Background This study tested the efficacy of self‐affirmation in promoting fruit and vegetable consumption in a sample of participants comprising two groups at high risk of low consumption: young adults and mothers of school‐aged children with low social economic status (SES). Methods Baseline fruit and vegetable consumption was recorded for 85 participants (n = 26 mothers with low SES). Following randomisation to condition (Self‐Affirmed or Non‐Affirmed), participants viewed targeted, online, health recommendations about fruit and vegetable consumption. Fruit and vegetable intake was reported online every day for the following seven days. Results Self‐affirmed participants reported consuming significantly more portions of fruit and vegetables (SA M = 3.96, NA M = 2.81). Analyses of simple slopes indicated that the effect was greatest amongst lowest baseline consumers. Conclusions The findings demonstrate the efficacy of self‐affirmation in increasing fruit and vegetable consumption in individuals who are at risk of having a low intake and whose consumption put them at the greatest risk of negative health outcomes. Application of these findings could help to reduce health care costs, through the use of cost‐effective online interventions and reductions in treatment costs. Further research is needed to capitalise on the increased tailoring that online intervention allows in order to optimise the effects of self‐affirmation.