The importance of better understanding ways to improve mental health, and subjective well-being more generally, is an issue that is gaining increased prominence among public health professionals in the Western world. Cognitive behavioural therapy and pharmaceutical treatments are the primary interventions used currently by public health practitioners to improve mental health and well-being. While the role of diet in influencing physical health is now well-established, some recent research suggests that diet could also play a role in improving subjective well-being. A limitation with much of this existing research is its reliance on cross-sectional correlations, convenience samples and/or lack of adequate controls. In this study, we present evidence using the UK Household Longitudinal Survey (UKHLS) that subjective well-being responds in a dose-response fashion to increases in fruit and vegetable consumption. We take advantage of the longitudinal nature of the UKHLS by employing panel data analytical techniques (i.e. following the same individuals over time) and also controlling for time-variant confounders such as diet, health and lifestyle behaviours. Apart from being significant in a statistical sense, our estimates suggest that even modest increases in the consumption of fruit and vegetables could have comparable well-being effects to that of many big-hitting life events. Our findings, therefore, provide further evidence that persuading people to consume more fruits and vegetables may not only benefit their physical health in the long-run, but also their mental well-being in the short-run.