There are surprisingly few randomised, controlled trials into the effects of dietary change on mood and cognition in healthy individuals. Here we examined the effects of 10 days of changing to a nutrient-rich diet on mood and cognitive performance. Young female adults (N=25) were randomised to a diet change (DC), or a no change (NC) control group. Those in the DC condition adhered to the nutrient-dense Mediterranean diet. Mood and cognitive performance were assessed at baseline and on day 10. Compared with the NC group, the DC group showed significant improvements in self-rated vigour, alertness and contentment. Changes in cognitive tasks were somewhat inconsistent. These preliminary findings require verification in larger trials but suggest that appropriate dietary change may benefit mood and some aspects of cognitive performance in healthy adults.