Reducing Cancer Risks through Nutrition

"Your food shall be your remedy."

These words, written by Hippocrates more than 2000 years ago, hold true today as researchers continue to reinforce the connection between good nutrition and good health. More recently, noted English epidemiologists Sir Richard Doll, MD, DSc, and Richard Peto, MD, estimated that between 20% and 60% of cancer deaths were related to dietary factors. In other words, much of cancer may be preventable.

The American Cancer Society has long had an interest in the relationship of diet and nutrition to cancer. That nutrients play a role in various stages of carcinogenesis is clear, but the degree of that role and the specifics remain unclear. These are important issues with great public health implications. The Society also has recognized for some time that research on nutrition and cancer is complex, and progress comes with difficulty.

Increasingly, research is pointing to the important role nutrition plays in preventing or contributing to cancers. Researchers seeking to determine the optimal diet to reduce the risk of cancer and other major diseases have made important contributions that have helped the Society and other organizations develop nutritional guidelines. But the exact relationship between dietary ingredients and cancer is elusive, and many major questions remain. Among the complicating factors:

- the complexity of the diet in terms of biochemical components

- there are more than 100 types of cancers with different causes

- cancer takes many years to develop; therefore, it is hard to prove a cause and effect relationship

- dietary ingredients may increase as well as decrease the risk of cancer

In some kinds of cancer research, major advances may occur as the result of one publication, even one experiment. However, with nutritional research, because of the complexities, many advances are characterized by a new consensus of experts in the field Such a consensus requires consistency of data including studies of biochemical mechanisms, animals, and human populations, along with human clinical trials. The difficulty in making progress and the urgent need for more research only increase the Society's resolve to understand the relation between diet, cancer, and health.

The Link Between Fruits and Vegetables and Decreased Rates of Cancer

The Society's guidelines on diet and nutrition call for an ample and varied supply of fruits and vegetables in the diet, and numerous health agencies and nutritional experts concur with this advice. There are many reasons why there is so much support for a diet rich in fruits and vegetables. These foods are plentiful sources of vitamins, minerals, biochemical compounds, and fiber-ingredients that may help to reduce cancer, risk. Moreover, eating enough fruits and vegetables means an individual is likely to eat proportionately less fatty and high-calorie foods. Fruits and vegetables are chemically very complex, and contain many biochemicals that may contribute to reduction of cancer risk. Research underway in many laboratories is seeking to identify the factors in foods that help to prevent cancer.

The American Cancer Society's CPS-II study found that a diet rich in vegetables correlated with a significant decrease in risk of colon cancer in both men and women. This study, which followed 764,343 adults from 1982 to about 1990, is consistent with many other studies on vegetables or fruits and cancer, it contributed to the strong consensus in support of a diet rich in fruits and vegetables.

Much interest in prevention is focused on cruciferous vegetables like broccoli, cabbage, and cauliflower.

Vitamins, Nutrients, and Cancer Prevention

Paradoxically, while the Society recognizes the importance of the total diet and the interactions of dietary ingredients, it is also reasonable to expect that of the thousands of different substances in our diet, some ingredients are likely to be much more potent than others in helping to prevent cancer. There is currently a great deal of interest by the research community in antioxidant vitamins and nutrients. These chemicals interfere with oxidation, a process that can result in formation of carcinogens (chemicals that cause cancer). The carotenoids, which are related to vitamin A, are an example of dietary antioxidants.

The Facts About Fiber

Dietary fiber includes the components of fruits, vegetables, and whole grain cereals that are not readily digested, that is, ingredients of foods that resist breakdown by digestive enzymes. There are different kinds of fiber, and their merit in prevention may depend to some degree on the kind of fiber in question. A number of studies on human populations suggest that a high-fiber diet may help to prevent colon cancer. Not every study is supportive, but the evidence is such that recommendations for a diet with ample fiber are endorsed by the Society, NCI, United States Department of Agriculture, and the American Heart Association (AHA). Further research on the role of different kinds of fiber in prevention of cancer is in progress. It will also be important to determine whether the beneficial effects of high fiber foods are due to fiber content or to other ingredients in these foods.

Fat and Cancer: Current Knowledge

In general, animal studies suggest that a low-fat diet reduces overall cancer risk. Epidemiologic studies have been less conclusive and suggest that the risk of some kinds of cancer, such as colon cancer, may be more impacted by a low-fat diet than other kinds of cancer. The situation is further complicated by the fact that there are many kinds of fat, and some kinds of fat may have different effects on cancer risk than others. Fats may be saturated or unsaturated, and there are different kinds of saturated and unsaturated fats. Also, in high-fat diets, it is sometimes hard to distinguish whether an effect is due to the fat present or to the diet being high in calories.

While these gaps in knowledge are unsettling, the Society, along with the NCI and the AHA, emphasize the importance of avoiding a high fat diet. In the meantime, there is a major effort to clarify the role of fat in relation to cancer. To help people make educated choices about nutrition, the Society publishes nutritional guidelines to advise the public on dietary practices that may reduce the risk for cancer. The guidelines are meant to be practiced as a whole, creating a total dietary pattern to follow for lowered cancer risk.

- maintain a desirable body weight
- eat a varied diet
- include a variety of vegetables and fruits in the daily diet
- eat more high-fiber foods such as whole grain cereals, legumes, vegetables, and fruits
- cut down on total fat intake
- limit consumption of alcoholic beverages, if you drink at all
- Limit consumption of salt-cured, smoked, and nitrite-preserved foods.

In addition, several animal studies have already suggested that exercise may help to reduce risk for cancer.

Changing Behaviors to Prevent Cancer

Since cancer risk can be reduced by changing certain diet related behaviors, the more that is known about nutrition in relation to cancer, the greater the potential to reduce cancer risk. But knowledge about prevention does not necessarily translate to a reduction of cancer risk; such knowledge must be accompanied by changes in lifestyle. People often resist such changes, as evident from the fact that many continue to smoke, even after studies have confirmed a link between smoking and lung cancer. For many people, changes in behavior are extremely difficult, and more research on this subject is needed to help people live healthier lives.

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