Prevention of Cancer - Cancer

Prevention of Cancer

Preventing cancer depends on avoiding the risk factors linked with cancer and maintaining a healthy immune system that efficiently eliminates abnormal cells from the body. This can be accomplished in a number of ways, including adopting a diet that ensures the optimal intake of immuno-enhancing nutrients and decreasing the intake of immuno-suppressing foods which weaken the immune system. Living a life free from continual emotional or mental stress is also important, as is avoiding carcinogenic toxins in the home and in the environment.

Nutritional Therapies.     Cancer rates differ noticeably in various parts of the world depending on dietary patterns, which suggests that diet plays a major role in cancer. Diets containing foods high in carbohydrates and cholesterol are now considered risk factors for cancer, while diets high in vitamin E, vitamin C, betacarotene, fiber, and other substances may prevent certain cancers. A five-nation study of 802 patients with pancreatic cancer, reported by G. Howe in the May 1992 issue of International Journal of Cancer , for example, showed that cancer was directly related to intake of carbohydrates and cholesterol and inversely related to dietary fiber and vitamin C.

The Role of Fiber in Preventing Cancer.     In The Cancer Eating Recovering Plan , Dr. Daniel Nixon cites an impressive number of studies suggesting that fiber can reduce the risk of cancer. Water-insoluble fiber has been associated with decreased cellular activity and decreased polyp formation in the gut, and thereby is thought to help prevent colon cancer. Fiber also acts as a laxative and reduces the amount of time food remains in the intestinal tract. It may also bind with carcinogens in the gut and render them harmless. A final benefit is that fiber may alter gut bacteria and acidity so that fewer carcinogens are produced. The water-soluble group (gums, pectin, and others) also tend to lower cholesterol levels in the blood, which may reduce the risk of some cancers. Nixon stresses that Americans should consume as much as 35 grams of fiber daily to prevent cancer.

Charles Simone writes in Cancer & Nutrition that many cancer specialists have found that fiber protects against colon/rectal cancer, breast cancer, heart disease, diverticular disease, obesity, and diabetes. A low incidence of cancer is seen in people who consume large amounts of carotene-rich foods and cruciferous vegetables such as cabbage, broccoli, cauliflower, and brussels sprouts. Fiber's protective action, Simone explains, is due to the fact that it binds bile acids, cholesterol, lipids poisons, and carcinogens. It also increase the weight and mass of stool, which dilutes carcinogens. Additionally, it decreases the gastrointestinal transit time so that the carcinogens are excreted more quickly. It also helps keep the intestinal flora healthy. Finally, high fiber intake may reduce the risk of breast cancer by lowering estrogen levels and changing the way food is absorbed in the gut.

Simone especially recommends high-fiber cereals and vegetables of the Brassiceae family which provide fiber and induce enzymes to destroy certain carcinogens. Dieters are advised to eat whole or lightly milled grains such as rice, barley, and buckwheat. Whole wheat bread and wheat pasta, cereals, crackers, and other grain products should also be eaten.

Carbohydrates.     According to Nixon, cross-national studies have shown that high intake of carbohydrate-rich foods, especially vegetables and fruits, has a cancer-fighting effect. These foods tend to be high in vitamin and chemopreventive compounds and fiber and low in fat–all of which may prevent cancer.

Fat.     Fat may act both as a promoter of cancer and as a modulator of the growth of existing cancers. Nixon presents a substantial amount of evidence that suggests that high-fat diets can cause breast and colon cancer. Conversely, he notes that a low-fat, low-calorie diet can inhibit the development of certain tumors and even slow the growth of established tumors in laboratory animals.

Scientists do not yet know which types of fat (saturated, unsaturated, omega-3 fatty acids, etc.) activate specific cancers. Therefore, Nixon recommends consuming less than 20% of calories as fat. For persons recovering from breast, colon, and prostate cancer, he emphasizes that 15% fat is even better. He also notes that most Americans consume fat that comes from animal products and that “animal fat is the major problem in our diets.”

