Researchers at Melbourne's Deakin University have found its protective powers stem from an ability to regulate the brain's natural level of zinc, which can prove toxic at elevated levels.

Cellular biologist and project leader Professor Leigh Ackland said previous research had shown a reduced incidence of neurodegenerative diseases in populations with a diet rich omega-3 fatty acids.

"We found that when the level of DHA in neuronal cells drops, the level of zinc rises," she said.

"The higher levels of zinc can be toxic, resulting in cell death ... a key feature of neurodegenerative diseases, including Alzheimer's.

"We believe that having omega-3 fatty acids in the diet helps keep the levels of zinc in the brain in balance and helps prevents the increase in levels that triggers cell death."