This paper investigates to what extent behavioural traits, such as patience, risk aversion and self-control are trainable. If they are, this would open new prospects to improve lifestyle choices and health. We conduct a randomised field experiment with 139 subjects to investigate the effects of a psychological training intervention – consisting of mindfulness training – affects patience, risk aversion and self-control. We also measure the effects of the intervention on a range of health-related behaviours. We do not find strong evidence that mindfulness training changes decision-making processes. We find evidence that it reduces reported levels of stress, but the effects on health-related behaviours are mixed.