While their physical health benefits are widely known, research linked a regular diet of fruits and vegetables to happiness, higher life satisfaction, and better mental health. But what about the way you consume them? Does it make a difference whether you eat your produce in cooked, raw, canned or processed form?

Researchers from the University of Otago in New Zealand decided to find out and the results point to a clear winner. The study titled "Intake of Raw Fruits and Vegetables Is Associated With Better Mental Health Than Intake of Processed Fruits and Vegetables" was published in the journal Frontiers in Psychology on April 10.

"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," said study author Dr. Tamlin Conner, a senior lecturer of psychology at the university. She conducted the study along with psychology Ph.D. student Kate Brookie and postgraduate honors student Georgia Best.

For a cross-sectional survey, 422 young adults (ranging from 18 to 25 years of age) living in New Zealand and the United States were assessed. This age group was chosen since they are associated with the lowest intake of fruits and vegetables of all age groups, but are also at high risk of mental health problems.

The participants were predominantly female (66%) and white (67%). They were asked to complete an online survey to reveal their eating habits, lifestyle and mental health. The researchers also collected data on demographic variables such as sleep, exercise, socioeconomic status, gender, ethnicity etc.

Even when controlling for demographic and health covariates, a significant association was observed between raw fruits and vegetables and better mental health outcomes when compared to cooked or canned (processed) fruits and vegetables. Even though cooking can offer benefits such as making food easier to chew and increasing antioxidants, Conner suggested that cooking, canning or processing certain produce may have a negative impact on the nutrient levels.

"This likely limits the delivery of nutrients that are essential for optimal emotional functioning," she explained. "This research is increasingly vital as lifestyle approaches such as dietary change may provide an accessible, safe, and adjuvant approach to improving mental health."

Previous studies noted that cooking vegetables can diminish vitamin C and vitamin B levels, as well as destroy beneficial enzymes. The length of cooking time should also be considered as longer cooking time appears to be linked to a greater loss of water-soluble vitamins. 

The researchers noted that raw consumption predicted lower levels of mental disorders such as depression and improved levels of psychological well-being. This included a positive mood and life satisfaction. According to the study, the top ten raw foods linked to better mental health were carrots, bananas, apples, dark leafy greens like spinach, grapefruit, lettuce, citrus fruits, fresh berries, cucumber, and kiwifruit.