After decades of research, papers, conferences, and head-scratching, scientists have concluded that what we eat contributes to about 60 percent of the cases of cancer in American women and 40 percent in American men. As scary as this may sound, it also provides a wonderful opportunity for prevention, since the reverse is also true: By eating wisely, we can reduce our odds of contracting this most dreaded of diseases.
Researchers have now learned enough about the role that nutrition plays in many forms of cancer to make some very specific recommendations on ways to fend them off. If a certain type of cancer runs in your family, a few highly targeted changes in your diet could, in years to come, literally save your life. Remember, a genetic vulnerability to cancer doesn’t make it inevitable. Any nutritional measures you can take against it are well worth the effort.
Basic Rules of Thumb
Whatever type of cancer concerns you, there are a handful of simple guidelines for prevention that apply across the board: Eat more fresh fruits and vegetables, more whole grains, and much less fat than most Americans eat today—and keep your weight in check. (A study of more than a million men and women by the American Cancer Society has shown that obesity leads to higher death rates from cancers of the gallbladder, bile duct, breast, uterus, and ovaries.)
It seems that America’s parents were ahead of their time in urging kids to eat their vegetables: Most experts do agree that consuming a lot of vegetables may be one of the best ways to prevent cancer. Those vegetables, though, shouldn’t lie on the plate leaking water like a wet bathing suit. They need to be steamed, microwaved, stir-fried, or otherwise cooked in little or no water and served crisp, perhaps with a tasty low-fat sauce.
Scientists continue to debate the value of specific ingredients in foods. For example, some observers of the effects of nutrition are convinced that ingesting more antioxidants such as vitamins A, C, and E—in food and in supplements—is the best available answer to preventing cancer and fighting its spread in the body. (Antioxidants combat the oxidation of molecules in cells. For more on these substances, see “Food That Fights Cancer.”)
Other experts remain cautious, pointing out that the benefits of eating fruits and vegetables may be derived from something else they contain. “The jury is still out on antioxidants,” says Carolyn Clifford, Ph.D., chief of the Diet and Cancer Branch at the National Institutes of Health. “Some studies have found a slight increase in cancers, such as lung cancer, among people taking supplements.”
More than 1,000 compounds that may discourage cancer have already been identified; one or more could conceivably be found to pack more anti-cancer power than antioxidants. The bottom line is that in more than 100 research studies, people who ate a lot of fruits and vegetables were only about half as likely to develop cancer as those who rarely ate those foods.
In general, the key to cutting your odds of cancer through nutrition seems to have two components: avoiding foods that help tumors grow and concentrating on foods that fight such growth. Neither route alone is enough. Here’s a summary of ways to work toward preventing specific types of cancer with every meal and snack.
Dietary Recommendations From The American Cancer Society
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Breast Cancer
Breast cancer is greatly feared, and rightly so, as the most common cancer among American women. Your chances of contracting the disease are greater if a close female blood relative has had it. In addition, although breast cancer strikes more women after age 50 than before, thousands of women under 50 are diagnosed with it each year. But whether there is a history of breast cancer in your family or not, you can definitely improve your chances of avoiding it by following a few nutritional rules.
Until recently, most experts believed that a high-fat diet was one of the main culprits in breast cancer. They theorized that dietary fat easily becomes body fat; and body fat produces extra estrogen. In turn, high levels of estrogen circulating through the blood can apparently help certain tumors grow in the breast and reproductive tract. But a major study that tracked the development of breast cancer in nearly 89,000 American nurses recently failed to find a link between a high-fat diet and invasive breast cancer—the kind that affects the breast and at least one nearby lymph node. Worse yet, when Harvard researchers measured blood estrogen levels in postmenopausal women, they found that as total dietary fat increased, estrogen levels actually went down, suggesting that—at least in women who are past their child-bearing years—total fat intake doesn’t increase the risk of estrogen-dependent breast tumors. Similarly, an analysis of several studies, involving almost 340,000 women in four countries, was unable to find a positive link between total fat intake and breast cancer.
