The omega-3 fats in fish should be chosen over flaxseed and other oils for the prevention of cancer, according to a study. University of Guelph Professor David Ma has discovered that marine-based omega-3s are eight times more effective at inhibiting tumour development and growth. 'This study is the first to compare the cancer-fighting potency of plant- versus marine-derived omega-3s on breast tumour development,' said the professor. 'There is evidence that both omega-3s from plants and marine sources are protective against cancer and we wanted to determine which form is more effective.'