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Eating raw fruits and vegetables could be a simple answer to feeling better mentally.
University of Otago researchers have discovered that the fresher fruits and vegetables are, the better a person's mental health and wellbeing is.
Psychology senior lecturer and lead author of the study Dr Tamlin Conner says public health campaigns have historically focused on aspects of quantity for the consumption of fruit and vegetables, such as 5+ a day.
''We used to think about what we ate in relation to our physical health, but now there is more evidence suggesting it also impacts on how we feel.''
The study, published in Frontiers in Psychology, found that for mental health, in particular, it may also be important to consider the way in which produce is 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.
It is thought the cooking and processing of fruits and vegetables has the potential to diminish nutrient levels, which likely limits the delivery of nutrients that are essential for mental health.
''It matters the way we eat. Small lifestyle changes can make a difference, but they're not easy to do.''
For the study, more than 400 young adults aged 18 to 25 from New Zealand and the United States 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 variables, raw fruit and vegetable consumption predicted lower levels of mental illness symptomatology, such as depression, and improved levels of psychological well-being including positive mood, life satisfaction and flourishing. These mental health benefits were significantly reduced for cooked, canned and/or processed fruits and vegetables.
The results suggest policies, promotions and interventions designed to increase raw fruit and vegetable consumption may provide a way to improve mental health in the young adult population, who remain vulnerable to developing mental disorders, she says.
As it was only a correlational study, the team had now moved on to a randomised control study using the food that scored the highest in the earlier study - kiwifruit.
Study participants with very low vitamin C levels from not eating many fruit and vegetables are being asked to eat two kiwifruit a day over a month to see if it affects their mental health and wellbeing.
''If we show a casual relationship between eating fresh fruit and vegetables and mental health we will be in a better position to make policy recommendations.''
As well as influencing government policy, Dr Conner hoped it could also influence individuals food choices.
''If eating that banana makes you less grumpy when you go home at night, then it's useful information.''