A key feature of this work is that the study was able to follow the same individuals over time. The study also controlled for alternative factors that may affect mental well-being, such as age, education, income, marital status, employment status, lifestyle and health, as well as consumption of other foods such as bread or dairy products.

The research showed a positive association between the quantity of fruit and vegetables consumed and people's self-reported mental well-being.

Specifically, the findings indicate that eating just one extra portion of fruits and vegetables a day could have an equivalent effect on mental well-being as around 8 extra days of walking a month (for at least 10 minutes at a time).

There appears to be accumulating evidence for the psychological benefits of fruits and vegetables. Despite this, the data show that the vast majority of people in the UK still consume less than their five-a-day.

Encouraging better dietary habits may not just be beneficial to physical health in the long run but may also improve mental well-being in the shorter term.