Consistent with those findings, the American Cancer Society recently concluded that “The current view is that the type of fat in a woman’s diet may be more important than the total fat intake.” This position is backed by substantial evidence. In the Harvard study, the only type of fat that seemed to increase estrogen levels in postmenopausal women was the trans fats. (These are the fats formed when vegetable oil is solidified by partial hydrogenation.) Similarly, new research strongly suggests that monounsaturated fats—the kind found in olive and canola oils—protect against breast cancer while polyunsaturated fats—found in corn oil and many tub margarines—and the saturated fats in meats increase the risk of breast cancer.
Like monounsaturated fats, fiber seems to reduce the risk of breast cancer. It is thought to impede the body’s absorption of “bad” fats, in turn reducing the production of estrogen. It also helps speed cancer-causing substances that have reached the intestines through and out of the body before they can cause serious damage. (For more on fiber, see the box “Fiber: There’s More to the Story than Bran.”)
Women who eat extra fiber also rid themselves of more of their excess estrogen in bowel movements rather than in urine. This is important because estrogen in the urine can be reabsorbed into the bloodstream and eventually reach the breasts and other organs vulnerable to hormone-related cancer. Dietary fiber “binds up” estrogen as it enters the small intestine, and may do the same with other cancer-causing agents, preventing them from being absorbed through the intestinal wall into the bloodstream where they can be carried to the breasts.
Other foods defeat the harmful effects of estrogen by displacing it within the body. Plant-based estrogen-like substances in soybeans and soybean products (including tofu) are believed to have a protective effect. These “phytoestrogens” are thought to compete with the body’s own estrogen for binding sites in breast tissue. Once there, the plant-based estrogens may block the attachment of the more potent human hormone to the breast cell receptors, thereby combating the hormone’s cancer-inducing effects.
A growing number of experts are becoming concerned, however, about women who take concentrated doses of these phytoestrogens in pill form. In Japan, the phytoestrogens in soy products are thought to be at least partially responsible for the country’s low rate of breast cancer. But in the U.S., the unusually high doses now available in some over-the-counter herbal products may actually _increase_the risk of the disease by exerting an effect similar to that of human estrogen. Some capsules, for instance, contain as much as 500 milligrams of isoflavones—a potent phytoestrogen—while the typical Japanese woman consumes no more than 50 milligrams a day in soy-based foods like tofu.
Additional foods that seem to deter breast cancer in one way or another include green vegetables, omega-3 fatty acids in oily fish, omega-9 fatty acids in olive oil, wheat bran, and cruciferous vegetables, such as cabbage, bok choy, and brussels sprouts.
Some studies have found lower rates of breast cancer in geographic areas where the water and food contain ample amounts of selenium. But the authors of The Doctors’ Anti-Breast Cancer Diet, among many others, advise against taking selenium supplements as a hedge against breast cancer, because it can be toxic in large amounts. Do consider taking a daily multivitamin, however, containing a modest amount of selenium. The best sources of selenium are foods such as fish (especially sardines), whole wheat, wheat germ, whole grains, mushrooms, asparagus, and garlic.
Vicki L. Seltzer, M.D., writes in Every Woman’s Guide to Breast Cancer, “At present, dietary modification appears to be in the vanguard of our attempt to decrease the risk of breast cancer, as well as other malignancies and a variety of other serious illnesses.”
Here are five ways to protect yourself:
1. Eat a low-fat diet. Be especially sparing with saturated and polyunsaturated fats. Keep total calories from fat below 30 percent, and try to get half of those from monounsaturated fats. Remember that holding down total calories is important too. Exercise to burn off any excess.
2. Eat foods rich in antioxidants. Consider taking antioxidant supplements as well, especially if you smoke or are under considerable stress. (But beware of overdose.)
3. Keep your waist trim. Studies indicate that the location of body fat matters. A waist- to-hip ratio above 0.8 may increase cancer risk. Aim for a “pear shape” rather than an “apple shape.”