Cholesterol.     A diet high in fats also increases blood cholesterol levels, although, according to Nixon, it is not clear precisely what role, if any, cholesterol might play in cancer. There is evidence, however, that farnesyl, a substance created as the liver synthesizes cholesterol, may have some role in the earliest stages of cancer development. Farnesyl may interact with oncogenes (the genes through which cancer begins) and create byproducts which trigger cancer cells to activate. If the farnesyl hypothesis is true, Nixon contends that consuming less cholesterol may reduce oncogene byproducts.

Protein.     According to Nixon, the link between excess protein consumption and cancer has not been definitively established. Nevertheless, he cites several population studies which found a relationship between high consumption of animal protein (meat and dairy products) and breast cancer. He also notes that laboratory studies have shown that when breast tumors are induced by carcinogens in animals, feeding the animals more protein leads to increased tumors. Some epidemiological studies have also linked animal protein intake to colon cancer, prostate cancer, and endometrial cancer. Nixon hypothesizes that one reason cancer causes cachexia is that it interferes with the body's ability to turn food into lean protein and muscle tissue.

Meat.     Nixon does not recommend a strict vegetarian diet because it lends itself to nutritional deficits; however, he does state that “limiting meat consumption to six ounces weekly has as much anticancer benefit as the total exclusion of meat from the diet.” He therefore advocates at least two meat-free days a week, a routine which helps reduce total fat intake and increase fiber intake.

Caffeine.     Simone notes that caffeine contains mutagens, or chemical compounds that cause heritable changes in the genetic material of cells. Some vegetables also contain mutagenic flavonoids, and mutagens are also produced in charred and smoked foods. Mutagens can also be produced at lower temperatures, such as from the normal cooking of meat. Others, like coffee and horseradish, contain quinones and allyl isothiocyanate, although the risk of developing cancer from mutagens in humans appears minimal.

Food Carcinogens.     University of California Berkeley researcher Bruce Ames has found that some plants have certain molecules to protect them from microorganisms and insects–some of which are carcinogenic or mutagenic in humans. For example, black pepper contains piperine and sarole; bruised celery contains psoralen; herbal teas contain pyrolizidine; and mushrooms contain hydrazines. Foods that pose the greatest risk of cancer in humans, according to Simone, are the mycotoxins (aflatoxin) and nitrous compounds from bacteria.

Food Additives.     Simone warns that there are now more than 3,000 intentional food additives, some of which are potentially carcinogenic. One of these, nitrite, for example, is sometimes converted in the body to nitrosamine, a potent carcinogen. In addition, more than 12,000 unintentional additives are found in packaging and food processing, including vinyl chloride and diethylsilbestrol, which may cause some cancers.

Obesity and Cancer.     Simone also notes the increasing evidence that excess weight and obesity are directly linked to cancer. According to Simone, obesity is a major risk factor for the development of endometrial cancer (cancer of the inner lining of the uterus) in postmenopausal women. The reason, he suggests, is because obese postmenopausal women produce substantially more of the female hormone estrone. This increased production is directly related to the number and size of the woman's fat cells, since estrone is manufactured in fat cells from another hormone called androstenedione. Estrone apparently stimulates the uterus, and this is believed to cause endometrial cancer.

Similarly, postmenopausal women who take estrogens daily for symptoms of menopause also have a higher incidence of endometrial cancer. Simone also notes that obese persons also usually consume more fats in their diet, and this, as noted, is a major risk factor for breast and colon cancer.

Phytoestrogens.     According to Alternative Medicine: What Works Chinese and Japanese women who eat traditional foods have lower breast cancer rates than Western women, a fact that leads some researchers to speculate that the predominantly vegetarian Asian diet may lower the risk of cancer and heart disease. Asians eat less fat and protein, and more carbohydrates than Westerns, and a low-fat diet is known to protect against several cancers.

Both Chinese and Japanese women, for example, consume tofu, green soybeans, and other soy products, which contain phytoestrogens (estrogen-like compounds found in plants). Consequently, the level of phytoestrogens they excrete is quite high. One study of Chinese women in Singapore reviewed by Adriane Fugh-Berman found that the intake of soy products appeared to protect premenopausal (but not postmenopausal) women from breast cancer.

