by John Weisberger, PhD

Over the past 50 years we have learned much about how diet affects cancer risk. If Americans adopted the current dietary guidelines issued by the
National Cancer Institute, cancer rates would decrease by as much as 25
to 50%. Plant foods are protective for several reasons.

Fiber Reduces Cancer Risk

Early interest in fiber and cancer came from intriguing observations
of the Finnish population

1. The people in Finland have one of the highest rates of heart attacks, but they have relatively low rates of both colon and breast cancer. Dietary studies showed that the Finns are high consumers of dairy products including milk, which may contribute to their high rate of heart disease. However, they also consume a type of rye bread high in bran fiber. When investigators studied stool samples of Finns and compared them to those of people living in New York (the researchers collected and studied stool specimens from 40 individuals from each country) they found that stools of Finns weighed two to three times more than those of New Yorkers. Also, the concentration of bile acids in Finnish stools was much lower than that in the American stools. Bile acids are compounds produced by the liver to aid in the digestion of fats but they also appear to promote the growth of cancer cells in the colon.
   
   The larger stool also increases the excretion of estrogen and therefore
   could result in lower blood estrogen levels in Finnish women. This may protect against breast cancer, since lower estrogen levels are associated
   with reduced risk for breast cancer.
   
   About the same time that the Finns were being studied, Dr. Denis Burkitt,
   a distinguished British surgeon stationed in Uganda, noted that colon
   cancer rates were high among British living in Africa but rare among native
   Africans
   
   
2. In fact, the Africans rarely had any intestinal diseases such as appendicitis, diverticulosis, and irritable bowel syndrome. Dr. Burkitt found that, compared to the British, the Africans ate more high-fiber
   cereals and lots of fruits and vegetables--a fiber intake as high as 70 grams a day compared to 15 grams per day which is common intake among
   westerners. They generated multiple stools every day, weighing as much
   as 10 to 15 ounces.
   
   Fiber helps to reduce colon cancer in two ways. Bran cereals and high fiber breads contain mostly insoluble fiber, which absorbs fluid and swells up to provide for increased stool bulk. This helps to decrease the concentration of harmful bile acids and other potential carcinogens in the stool. Oat bran and many vegetables contain mostly soluble fiber. This doesn't add much to stool bulk but forms a gel-like matrix that aids in the elimination of bile acids and other potentially harmful components in the colon.
   
   Fiber is extremely important in reducing risk for colon cancer.
   In 1978, when the Food and Drug Administration (FDA) initiated a ban on the artificial sweetener saccharin, I noted that the American people would
   be better off if the FDA banned white bread
   
   
3. In view of what we know about fiber and cancer risk, it is indeed important to consume a diet high in cereals, whole grain breads, fruits and vegetables.
   
   Phytochemicals and Antioxidants: The Power of a Fruit and Vegetable Diet
   
   International comparisons and comparisons within countries show that
   people who eat green and yellow vegetables and fruits have a lower incidence of major chronic disease, including many types of cancer. More than 200 studies show the benefits of fruits and vegetables. The immediate thought that comes to mind is that vegetables and fruits are good sources of vitamins and minerals
   
   
4. However, vegetables and fruits contribute much more to good health than just vitamins. They are sources of phytochemicals-or plant chemicals-which are not nutrients, but are biologically active compounds. Just as humans produce antibodies to ward off infection, phytochemicals offer protection to plants. They may also be protective for us
   
   
5. There are many different types of phytochemicals in plant foods. These include indoles in vegetables of the cabbage family, sulfur compounds in garlic and leeks, isoflavones (plant estrogens) in soybeans, lignans in flax seed, and carotenoids in many vegetables. Phytochemicals appear to exert physiological effects in many different ways
   
   
6. They may stimulate the immune system, help to detoxify harmful chemicals, affect hormone levels, and control cell growth. But of particular importance is the action of some phytochemicals as antioxidants.
   
