Fish, especially oily ones, are great sources of omega–3 fatty acids. Research shows that this compound plays an important role in boosting the immune system, and helps to slow down the growth of tumours that are cancerous in nature. It also reduces chronic inflammation, which is a contributing factor towards breast cancer development. Salmon, trout, mackerel, etc., are all good forms of fatty fish. Consuming fresh and properly cooked oily fish, even thrice a week can be very beneficial.