Seeking the feel good factor? Go natural.

That is the simple message from University of Otago researchers who have discovered raw fruit and vegetables may be better for your mental health than cooked, canned and processed fruit and vegetables.

Dr Tamlin Conner, Psychology Senior Lecturer and lead author, 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 study, just published in Frontiers in Psychology, found that for mental health in particular, it may also be important to consider the way in which produce was prepared and consumed.

"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," she says.

Dr Conner believes this could be because the cooking and processing of fruit and vegetables has the potential to diminish nutrient levels.

"This likely limits the delivery of nutrients that are essential for optimal emotional functioning."

For the study, more than 400 young adults from New Zealand and the United States aged 18 to 25 were surveyed. This age group was chosen as young adults typically have the lowest fruit and vegetable consumption of all age groups and are at high risk for mental health disorders.

The group's typical consumption of raw versus cooked and processed fruits and vegetables were assessed, alongside their negative and positive mental health, and lifestyle and demographic variables that could affect the association between fruit and vegetable intake and mental health (such as exercise, sleep, unhealthy diet, chronic health conditions, socioeconomic status, ethnicity, and gender).

"Controlling for the covariates, raw fruit and vegetable consumption predicted lower levels of mental illness symptomology, such as depression, and improved levels of psychological wellbeing including positive mood, life satisfaction and flourishing. These mental health benefits were significantly reduced for cooked, canned, and processed fruits and vegetables.

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

* The top 10 raw foods related to better mental health were: carrots, bananas, apples, dark leafy greens such as spinach, grapefruit, lettuce, citrus fruits, fresh berries, cucumber, and kiwifruit.