   Why is this significant? Living cells require oxygen because the enzymes
   that generate the energy essential to cell functioning require oxygen.
   But during the process of oxygen use, cells can also generate abnormal
   reactive chemicals. Some of these reactive oxygen components are potentially dangerous and may lead to heart disease or initiate cancer. Nature has provided for neutralization of these potentially harmful components by supplying antioxidants in food and drink.
   
   Some Fats Raise Cancer Risk
   
   As long ago as the 1940s, a few early pioneers suggested that dietary fat played a role in enhancing cancer risk. However, their research was not considered "fashionable" by mainstream cancer researchers and was largely ignored until the mid-1960s. At that time, Canadian researcher Kenneth Carroll showed that laboratory animals fed a 40% fat diet (similar to what westerners eat) had a much higher rate of breast cancer compared to those fed a 10% fat diet
   
   
7. Later research at the American Health Foundation (AHF) in New York confirmed these findings.
   
   The studies at the AHF were inspired by the dramatic differences in breast
   cancer rates between women in the United States, whose fat intake averaged about 40%, and those in Japan, whose fat intake was closer to 10%. But women in Italy also had relatively lower cancer rates despite a fairly high fat intake. This gave rise to questions about type of fat as well as amount of fat in the diet
   
   
8. Further studies showed that high intakes of animal fat and of polyunsaturated oils like corn or safflower oil increased the number of breast and colon tumors, compared to low-fat intake. A high dose of corn oil, for example, led to increased synthesis of bile acids, the compounds that raise risk for colon cancer.
   
   Other types of fat had different effects, however. The omega-3 fatty
   acids found in fish oils and some plant foods actually reduced the incidence of breast and colon tumors, while monounsaturated oils such as olive oil were neutral. Although it hasn't been tested, canola oil, which is high in monounsaturated oil and contains some omega-3s, is likely a lower risk oil than other vegetable oils. The same may be true of flax seed oil, which is high in omega-3 fats. Both monounsaturated and omega-3 fats may also protect against heart disease. This would help to explain the lower rates of both cancer and heart disease in southern Italy and Greece
   
   
9. Even though these diets are relatively high in total fat, much of the fat in the cuisines of these countries is monounsaturated or rich in omega-3 fatty acids.
   
   Other Food Components May Raise Cancer Risk
   
   Cooking meat to the well-done stage involves the generation of reactive
   chemicals called heterocyclic amines. These chemicals, formed during browning of meat, may increase the risk of cancer of the colon, breast, prostate, and pancreas. Red meat appears to be particularly harmful
   
   
10. The use of salt and pickled foods, common in many types of Asian cuisine, raises risk for stomach and esophageal cancer
    
    
11. Conclusion
    
    Early humans consumed foods that were freely available from nature-wild
    fruits, berries, greens, seeds, and roots. They may have used some milk
    from lactating animals but ate little meat. In modern times, many cultures
    have adopted a meat-and-potatoes diet with excessive amounts of salt.
    
    Scientific research has produced a sound basis of knowledge for producing
    guidelines for a healthy lifestyle in order to reduce risk for cancer
    
    
12. Western eating habits are based on the wrong foods-too much
    of the wrong kinds of fat, too much meat with dangerous heterocyclic amines, too many salted foods, too little dietary fiber, and too few fruits and vegetables. Healthier eating habits should include generous use of fruits and vegetables-5 to 10 servings a day should be a goal, and foods such as cooked tomatoes and soy products should be used frequently. Foods high in fiber such as cereals, whole grain breads, and legumes should also be a regular part of the diet. And, choosing sources of monounsaturated fat and omega-3 fatty acids over animal fats and other plant fats should be a goal. Here at the American Health Foundation, our research goal is to "allow us to die young as late as possible."
    
    

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Dr. John Weisburger has conducted research on prevention and cancer and
has published over 500 papers. He is a past Director of the Research Institute of the American Health Foundation in Valhalla, New York.