A lifelong diet that is rich in omega-3 fatty acids - found in fish oils - can decrease growth of breast cancer tumours by 30 percent, a new research has revealed.

Study authors David Ma, a professor in Guelph`s Department of Human Health and Nutritional Sciences, said that their study shows that lifelong exposure to omega-3s had a beneficial role in disease prevention - in this case, breast cancer prevention.

Ma said that health advocates have long believed that diet may significantly help in preventing cancer but epidemiological and experimental studies to back up such claims have been lacking, and human studies have been inconsistent.

For their research, they created a novel transgenic mouse that produced both omega-3 fatty acids and develops aggressive mammary tumours. The team compared those animals to mice genetically engineered only to develop the same tumours.

Mice producing omega-3s developed only two-thirds as many tumours - and tumours were also 30-per-cent smaller - as compared to the control mice.

"The difference can be solely attributed to the presence of omega-3s in the transgenic mice - that`s significant," Ma said.

"The fact that a food nutrient can have a significant effect on tumour development and growth is remarkable and has considerable implications in breast cancer prevention," he added.

The study has been published in the Journal of Nutritional Biochemistry.