4. Monitor estrogen levels. Be sure your doctor does periodic blood tests, especially if you take birth control pills.
5. Limit alcohol intake. Alcohol has been linked with breast cancer.
Where Dietary Changes Make The Most Difference | |||
| For people at higher-than-average risk of a particular type of cancer, nutritional science now offers specific menu items that can help fend it off.If breast cancer runs in your family, for instance, consider increasing your intake of fiber, soybean-based foods like tofu, and vegetables in the cabbage family. The fiber helps flush cancer-promoting estrogen from the body; harmless chemicals in the soy products displace estrogen; and the vegetables supply other cancer-inhibiting agents.Likewise, if the possibility of colon cancer is a special concern, you should boost your intake of fiber and calcium. The fiber binds with potentially cancer-causing chemicals and hurries them through the colon; calcium helps maintain the health of the colon's delicate inner lining.Other threats that can be discouraged by specific dietary improvements are cancers of the lung, liver, stomach, esophagus, and oral cavity. |
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Prostate Cancer
Once unmentionable in public but now much in the limelight, prostate cancer is often fatal unless it’s diagnosed in its early stages. The prostate gland, which secretes male seminal fluid, is strongly affected by hormones, so dietary prevention strategies against prostate cancer are similar to those for breast cancer, although research is far from complete.
Some studies suggest that eating foods low in fat and high in antioxidants (especially vitamin A, selenium, and possibly fish oils) and vitamin D provides the most likely nutritional route for lowering the odds of prostate cancer. One of the most encouraging studies linking nutrition to prostate cancer involved selenium. Searching for a way to prevent skin cancer, researchers gave a daily dose of 200 micrograms of the trace element to healthy adults with a family history of the disease. While the selenium had no impact on skin cancer, it did produce a significant reduction in the incidence of prostate cancer.
Fat doesn’t seem to cause the cancer, but it does promote the growth of tumors once cancer gets started. In particular, keep to a minimum saturated fats such as beef, processed meats, butter, and whole milk.
Since the risk of developing prostate cancer increases if you are overweight, remaining trim and fit should also help reduce your risk. Men who weigh at least 20 percent more than is standard for their height, body type, and age, have a four times greater risk of prostate cancer than men of standard weight.
Colorectal Cancer
The last 5 or 6 feet of the intestine—the colon—join with the 5- to 6-inch rectum to create the large bowel. This is the area referred to in the term “colorectal cancer.” The latest statistics show that about 130,000 Americans develop this cancer each year and 56,000 die from it annually, making it the second leading cause of cancer-related deaths in the U.S.
Along with the breast, the colon ranks high among the organs in which the odds of cancer can be dramatically reduced by nutrition. In a field noted for caution and hedging, a 1991 report by researchers at the University of Southern California, Los Angeles, stated outright, “Dietary changes can reduce the risk of developing large bowel cancer.”
A high-fat diet (especially one high in animal fats) increases the risk of colorectal cancer. Meat-derived fats seem to be especially risky because they increase the formation of cancer-causing nitrosamines in the intestinal tract. When healthy men were fed diets containing either no meat or large amounts of it, the meat-eating group showed a fourfold increase in the amount of nitrosamine-related compounds found in the stool.
If a high-fat diet is combined with a low intake of fiber, the risk becomes even greater. Some scientists estimate that if Americans reduced their consumption of animal fats by 50 percent, the number of cases of colon cancer would decrease by the same amount.
A high-fat diet increases the amount of bile acids and bacterial enzymes in the colon, where bacteria can convert them to cancer-causing chemicals. Increasing the amount of fiber in the intestines helps to reverse this effect by diluting or inactivating the chemicals and reducing the level of bile acids and bacteria.
Another important function of fiber is to keep wastes and their cancer-causing byproducts flowing quickly so that they’ll leave the body before they have much time to come in contact with the sensitive cells that line the inner walls of the bowel. In a typical American diet, food takes three days or more to pass through the bowel. Eating even less fiber can allow food to remain in the body still longer. With a high-fiber diet, food is eliminated in a day or two.
