Some foods actually contribute to the development of cancer; other foods lessen the risk. The following anti-cancer diet greatly lowers your risk of colorectal cancer and nearly all other types of cancers. It can also prevent cardiovascular disease. For people with a genetic tendency toward colorectal cancer, it is not just an option, it's a lifesaving necessity.
Keep your diet low in total fat and very low in saturated fats. There are at least two ways in which dietary fat contributes to cancer. First, tumor cells need low density lipoproteins (LDL's) to grow. Therefore, a diet that helps to lower LDL levels could keep potentially cancerous cells from growing. Eating fat also stimulates the production of bile, which is needed to digest fat. If a lot of bile is allowed to stagnate in the large intestine for a long period of time, it's converted into apcholic acid, a proven carcinogen. Here are tips for eating not only less fat, but eating the right fats:
Eat less total fat. Limit your daily fat intake to no more than 20 percent of your total food calories. This means that if you average 2,500 calories a day, fat should provide no more than 500 of these calories. This means you should eat around 55 grams of fat per day, maximum. (On a 2,000 calories per day diet, you would eat about 45 grams of fat.)
Eat the right fat. Eating the wrong kinds of fat may be even more cancer-causing than eating too much fat. Cancer researchers became aware of this fat fact when they noticed that the incidence of most cancers is less in some cultures who actually have a high-fat diet, such as Eskimos (who eat a lot of seafood rich in omega 3 fatty acids) and the Mediterranean diet (which is plant-based, but high in monounsaturated oils). Some fats don't contribute to cancer and may in fact have some anticancer properties:

1. Unsaturated fats, found in plant foods, such as legumes
2. Vegetable oils that are high in monounsaturated fats, such as olive (Greek women who tend to eat a diet rich in olive oil have a very low incidence of breast cancer) and canola oil. A 1998 study showed that men who eat less animal fat and more vegetable fat in their diets had less prostate cancer.
3. Seafood, such as salmon and tuna, that is high in omega 3 fatty acids
4. Oils that contain more omega 3 than omega 6 fatty acids, such as flaxseed, pumpkin seed, canola, soybean (not hydrogenated), walnut, sunflower, sesame, and virgin olive oils. (Heating vegetable oils at high temperatures can change fatty acids and make them carcinogenic. Peanut oil and extra virgin olive oil stand up best to cooking, but try not to boil them. It helps to keep stirring stir-fry’s so the oil doesn't get burnt.)

Studies in experimental animals showed that fish-oil-supplemented (high in omega 3 fatty acids) animals had significantly fewer colorectal tumors. Omega 3 fatty acids (such as those found in fish oils and flax seed oil) are not only the heart-healthiest fats, but they may have anticancer properties.
Don't eat bad fats. Avoid oils high in saturated fats, such as palm, palm kernel, coconut, and cottonseed oils. Hydrogenated fats (those that have been chemically changed from unsaturated to saturated fats), are potentially carcinogenic. Adding hydrogen to a fat molecule may enable the molecule to interfere with the normal metabolism of cells in the body, setting the cell up for cancerous changes. So get used to reading labels. If any food contains "hydrogenated" or "partially hydrogenated" fats, leave it on the shelf. Most fast-food outlets use hydrogenated fats. Ask! If they do, don't eat the food.) Nearly all packaged foods, such as potato chips, contain hydrogenated fats, since these allow a longer shelf life.