Olive oil: A healthy dietary fat, olive oil is rich in monounsaturated fats and antioxidants. An analysis of cancer studies over the last 11 years found that high intake of olive oil correlated to lower odds of developing any type of cancer--including breast cancer.
Omega 3s: Essential fatty acids, omega 3s are found in oily fish such as mackerel, sardines, albacore tuna, and salmon as well as in supplement form. Research indicates that women who eat foods rich in omega-3 fatty acids may be less likely to develop breast cancer.
Fiber: If you're eating your fruits and vegetables, you've got a good start on a high-fiber diet. Now add whole grains to boost your intake. The effect could be significant: A team of nutritionists in China gathered research from 10 earlier studies on women's diets and cancer risk and found that women who consumed the most dietary fiber were 11 percent less likely to develop breast cancer than those who ate the least.
The same review determined that every 10-gram-per-day increase in dietary fiber intake was associated with a 7 percent reduction in breast cancer risk.