Abstract Purpose - To evaluate an online ‘teachable moment’ intervention to promote healthy eating for overweight and food intolerance symptoms. Design/methodology/approach – The study involves a 2 x 2 factorial design with two conditions: group (weight loss vs food intolerance) and condition (intervention vs control). The intervention aimed to generate a ‘teachable moment’ by providing knowledge regarding the relationship between food and the problem (overweight or food intolerance), focusing on the negative aspects of the problem, creating a behavioural model, and encouraging hope and reinvention. Participants receiving the intervention (n = 22) completed measures of dietary behaviour and either weight or food intolerance symptoms before receiving the intervention and again one month later. Control participants (n = 20) provided measures but did not receive the intervention. Findings - There were no significant reductions in weight or food intolerance symptoms. However, compared to control participants, participants in the intervention conditions reported greater intentions to eat healthily (p = .01) and improved healthy eating behaviour over time, following both an intention-to-treat (p = .046) and explanatory analysis (p = .042). Practical implications - Encouraging individuals to perceive their everyday situation as a time for change and adopt healthier behaviour early on, may prevent future diet-related medical events. This has benefits for both the individual and for health care costs. Originality/value - A quick and easy to administer online ‘teachable moment’ intervention improves dietary behaviour and can be minimally adapted to suit individuals with differing health needs.