The Mediterranean diet can provide significant help to those suffering from severe depression, Australian researchers have discovered.

Mediterranean diet has long been known to have significant physical health benefits. Now researchers from Melbourne's Deakin University have discovered that it can also help those suffering mental health issues.

The team from Deakin put dozens of patients with major depressive disorders on a Mediterranean-style diet rich in protein, legumes, fresh fruit and vegetables, olive oil and nuts.

After 12 weeks of health eating, researchers said that one third of the participants reported a significant improvement in their mood and symptoms.

Felice Jacka, director of Deakin University's Food and Mood Center, said the Mediterranean diet had previously been credited with improving cardiovascular health, reducing the risk of diabetes and increasing longevity.

"We already know that diet has a very potent impact on the biological aspects of our body that affect depression risks," Jacka told the Australian Broadcasting Corporation (ABC) on Tuesday.

"The immune system, brain plasticity, and gut microbiota seem to be central not just to our physical health, but also our mental health.

"And diet, of course, is the main factor that affects the gut microbiota."

Jacka randomly selected the participants to embrace the Mediterranean diet and reduce their intake of sweets, refined cereals, fried foods and sugary drinks.

Another group of participants received social support with only eight percent of those in the social support group showing improvements in their symptoms.

Sarah Keeble, a participant in the diet-switch, described the program as life changing.

"I felt clearer in my mind. I felt balanced. I felt happier. I actually had a lot more energy. I felt I could really kick this in the butt," she said.

"It's not going to cure depression, but you can certainly handle it very well.

Keeble said she had continued the diet after finishing the program and is now doing a diploma in health science.

"I got so motivated because I felt so much better, better than I had in so long," Keeble told the ABC.

"I'd like to help people in this situation where they think there's no hope."