While most health authorities believe that a high-fiber diet reduces the risk of a variety of diseases, two recent clinical trials have called into question its value in preventing colorectal cancer. In one study, a large group of volunteers with a history of precancerous colorectal polyps were either put on a low-fat, high-fiber diet rich in fruits and vegetables or allowed to continue their normal diet. After four years, there was no difference in the number of recurrent polyps between the two groups.
In a similar study, when high-risk patients were given either a low or high dose of wheat bran, investigators were unable to find any difference in the frequency of precancerous growths three years down the road.
These results certainly cast a degree of doubt over fiber’s importance in the fight against colorectal cancer. However, critics of the studies point out that all the volunteers were on a high-fiber diet for a relatively short time—three to four years. Most cancers develop very slowly over many decades, so it’s likely that preventive measures would be needed for a comparable period of time to significantly reduce the threat of the disease.
The amount of fiber used in the studies could also be a problem. Critics warn that it may not have been high enough to actually protect against cancer. In one of the investigations, for instance, high fiber was defined as 18 grams per 1,000 calories, though some experts now suggest that Americans would benefit from 50 grams of fiber a day or more. Experiments using a fruit, vegetable, and nut-laden diet that contained 55 grams of fiber per 1,000 calories caused the amount of bile acids in the stool to shoot up significantly. The more bile acids that can be forced out of the intestinal tract, the less that will remain to encourage tumor formation.
Most experts continue to recommend about 20 to 30 grams, or just under an ounce, of fiber each day. Most Americans consume only half that amount. One way to get your fiber is to eat a bowl of high-fiber wheat bran cereal every day, or its fiber equivalent. But read labels carefully; most cereals are not high in fiber.
Take care, too, when buying bread. Many bakers try to give the impression that their products are good sources of fiber by using words like “organic” or “wheat bread” on their labels, or by adding coloring to the bread itself so that it resembles a whole grain loaf. Buyer beware. Most of these products list unbleached white flour as their first ingredient, and fail to provide much fiber. Real whole-grain breads list whole wheat or whole rye flour as their first ingredient.
You should also increase your consumption of fruits, vegetables, peas, beans, and nuts, all of which supply fiber. Try eating a raw or cooked cruciferous vegetable (cabbage, cauliflower, brussels sprouts) two or three times a week, as well.
Fiber: There's More to the Story Than BranMost substances in food are digested before they leave the small intestine. The parts that continue through the large intestine undigested are fiber—what earlier generations called roughage.Once it became clear that eating fiber could apparently help prevent cancers of the colon and breast, cereal companies seized the opportunity to promote their products' cancer-fighting properties. As a result, consumers began to believe that only bran cereals and grains contain fiber. If the Cauliflower Council had had millions to spend on advertising, the public impression of fiber might have been different.Actually, fiber is present to some degree in a huge variety of plant products. There are two major types, and both can help prevent cancer.Soluble fiber is found in legumes (peas, peanuts, lentils, and beans, for example), barley, oats, and fruits. Beans and oat bran work particularly well in clearing out the digestive system.Insoluble (non-dissolving) fiber, which passes through the gastrointestinal tract in more or less its original form, is particularly effective against colon cancer. Excellent sources include vegetables, whole grains, baked goods made with whole wheat, and especially wheat bran.What's required, as always, is to eat a smorgasbord of produce: not only bran but also whole vegetables, to be sure of gaining all the beneficial compounds waiting inside the fiber. |
One of the reasons many vegetables seem to prevent colorectal cancer may lie in the rich amount of folic acid they contain. Population surveys have found that the disease is less frequent among people who have a high amount of this vitamin in their diets, and there’s evidence that taking folic acid supplements can reduce the risk even further.
In the recent Nurses’ Health Study, women taking more than 400 micrograms of the vitamin daily (usually in the form of a multivitamin supplement) enjoyed a 75 percent reduction in their risk of colorectal cancer. It’s important to remember, though, that the protective effects of the folic acid pills weren’t noticed until the women had been taking them for more than 15 years—a fact that emphasizes the importance of starting prevention at an early age and sticking with it for a lifetime.
