Should you change your diet? - eating for cancer prevention - Preventing Cancer: What We Know Today

Surprising, but true. insights into a diet-cancer link first appeared back in 1913. At that time restricting calorie intake in laboratory rats was shown to inhibit the growth of cancer. That knowledge seems to have been largely ignored until more recently, when scientists again are uncovering the relationship between what we eat and our likelihood of developing cancer.

Most cancers are now believed to be caused by factors associated with lifestyle - in particular tobacco, alcohol, and diet. Up to one third of all cancer may be directly or indirectly diet related. Evidence centers on the fact that cancer occurs at different rates in different countries. These rates tend to change when people migrate from one country to another, suggesting that diet may play a significant role. Also, cancer rates differ among groups of individuals having different eating patterns. And animal studies have revealed several detrimental and protective effects of diet on tumor development.

Too many calories? Food restriction substantially reduces the incidence and size of tumors in laboratory animals. in humans, obesity is linked with a higher incidence of many types of cancer. The American Cancer Society has estimated that women who are 40 percent or more over ideal weight have a 55 percent greater cancer risk, and men 40 percent or more over ideal weight have a 33 percent greater cancer risk than those of normal weight. Simply stated, significantly obese persons have more tumors.

Too much fat? Populations eating less fat have less cancers, especially those of the colon, breast, pancreas, ovaries, and prostate. The question that is difficult to resolve: Is the problem caused by calories, or is it the fat?

In animal studies, increased feeding of fat increases the development of certain types of tumors. However, the promotion of cancer by feeding fat may be partly explained by the fact that fats provide essential nutrients called fatty acids needed for tumor growth. The relationship of fat intake to cancer growth is complicated because of the different food sources and chemical structure of fats, and because fats promote obesity.

When the diets and cancer rates are analyzed on a person-to-person basis, ambiguities arise. The Nurses Health study conducted at Harvard revealed that women who consumed high fat diets were no more likely to develop breast cancer than those whose fat intake was moderate. Few of the women, however, had fat intakes as low as those in countries where breast cancer rates are low.

In spite of a lack of consensus, many scientists believe that to whatever extent women can lower fat intake, they may be lowering breast cancer risk, as well as their risk for heart disease. It is also important for women to keep their fat consumption low after cancer surgery. Breast cancer patients who maintain a low fat diet increase their chances of successful recovery. Both the amount of fat eaten and the weight gain appear to influence the outcome. Women 25 percent or more above optimal weight and those with higher fat intake are at a significantly greater risk of tumor recurrence.

Reducing fat intake may also lower the risk of colon cancer. A high fat intake causes greater amounts of bile acids within the colon. While bile acids are necessary for fat digestion and absorption, these bile acids or their breakdown products may irritate the cells of the colon, promoting cancer.

Too little fiber? Although consensus on the relationship between dietary fiber and cancer has not been reached, fiber is considered to be an important preventive measure for cancer and other abnormal conditions of the colon. By eating more fiber, we may consume less fat and calories, because fiber-rich foods increase the bulk of our diet and contribute to satiety.

Fiber found in vegetables, fruits, and grains comes in two categories - soluble and insoluble. Soluble fiber is broken down by bacteria in the colon into substances that serve as nutrients for colon cells. Insoluble fiber has the ability to hold water, allowing the contents of the intestine to move rapidly through the large intestine. Fiber may dilute or minimize the harmful effects of bile acids or bile breakdown products, either by binding these substances or by lessening the time carcinogenic substances can do damage.

Increasing dietary fiber means eating more breads and cereals, more legumes (beans and peas), and more fruits and vegetables. Fiber can be increased by eating whole-grain bread instead of white, brown rice instead of white, and by biting into fruits instead of drinking them as juice. Such a diet will be lower in fat and calories, thus providing protection, whether or not it's the fiber that does the good work.

Too few fruits and vegetables? In over one hundred population studies, eating fruits and vegetables has been associated with a reduced cancer risk, particularly getting cancer of the lung, mouth, throat, stomach, colon, and breast. Unfortunately, most of us don't eat the minimum recommended daily amounts of these foods. What is in fruits and vegetables, other than fiber, that is protective? Recent attention has focused on their abundant content of certain substances that have antioxidant properties.