Vitamin and Mineral Therapies.     Chapters 2 and 3 detail a number of clinical trials proving that vitamins and minerals have a protective effect against cancer. These include betacarotene, vitamin A, vitamin C, vitamin E, selenium, and zinc.

Vitamins A, C, and E may also help remove potentially harmful oxidative compounds from cells capable of damaging DNA, thus causing cancer. These vitamins are called “anti-oxidants” because they inhibit the harmful activity of free radicals and prevent oxidative damage. The extent of their ability to prevent cancer is still not fully known. Some vitamins and vitamin precursors such as beta-carotene appear to hinder the development of skin cancer and upper digestive tract cancers, as well as cervical cancer in its earliest stages.

Vitamin A and Cervical Dysplasia.      Alternative Medicine: What Works suggests that vitamin A supplements may lower the risk of cervical dysplasia. In a controlled study of 301 women with a precancerous condition, cervical dysplasia, derivatives of vitamin A called retinoids were applied to the cervix (the neck of the uterus). This treatment completely reversed the dysplasia in 43% of women, compared to 27% of those who used placebo cream. However, in the case of severe dysplasia, there was no difference between placebo and retinoids.

Vitamin A and Skin Cancer.     Vitamin A derivations have been shown to be effective in precancerous conditions of the skin, mouth, and vocal cords, according to Alternative Medicine: What Works. They can also normalize some cells effected by leukemia.

Vitamin A and Breast Cancer.      Alternative Medicine: What Works states that vitamin A may also help prevent breast cancer. In a study of the diets of 89,494 nurses, those who ingested the most vitamin A had 16% less risk of breast cancer. When vitamin A supplements were given to those needing it most, their risk also went down.

Folic Acid and Colon Cancer.     Folic acid, a B vitamin, may be one of the key ingredients in fruits and vegetables that prevent colon cancer. Elyse Tanouye reports a study conducted by the Harvard Medical School in the June 2, 1993 issue of the Wall Street Journal which found that folic acid appears to turn cancer genes off. Analyzing information obtained from questionnaires on patient's diets during a one-year period, Dr. Edward Giovannucci and colleagues at the Harvard Medical School found that a high intake of folic acid–from fresh fruits and vegetables and vitamin supplements–was associated with a lower risk of developing tumors. In addition, people drinking the equivalent of two alcoholic drinks a day were at an 85% higher risk of developing tumors than nondrinkers. Giovannucci hypothesized that folic acid helps transfer a compound called methyl from molecules commonly found in the body to other molecules that turn off cancer genes. When the process, called methylation, doesn't work–as, for example, when alcohol is introduced–cancer genes produce protein that appear to cause the cells to proliferate. Others researchers, including Dr. Joel Mason at Tufts University, have shown that folate contributes to normal tissue formation by guarding the integrity of the genetic messages encoded in DNA.

Dr. Gladys Block, professor at the University of California, Berkeley School of Public Health, suggested that the study indicates that many people need to take daily folic acid supplements and fortified prepared foods with folic acid to prevent cancer. Most American do not eat balanced diets, she noted, and may be deficient in folic acid.

Calcium.     Nixon cites research suggesting a possible link between calcium deficiencies and cancer. Epidemiological studies, for example, have shown that the more milk a person drinks, the lower their risk of colon cancer. Calcium has also been shown in laboratory studies to decrease the cell division activity in the colon lining walls. Calcium may also bind and inactivate carcinogens in the stool. Excellent sources of calcium along with nonfat dairy products include asparagus, broccoli, Great Northern and navy beans, okra, spinach, and soybean products (tofu).

Botanical Medicine Therapies.     Several botanical nutrients discussed in Chapter 5 have been shown to be effective preventive agents against cancer, including spirulina, aloe vera, green tea made from the leaves of Camellia sinensis , echinacea, garlic, mistletoe, shiitake mushrooms (extract of Lentinus edodes ), and maitake mushrooms.