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.
‘Eating raw fruits and vegetables such as kiwis, bananas, apples, dark leafy greens, cucumber, carrots, citrus fruits and fresh berries may lower depression symptoms and improve mental health, more than cooked, canned and processed food.’
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.