Use of financial incentives and text message feedback to increase healthy food purchases in a grocery store cash back program: a randomized controlled trial

BACKGROUND: The HealthyFood (HF) program offers members up to 25% cash back monthly on healthy food purchases. In this randomized controlled trial, we tested the efficacy of financial incentives combined with text messages in increasing healthy food purchases among HF members. METHODS: Members receiving the lowest (10%) cash back level were randomized to one of six arms: Arm 1 (Usual Care): 10% cash back, no weekly text, standard monthly text; Arm 2: 10% cash back, generic weekly text, standard monthly text; Arm 3: 10% cash back, personalized weekly text, standard monthly text; Arm 4: 25% cash back, personalized weekly text, standard monthly text; Arm 5: 10 + 15%NET cash back, personalized weekly text, standard monthly text; and, Arm 6: 10 + 15%NET cash back, personalized weekly text, unbundled monthly text. In the 10 + 15%NET cash back, the cash back amount was the baseline 10% plus 15% of the net difference between healthy and unhealthy spending. The generic text included information on HF and healthy eating, while the personalized text had individualized feedback on purchases. The standard monthly text contained the cash back amount. The unbundled monthly text included the amount lost due to unhealthy purchases. The primary outcome was the average monthly percent healthy food spending. Secondary outcomes were the percent unhealthy food spending, and the percent healthy and unhealthy food items. RESULTS: Of the members contacted, 20 opted out, and 2841 met all inclusion criteria. There were no between-arm differences in the examined outcomes. The largest mean (standard deviation) difference in percent healthy spending was between Arm 1 (24.8% [11%]) and Arm 2 (26.8% [13%]), and the largest mean difference in percent unhealthy spending was also between Arm 1 (24.4% [20%]) and Arm 2 (21.7% [17%]), but no differences were statistically significant after correction for multiple comparisons. CONCLUSIONS: None of the tested financial incentive structures or text strategies differentially affected food purchasing. Notably, more than doubling the cash back amount and introducing a financial disincentive for unhealthy purchases did not affect purchasing. These findings speak to the difficulty of changing shopping habits and to the need for innovative strategies to shift complex health behaviors. TRIAL REGISTRATION: NCT02486588 Increasing Engagement with a Healthy Food Benefit. The trial was prospectively registered on July 1, 2015. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12889-019-6936-5) contains supplementary material, which is available to authorized users.