Immediate backfire? Nudging sustainable food choices and psychological reactance

•Using an online randomised controlled trial, we compared the effect of a purely reflective tool, the “think”, versus a hybrid nudge-think tool, the “nudge+”, on (N = 611) people’s willingness to choose environmentally sustainable food.•In the think condition, participants were encouraged to first reflect on a green pledge and then choose an appropriate nudge to comply with their pledge.•In the nudge+, condition, we altered the think by proposing a green default to participants who took the pledge.•We do not find any evidence of heterogeneous treatment effects by unconditional motivation levels of participants.•Nonetheless, we find nudging people, who are already motivated to eat sustainably in the short-term, after they have taken the pledge, leads to a backfire. This fades out when we control for people’s overall long-term motivations.