing (not processed, minimally processed, or ultra-processed); however many dietary intervention studies use caloric density given its strong correlation with caloric intake, the main factor associated with weight change. Also, the use of self-reported measurements of dietary intake is subject to errors brought on by inaccurate reporting of food amounts and inability to recall food and drinks consumed. Finally, the large number of inclusion/exclusive eligibility criteria may limit generalizability.In summary, the results of this study indicate that discounts, especially at the 30% level, can translate into increased intake of vegetables and diet soda. The findings show that economic incentives can promote healthful intake. Thus, reducing the price of low-ED foods, especially vegetables, can be a useful strategy for public health officials and policymakers to consider for improving access to healthful foods and beverages and promoting healthy dietary intake behaviors.