Exploring the impact of giving free food samples and loyalty cards on sustainable food choices: A stepped wedge trial in workplace food outlets

Free samples and loyalty cards are frequently used, but there is little rigorous empirical testing of their effects. We conducted a stepped wedge trial in 29 workplace food outlets to investigate their effects on sales of plant-based meals. Outlets were randomly assigned to three sequences that entered the intervention in the first, second, or third week of August 2022. Free samples of plant-based meals were given out in the first week of the intervention; loyalty cards were available throughout, entitling the bearer to a free meal after they had bought three. The intervention period ended in the last week of August for all outlets. The free meal could be redeemed until one month later. We did not find statistically significant effects of the interventions compared to the baseline period. Our process evaluation indicated that many participants preferred to eat their habitual meal or were unaware of the loyalty cards.