A new study has found that eating raw fruit and vegetables such as kiwis, bananas, apples and dark leafy greens may lower symptoms of depression and improve mental health, more than cooked, canned and processed food.

Consuming raw fruits and vegetables leads to lower levels of mental illness symptomology, such as depression, as per the findings. It also improved levels of psychological well-being including a positive mood and life satisfaction.

Lead author Tamlin Conner, senior lecturer at the University of Otago in Dunedin, New Zealand said, "Our research has highlighted that the consumption of fruit and vegetables in their 'unmodified' state is more strongly associated with better mental health compared to cooked/canned/processed fruit and vegetables."

Conner said, when the fruits and vegetables are cooked, canned and processed, they lose their mental health benefits as the process potentially diminishes the nutrient levels.

"Cooking and processing likely limits the delivery of nutrients that are essential for optimal emotional functioning," Conner added.

For the study more than 400 young adults from New Zealand and the US aged 18 to 25 years were surveyed.

Conner says public health campaigns have historically focused on aspects of quantity for the consumption of fruit and vegetables (such as 5+ a day).

However, the new study found that for mental health in particular, it may also be important to consider the way in which produce was prepared and consumed.

"This research is increasingly vital as lifestyle approaches such as dietary change may provide an accessible, safe and adjuvant approach to improving mental health," Conner said.

The study was published in the journal Frontiers in Psychology.