Antioxidants. Oxygen is vital to life and all bodily processes. But the natural activity of oxygen in the body produces free radicals, unstable molecules that damage cells and start a chain reaction that produces more free radicals. Free radicals are believed to initiate degenerative and mutating processes that result in cancer. Cells have systems to fight free radicals either by reducing their formation or by destroying them. Some of these free radical fighters (antioxidants) are made by the cells, and some are obtained from the food we eat.

Various substances contained in our food behave as antioxidants, including certain nutrients: vitamin A, beta-carotene, vitamin E, vitamin C, and selenium. Antioxidants in food protect against the damage of oxidation, permit the repair of damaged cells, and avert cancer development. When tested in animals, these substances have been found to reduce certain types of cancer.

To make sure you are getting an adequate supply of these antioxidants, you must eat the daily recommended amounts of fruits, vegetables, and whole grains. Health experts are cautious when it comes to supplementation, because excess amounts of vitamins and minerals can be dangerous.

Phytochemicals. in addition to antioxidants, plants contain a number of other substances that are potential antitumor agents. These have collectively been labeled phytochemicals (phyto-plant). Phytochemicals are biologically active substances found in commonly eaten plant foods. When tested, phytochemicals seem to block or suppress tumor formation by enhancing the ability of cells to fight cancer.

In order to get the maximum benefit of antioxidants and phytochemicals in plant foods, most of us need to double our intake of fruits and vegetables. It is also helpful to eat more legumes. Select from a variety, such as soybeans, tofu, lentils, peas, and garbanzos. Nuts may be eaten raw or lightly toasted (not salted or fried).

But how much you eat and what you eat may increase your risk of cancer.

People often look at cancer prevention as a supplement, or single diet change. "What specific food should I eat?" "What pill can I take?" Would that it were so simple! What is needed is lifestyle and dietary changes that are followed over time.

Ella Haddad, D.H.Sc., M.P.H., R.D., is an assistant professor of nutrition at the School of Public Health, Loma Linda University, Loma Linda, California.

Charred,

smoked,

salted,

pickled

foods

Cancer-causing substances form on some foods such as meats when cooked with high temperature on open flames. Saltcured or pickled foods may increase the risk of stomach and throat cancer. in countries where large amounts of salted foods are consumed, stomach cancer is more prevalent.

Where to Get Antioxidants

Nutrient Typical Food Source

Vitamin C (ascorbic acid) broccoli, citrus fruits and juice, red

and green peppers, cauliflower,

parsley, strawberries, cantaloupe Vitamin E whole-wheat foods, brown rice,

wheat germ, vegetable oil,

greens, almonds, hazelnuts,

sunflower seeds Carotenes apricots, carrots, spinach, broccoli,

kale, sweet potatoes, greens Selenium grains, legumes, nuts, vegetables,

mushrooms

Where to Find help

National Cancer Institute 9000 Rockville Pike Bethesda, MD 20892 1-800-4-CANCER

American Cancer Society 1599 Clifton Road, N.E. Atlanta, GA 30329 1-800-ACS-2345

American Institute for Cancer Research 1759 R Street NW Washington, D.C. 20069 1-800-843-8114

American Lung Association 1740 Broadway New York, New York 10019 1-212-315-8700

Hereditary Cancer Institute Department of Preventive Medicine/Public Health Creighton University 24th and California Streets Omaha, Nebraska 68178

Anticancer Substances

in Plant Foods

Phytochemical Typical Food Source

Aromatic isothiocyanate cruciferous vegetables (e.g.,

broccoli, bok choy, brussels

sprouts, cabbage, cauliflower,

collards, kale, mustard greens,

rutabaga, turnip greens, and

turnips) Dithiolthiones cruciferous vegetables Flavonoids fruits, vegetables, grains Indoles cruciferous vegetables Isoflavones soybeans, legumes Organo sulfides onions, garlic, leeks, shallots Phenolic acids soybeans, oats, apples, potatoes Protease inhibitor soybeans, seeds, nuts, legumes

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