THE LINK BETWEEN DIET AND CANCER

by Margaret Iverson

Every year, 1.2 million people are diagnosed with cancer and more than 500,000 people die from the disease. According to the National Cancer Institute, over 30% of these deaths can be attributed to diet. This means that the average person can greatly lower his risk of getting cancer simply by changing his diet. There is, of course, no guarantee against cancer, but the lifestyle choices that we make now can have a huge impact on our lives in the future. (http://www.aicr.org/expert1.htm)

What diet factors increase my risk of cancer?

     The majority of the studies done on the link between diet and cancer indicate that there is a relationship between high fat intake and an increased risk of cancer. High fat diets have been shown to increase the rates of breast, colon, and prostate cancer. But a low fat diet was not found to reduce the risk of cancer when compared with the average American diet of 30% fat. This is because calorie intake needs to be reduced along with the fat intake. A combination of low fat and low caloric intake is greatly effective in reducing the risk of acquiring cancer. (http://www.cc.columbia.edu./cu/healthwise/0913.html)
     Biologically, a low fat and low calorie diet makes sense. When excess calories are consumed, the body's metabolism is stimulated to divide cells more rapidly. With more cells being produced, there is a statistically greater risk of something going wrong during the dividing process. And since obese people have a larger number of cells in their bodies, there is a higher chance that one of these cells will become cancerous. (http://realtime.net/anr/dietcanc.html)
     Other diet factors affect your chance of acquiring cancer. For instance, high alcohol consumption increases the risk of mouth, larynx, esophageal, respiratory tract, and bladder cancers. Smoking added to excessive alcohol consumption increases the risk of these cancers even more. A maximum of four drinks a day for men and two drinks for women is recommended. Surprisingly enough, frequent consumption of smoked cured and nitrate preserved meats has also been shown to cause cancer. The codes of 249, 250, 251, and 252 on labels of corned beef, bacon, and smoked sausage indicate that the meat has been cured or preserved. These products increase the risk of stomach cancer and should be eaten in moderation. (http://www.petermac.unimelb.edu.au/DIET.html)

What are the dietary guidelines for reducing my risk of cancer?

1. Eat at least 5 servings of fruits and vegetables every day.
A plant-based diet is high in fiber, minerals and vitamins. The American Cancer Society is quick to point out that you should not need to take extra vitamins if you are eating five servings of fruits and vegetables every day. Citrus fruits, berries, and tomatoes are good sources of vitamin C. Beta-carotene is found in vegetables such as spinach, broccoli, cauliflower, brussel sprouts and cabbage. Cruciferous vegetables may have cancer preventative properties. Since fruits and vegetables are inherently low in fat, eating them often will also help keep your fat intake down.
2. Eat high fiber foods.
Eating foods high in fiber will help keep your colon clean and cut your risk of developing colon cancer. Without fiber, digested food in the colon will remain there, allowing the bacteria in the food to infect the cells of the colon. Fiber produces “bulk” which helps keep everything running smoothly through the body. Five servings per day of foods such as whole grain bread, whole-wheat bread, and cereals will provide sufficient fiber in your diet.
3. Limit fat intake.
This is especially important. For more information on this subject, look under the heading, “What diet factors increase my risk of cancer?”. You can keep your fat intake down by making simple changes in your diet. One easy way to cut your fat intake is by eating lean meats such as lean chicken, turkey, and fish. Legumes, beans, and low fat cheeses may even replace the one serving of meat per day recommended by the American Cancer Society. Use limited amounts of greasy salad dressings, spreads, and sauces. By following these simple suggestions, you should be able to cut a significant amount of fat out of your diet and therefore reduce your risk of cancer. (http://petermac.unimelb.edu.au/DIET.html)
4. Stay or become physically fit.
Obesity has been found to greatly increase the risk of cancer. It is recommended to get at least 30 minutes of exercise each day to maintain a healthy heart and body weight. Maintaining a healthy body weight not only lowers your risk of cancer, but also decreases your chance of heart disease, stroke, and heart attacks.
5. Limit consumption of alcohol.
If you drink at all, remember to limit it to four drinks per day for a man or two drinks per day for a woman. A number of different cancers are known to be caused by the use of alcohol, such as mouth, larynx, esophageal, respiratory tract, and bladder cancers.
(http://www.cancer.org/guide/guidredu.html)
(http://www.petermac.unimelb.edu.au.DIET.html)
(http://www.cc.columbia.edu./cu/healthwise/0913.html)

What studies can be found on the Internet which deal with the effects of diet on cancer?

