From: wheeler@super.org (Ferrell S. Wheeler)
Subject: Re: Vegetarian diets and cancer [was vegetarianism & nutrition]
Organization: Supercomputing Research Center (Bowie, MD)
Date: Wed, 9 Sep 1992 19:19:48 GMT


 FOODS FOR CANCER PREVENTION

     Of the many diseases that affect people these days, cancer is among the
most feared. But despite a wealth of scientific data, most people remain
unaware of how they can reduce their risk of developing cancer. According
to the National Cancer Institute, as much as 80 percent of all cancers are
due to identified factors, and thus are potentially preventable. Thirty
percent are due to tobacco use, and as much as 35 to 50 percent are due to
foods. It is easy to control these and other risk factors.

* What is Cancer?
     Cancer begins as a single abnormal cell that begins to multiply out of
control. Groups of such cells form tumors and invade healthy tissue, often
spreading to other parts of the body. Carcinogens are substances that
promote the development of cancerous cells. They may come from foods, from
the air, or even from within the body. Most carcinogens are neutralized
before damage can occur, but sometimes they attack the cell's genetic
material (DNA) and alter it. It takes years for a noticeable tumor to
develop. During this time, compounds known as inhibitors can keep the cells
from growing. Some vitamins in plant foods are known to be inhibitors.
Dietary fat, on the other hand, is known to be a promoter that helps the
abnormal cells to grow quickly.

* Fiber Fights Cancer
     In 1970, British physician, Denis Burkitt, observed that a high-fiber diet
reduces diseases of the digestive tract. He observed that in countries where
diets are high in fiber (that is, plant-based diets), there were fewer cases
of colon cancer. Around the world, this has proven true. The highest fiber
intakes are found in non-industrialized nations where meat is scarce and
plant foods fill the menu. Animal products contain no fiber. The United
States and other Western nations whose diets are based upon animal products
have the highest rates of colon cancer.
     While no one is certain exactly how fiber protects against digestive tract
disorders, there are several possibilities. By definition, fiber cannot be
digested by humans early in the digestive process. It moves food more
quickly through the intestines, helping to eliminate carcinogens. It also
draws water into the digestive tract. The water and fiber make fecal matter
bulkier, so carcinogens are diluted.
     Bile acids are secreted into the intestine to help digest fat; there,
bacteria can change the acids into chemicals which promote colon cancer.
Fiber may bind with these bile acids and evict them from the intestines.1
Also bacteria in the colon ferment the fiber creating a more acidic
environment which may make bile acids less toxic.
     Fiber is also protective against other forms of cancer. Studies have shown
that stomach cancer and breast cancer are less common on high-fiber diets.2,3
Fiber affects levels of estrogens in the body. Estrogens are normally
secreted into the intestine, where fiber binds with the hormone and moves
it out of the body.4 Without adequate fiber, the estrogen can be reabsorbed
from the intestine into the blood stream. High levels of estrogen are linked
to a higher risk of breast cancer.
     In the US, the average daily fiber intake is 10 to 20 grams per day.
Experts recommend 30 to 40 grams per day. The best sources of fiber are
whole grains, beans, peas, lentils, vegetables, and fruits. Foods that are
closest to their natural state, unrefined and unpeeled, are highest in
fiber.

* Fat Raises Cancer Risks
     Cross-cultural studies have revealed that the populations with the highest
levels of fat consumption are also the ones with the highest death rates
from breast and colon cancer. The lowest rates are in groups with the lowest
consumption of fats.5 Migration studies help to rule out the influence of
genetics.6
     Fat clearly increases one's risk for cancer, and it may also adversely
affect breast cancer survival rates for those who have cancer.7
     Although the total amount of fat one eats is of concern, there is evidence
that animal fat is much more harmful than vegetable fat. One study noted a
200 percent increase in breast cancer among those who consume beef or pork
five to six times per week. Dr. Sheila Bingham, a prominent cancer
researcher from the University of Cambridge, notes that meat is more closely
associated with colon cancer than any other factor.8 Meat and milk are also
linked to both prostate and ovarian cancers.9

* How Fat Affects Cancer Risks
     Fat has many effects within the body. It increases hormone production and
thus raises breast cancer risks. It also stimulates the production of bile
acids which have been linked to colon cancer. 
     The average diet in the US is about 37 percent fat. The National Cancer
Institute suggests that people lower that percentage down to 30 percent;
however, studies have shown that fat intake should be well below 30 percent
to have an anti-cancer affect. Ten to fifteen percent is more likely to be
helpful.

