A healthy diet can help the body in its efforts to heal itself, and in some cases, particular foods can strengthen the immune system and lessen the risks of serious illness. To help reduce your risk of some types of cancer, try the following:
Avoid polyunsaturated vegetable oils, margarine, vegetable shortening, all partially hydrogenated oils, and all foods that might contain trans-fatty acids (such as deep-fried foods).
Increase omega-3 fatty acids by eating more cold water oily fish, freshly ground flaxseeds, and walnuts.
Reduce consumption of animal foods and try to replace them with vegetable proteins such as whole soy products.
Use hormone-free, organically produced products whenever possible.
Eat plenty of fresh fruits and vegetables.
Eat shiitake, enokitake, maitake, and oyster mushrooms frequently.
Drink green tea daily.
...from Dr. Weil website