Research studies evaluating the relationship between diet and cancer show conflicting results. However, the studies have consistently shown that people who are more than 40% overweight have an excess risk of certain types of cancer, especially of the uterus, gallbladder, kidney, colon, prostate and breast.
In general, the American Cancer Society recommends a diet low in saturated fat and high in fiber, with particular emphasis on eating fresh fruits and vegetables, reducing salt-cured, smoke-cured and nitrate-cured foods, and limiting how much alcohol you drink. Alcohol consumption of greater than two drinks per day is associated with several different cancers. Breast cancer risk is increased with any alcohol consumption, but the good news is that keeping alcohol intake to one drink per day or less combined with taking 400 micrograms of folic acid each day keeps the risk almost at baseline. The risk of liver cancer increases with the onset of cirrhosis. Throat, neck, and esophageal cancer are clearly related to regular overuse of alcohol, especially if combined with smoking.
The American Cancer Society stresses a diet of high fiber foods. The healthiest of the high-fiber foods are ones that contain whole grain ingredients. Other foods high in fiber are beans and legumes, such as chick peas, black beans, broad beans, kidney beans, lentils and pinto beans; dried fruits like dates, figs, prunes and raisins; fresh fruits, especially apples, pears, raspberries, blueberries, blackberries and strawberries; and fresh vegetables, particularly squashes, snow peas, uncooked spinach leaves and baked potatoes (with the skins left on).
The best way to adjust to a high fiber diet is to first increase your fiber content gradually; otherwise, you may suffer cramps and unpleasant gas. It is also important to drink eight glasses of liquids per day (water, fruit juices and sodas count, not including tea or coffee because of their diuretic effects). If you don't, you will likely find yourself constipated, despite the high fiber intake.
The National Cancer Institute also endorses a diet low in saturated fat and high in fiber. And the NCI also recommends eating more than five servings of fruits and vegetables per day. Their dietary guidelines include minimizing consumption of salt-cured, salt-pickled and smoked foods; consuming alcoholic beverages in moderation, if at all, and avoiding obesity.
Fruits and vegetables rich in carotenoids probably reduce the risk of cancer. For foods rich in carotenoids, think particularly about dark yellow or orange fruits and vegetables, and green leafy vegetables, such as dried apricots, cantaloupe, carrots, cooked collards, uncooked spinach leaves, fresh parsley, peaches, pumpkin and sweet potatoes. One particular cancer where diet might have a big impact is colon cancer. Studies suggest that individuals who stick to a diet low in saturated fats and high in fruits, vegetables and grains have lower risk of colon cancer. Preserved meats (such as bacon, cured ham, hot dogs and salami) may contribute to colon and rectal cancer. And lean, fresh meat may be less of a problem than previously reported. The "dietary risk factors for colon cancer story" continues to evolve, though the message is the same: concentrate on the fruits, vegetables, and whole grain foods. Good sources of protein are soy, egg whites, nuts and poultry.
Men may be able to decrease their risk of prostate cancer by eating less saturated fats and eating more cooked tomatoes. A study of Italian men found that those who had increased their consumption of tomato sauce had a decreased incidence of prostate cancer. Cooked tomatoes release the phytochemical lycopene, a substance with antioxidant properties.