Calcium, in the form of low-fat or nonfat dairy products or in fish with soft, edible bones, such as salmon and sardines, provides another hedge against colon cancer. Calcium is important because it allows the cells that line the colon to reproduce normally. Without enough calcium, the same cells multiply abnormally. Calcium inhibits malignant processes in the bowel in another way, too. When calcium meets with food-derived fats that have reached the bowel, the two materials combine, creating a harmless substance. Be sure to get at least the Recommended Daily Allowance of 1,000 milligrams calcium in a combination of food and pill form every day.
Another strong risk factor for colon cancer is the presence of polyps in the large bowel. These small growths on the inner walls, visible through a colonoscope, can turn cancerous over time. If you have polyps, you should try to stick to a low-fat, high-fiber, high-antioxidant diet. Even late in life, modifying your diet can help prevent polyps from becoming cancerous.
One other risk factor that should be noted is alcohol. Heavy drinking may double or triple the risk of colorectal cancer. The higher your risk, based on other factors, the less alcohol you should drink.
Lung Cancer
Lung cancer is a major killer of men and women alike. In fact, it now causes more deaths in American women than breast cancer, partly because breast cancer is being identified early and because treatments for it have grown more successful.
Over and over again, smoking has been shown to be the greatest risk factor for developing lung cancer, though air pollution might also have a role. The surest way for a smoker to cut the risk is to quit. Failing that, however, the next best move is to get plenty of the antioxidant vitamins that are thought to provide some degree of protection to both smokers and nonsmokers. Vitamin A, vitamin C, vitamin E, vitamin B12, folic acid, and selenium are the antioxidants to emphasize. Supplements of beta-carotene are more controversial.
While several population surveys have suggested that a diet rich in the fruits and vegetables that contain beta-carotene reduce the risk of lung cancer, taking the vitamin in supplement form may actually increase the threat of the disease. In one major study, when smokers were given 20 milligrams of beta-carotene daily, their odds of lung cancer inched slightly higher. And the more a person smoked, the greater were the supplement’s cancer-promoting effects.
Good food choices to discourage lung cancer include very dark green leafy vegetables (spinach, broccoli, kale), dark orange and yellow fruits (apricots, oranges, cantaloupes) and vegetables (pumpkin, squash, sweet potatoes, carrots), other citrus fruits (grapefruit, limes), soybeans and foods made from them (but not soy sauce), dried beans, tomatoes, and low-fat dairy products. The longer you have smoked, the more fruits and vegetables you need to even begin to offset the cancerous effects on your lungs. Supplements can also help, though not in megadoses that can easily become toxic. Check with your doctor before radically increasing your intake of antioxidant vitamins.
Stomach Cancer
Over the years, scientists have discovered a number of links between diet and stomach cancer. The most notorious dietary culprit is salt. Researchers say that there is a direct connection between stomach cancer and eating a large amount of salty, pickled, or smoked foods (such as smoked meats) as well as foods preserved with salt. The salt irritates the cells in the stomach lining, causing them to reproduce more rapidly than they normally would; salt may also make cancer-causing chemicals even stronger.
It seems that the incidence of stomach cancer in the U.S. dropped as canning and freezing replaced salt-based preservation as the preferred way of keeping food. Unfortunately, the processed foods we’ve adopted more recently contain so much salt that it once again presents a problem. The risk is heightened by eating too much vitamin-poor junk food and too little fruit and vegetables. Smoking has also been implicated in stomach cancer.
Dietary best bets to help prevent stomach cancer include lots of the following: citrus fruits and other foods containing vitamin C; liver, sweet potatoes, spinach, carrots, and other foods containing vitamin A; cabbage and other cruciferous vegetables; and onions. Those foods have been shown to reduce the risk of cancer by countering cancer-causing chemicals in the stomach, although the reasons aren’t clear.
Studies in Italy and China have strongly suggested that garlic is another shield against stomach cancer. A chief biostatistician at the National Cancer Institute says, “The weight of evidence is making it look like garlic really is protective against cancer.” One possible reason is that one or more chemical compounds in garlic prevent bacteria from growing in the stomach. Some of those bacteria, if left unchecked, convert food into cancer-causing compounds called nitrosamines.
