Daily diet that includes over 30 per cent ultra-processed food is associated with a significant risk of depression, according to a study.

Ultra-processed foods are not limited to typical junk and fast foods. They also include mass-produced and highly refined products like diet soft drinks, some fruit juices and flavoured yoghurts, margarine, packet preparations of foods like scrambled egg and mashed potato and many ready-to-heat-and-eat dishes.

The new finding, recently published in the Journal of Affective Disorders, provides further evidence of the wide-ranging harms of diets loaded with cheap, well-marketed but often nutrient poor convenience foods.

The researchers from Deakin University and Cancer Council Victoria looked at associations between ultra-processed food consumption and depression in over 23,000 Australians from the Melbourne Collaborative Cohort Study.

"While Australians eat a lot of ultra-processed foods, the link with depression has never been assessed in a group of Australians until now," said Melissa Lane, who completed the research as part of her Ph.D. Studies at Deakin University's Food and Mood Center.

"Australians who ate the most ultra-processed food had about a 23 per cent higher risk of depression compared to those who ate the least amount," Lane said in a statement.

The study comprised people who were initially not taking any medication for depression and anxiety and were followed for over 15 years.

Even after accounting for factors like smoking and lower education, income and physical activity, which are linked to poor health outcomes, the findings show greater consumption of ultra-processed food is associated with a higher risk of depression.        Lane said that while the study was not proof the ultra-processed food necessarily caused depression, it showed that eating more ultra-processed food was associated with an increased risk of depression.

"Depression is one of the most common mental disorders across the globe and it is a major health problem because it negatively affects daily living and well-being through lasting low energy, changes in appetite and sleep, loss of interest or pleasure, sadness, and sometimes thoughts of suicide," Lane said.

"Identifying a critical level of consumption that may increase the risk of depression will help consumers, healthcare professionals and policymakers make more informed decisions around dietary choices, interventions and public health strategies," the researcher added.