        In 1982, the first study by the American Cancer Society was conducted. This study provided the information needed to set the first dietary guidelines for preventing cancer. Since then, the American Cancer Society has reviewed the guidelines approximately every five years. The society's recommendations have not changed significantly because research continually supports the current guidelines. (http://www.cancer.org/guide/guidwhy.html)
     Research regarding the importance of specific dietary factors has just started to emerge. Lillian Thompson, Ph.D., is currently researching whether flaxseed can prevent breast cancer and if it can reduce the size of a tumor. Thompson, a professor at the University of Toronto since 1969, is conducting a prospective study of 100 post menopausal women who have recently been diagnosed with breast cancer. Half of the women receive a muffin with 25 grams of flaxseed every day and the control group receives a placebo muffin with no flaxseed. Thompson hopes to demonstrate the ability of flaxseed to affect tumor growth. This study is funded by the American Institute for Cancer Research. (http://www.aicr.org/m53.html)
     Another study that is being funded by the American Institute for Cancer Research is on the importance of retinoic acid (RA), a form of vitamin A, in the prevention and development of colon cancer. Dr. M.A. Christine Pratt is researching whether retinoic acid can regulate the growth of cancer cells by controlling the genes that cause breast cancer. She is currently studying the effects on animals, but hopes to eventually apply her study to human subjects to determine whether it can permanently prevent cancer growth. (http://www.aicr.org/m53.html)

What research has been done to support the dietary guidelines?

    Fat and Caloric Intake
    In a study by Albert Tannenbaum (1940), it was found that restricting caloric intake and underfeeding lowered the incidence of cancer and delayed the onset of cancer in cancer-susceptible mice.¹ Tannenbaum and Silverstone went on to show that actuarial information in the United States related to the animal data.² The actuarial data showed that cancer-related deaths were directly related to obesity. Inversely, underweightedness led to a lower rate of death from cancer.

    Role of Vitamin A
    The case-control studies by Mettlin (1979), Colditz et al. (1987), and Byers et al. (1987) all show that vitamin A is directly related to a reduced risk of lung cancer.³ Two other well-respected long term prospective studies on the role of vitamin a were done in Norway by Bjelke (1975) and Kvale et al. (1983). These researchers gave questionnaires to men which measured their intake of vitamin A. It was found that men with low vitamin A consumption had a higher incidence of lung cancer than those men who had high consumption of this vitamin.⁴
    In 1979, Hirayama conducted a prospective study of 256,118 Japanese citizens. Hirayama observed the subjects' dietary patterns in order to determine causes of mortality. He found that green and yellow vegetables (which contain vitamin A) had a preventative effect on lung cancer. Note: the confounding variable of cigarette smoking was carefully considered when determining the effects of diet on lung cancer in order to prevent any false outcomes.⁵

    Special Considerations
    When looking at studies done on the link between diet and cancer, you must take into consideration the limitations of the study. Different research designs provide different levels of proof and should therefore be weighed differently in significance. The type of study with the highest level of proof is an intervention trial. While this type of trial is highly accurate, it is also expensive, time consuming, and requires much expertise and effort. Since it is not always practical to perform an intervention trial, less accurate design types are used such as correlational, case-control, and prospective studies. These designs are more practical because they have low to moderate costs, amounts of time required, and level of expertise required to perform the study.⁶

The link between diet and cancer is just beginning to be understood. By following the guidelines provided, the risk of cancer can be greatly reduced. Nothing can completely prevent the disease, but these guidelines should help. As new research begins to emerge we will understand more and more about the connection between the foods we eat and their effects on our health.⁷ Scientists don't currently know which specific foods we should eat to prevent cancer. In the future we may be able to control cancer, along with many other diseases, simply by consuming a specific combination of foods.

REFERENCES

1. Petering, H.G. (1986) Diet, nutrition and cancer. Progress in Clinical and
    Biological Research 222:207-229.
2. Petering, H.G. (1986)
3. Mettlin, C. (1987) Levels of epidemiological proof of diet and cancer with
    special references to dietary fat and vitamin A. Progress in Clinical and
    Biological Research 259:149-159
4. Mettlin, C. (1987)
5. Mettlin, C. (1987)
6. Mettlin, C. (1987)
7. Yang, C.S., Pence, B.C., Wargovich, M.J., and Landau, J.M. (1996) Diet,
    nutrition, and cancer prevention. Advances in Experimental Medicine and
    Biology 401:231-8

Send questions and comments to:
margaret.e.iverson@vanderbilt.edu

last edited: 11/11/97

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