Other Cancers
When cancer develops in the pancreas, treatment is extremely difficult. Prevention is therefore crucial.
Moderate to heavy smokers are two to four times more likely than nonsmokers to get pancreatic cancer. Don’t let your food smoke, either: Avoid red meat and cured pork products, such as ham, bacon, and cold cuts.
Eat plenty of fruits, vegetables, beans, peas, and nuts. Citrus fruits, tomatoes, carrots, and dried beans have reaped tremendous praise from researchers for warding off pancreatic cancer. Keep your alcohol intake low and your diet low in fat.
Prevention and Treatment: Same Menu?Nutritional recommendations for cancer prevention and cancer treatment often go hand in hand because they are based on the same clinical findings. "Prevention is just treatment, early," said Daniel Nixon, M.D., director of Cancer Prevention and Control at the Medical University of South Carolina, Charleston. Dietary patterns that promote tumor growth should simply be reversed: If fat intake encourages cancer, for example, then cutting down on fat should "starve" it.Other experts disagree. They suggest different diets altogether for cancer patients—more fat, for example, to "build them up."One close observer of the debate is Michael Lerner, president of Commonweal, a health and environmental research institute in Bolinas, California. Lerner, who has studied both mainstream and unconventional views of cancer, has served as a special consultant to the federal Office of Technology Assessment for a congressional study of complementary cancer therapies. In his book Choices in Healing: Integrating the Best of Conventional and Complementary Approaches to Cancer, Lerner summarizes the major overlapping recommendations of experts in traditional and nontraditional cancer therapies:
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The Oral Cavity, Larynx, and Esophagus
The oral cavity includes the lips, the insides of the cheeks, the gums, the soft palate, the tonsils, and floor of the mouth, and the tongue. The larynx, or voice box, lies just above the windpipe (trachea). The esophagus is the tube leading from the mouth down to the stomach. Esophageal cancer is rare but often fatal when it strikes.
Drinking alcohol and smoking both increase the risk of oral, laryngeal, and esophageal cancers. The two habits together multiply the influence that each has separately. If you chain smoke and drink heavily you are many times more likely than a nonsmoker to develop oral and throat cancers.
Deficiencies in vitamin A and the B-complex vitamins, more common among heavy drinkers than among nondrinkers, have been associated with oral cancers. Vitamin C helps protect the cells that line the mouth, larynx, and esophagus against cancer. Eating a balanced diet full of vitamins and minerals while avoiding smoking and drinking is the best known nutritional way to keep these delicate tissues healthy.
The Liver
Cancer of the liver has been linked with cirrhosis, a chronic liver disease in which normal tissue is replaced by fibrous tissue, leading to a loss of function. Cirrhosis is a common result of heavy alcohol consumption. One contributing factor may be the additives used in processing alcohol. Another is that people who drink heavily tend to have poor appetites. They don’t eat very well and can develop nutritional deficiencies that weaken the liver and many parts of the immune system.
Taking Stock
According to Dr. John Potter, director of the Fred Hutchinson Cancer Center in Seattle, the best evidence available today indicates that vegetables and fruits are the nutritional stars in prevention of most major types of cancer. What benefits most, he says, are the epithelial (surface) cells that line many parts of the body: the lung, bladder, cervix, mouth, larynx, throat, esophagus, stomach, pancreas, colon, and rectum. Ongoing studies are expected to highlight some of those effects more definitively.
Some types of cancer were not included in this overview because scientific findings are too limited to justify making any claims. Nevertheless, research into dietary culprits in endometrial and cervical cancer, skin cancer, and others is well underway, and could turn up some life-saving information in the coming years.
While studies continue, the best way to prevent cancer is to eat a variety of foods, never concentrating too much on any one kind. Even the noble broccoli, he points out, contains substances that have stimulated the growth of tumors in laboratory experiments. If you restrict your diet to a single small group of foods you will run the risk of missing out on important, perhaps still unknown, anti-cancer elements found only in others.