* The Importance of Vegetables
     Not only are vegetables low in fat and high of fiber, they also contain
many cancer-fighting substances. Carotenoids, the pigment that gives fruits
and vegetables their dark colors, have been shown to help prevent cancer.
Beta-carotene, present in dark green and yellow vegetables, helps protect
against lung cancer and may help prevent cancers of the bladder, mouth,
larynx, esophagus, breast, and other sites.
     Vegetables such as cabbage, broccoli, kale, turnips, cauliflower, and
Brussels sprouts contain flavones and indoles which are thought to have
anti-cancer activities.
     Vitamin C, found in citrus fruits and many vegetables, may lower risks for
cancers of the esophagus and stomach. Vitamin C acts as an antioxidant,
neutralizing cancer-causing chemicals that form in the body. It also blocks
the conversion of nitrates to cancer-causing nitrosamines in the stomach.
     Selenium is found in whole grains and has the same antioxidant effects as
vitamin C and beta-carotene. Vitamin E also has this effect. Caution is
advised in supplementing selenium, which is toxic in large doses.

* Alcohol
     Excessive intake of alcohol raises one's risks for cancers of the breast,
mouth, pharynx, and esophagus. When combined with smoking, these risks
skyrocket. It also raises risks for stomach, liver, and colon cancer.10

* Vegetarians are Better Off
     All of the evidence points to a low-fat, high-fiber diet, that includes
a variety of fruits, vegetables, whole grains, and beans, as being the best
for cancer prevention. Not surprisingly, vegetarians, whose diets easily
meet these requirements, are at the lowest risk for cancer. Vegetarians have
about half the cancer risk of meat-eaters.11 
     Vegetarians have higher blood levels of beta-carotene. They consume more
vitamin C, beta-carotene, indoles, and fiber than meat-eaters. Vegetarians
also have stronger immune systems. German researchers recently discovered
that vegetarians have more than twice the natural killer cell activity of
meat-eaters.12 Natural killer cells are specialized white blood cells that
attack and neutralize cancer cells. Also, vegetarians tend to eat more soy
products than meat-eaters. Soybeans contain many substances that are
anticarcinogens, including lignans and phytoestrogens. A diet that is rich
in soybeans may be one reason for the lower incidence of breast cancer in
Asia.

* Conclusion
     A cancer-prevention diet is one that is high in fiber, low in fat
(especially animal fat), and includes generous portions of fruits and
vegetables. It also minimizes or excludes alcohol. The best diets are pure
vegetarian diets.

References:
1. Kritchevsky D. Diet, nutrition, and cancer: the role of fiber. Cancer
1986;58:1830-1836.
2. Risch HA, et al. Dietary factors and the incidence of cancer of the
stomach. Am J Epidemiol 1985;122:947-959.
3. Lubin F, et al. Role of fat, animal protein and dietary fiber in breast
cancer etiology: a case control study. J Natl Cancer Inst 1986;77:605-612.
4. Goldin BR, et al. Estrogen excretion patterns and plasma levels in
vegetarian and omnivorous women. N Engl J Med 1982;307:1542-1547.
5. Lane HW, Carpenter JT. Breast cancer: incidence, nutritional concerns,
and treatment approaches. J Am Diet Assoc 1987;87:765-769.
6. Minowa M, et al. Dietary fiber intake in Japan. Human Nutr Appl Nutr
1983;37A:113-119.
7. Wynder EL, et al. Diet and breast cancer in causation and therapy. Cancer
1986;58:1804-1813.
8. Bingham SA. Meat, starch, and non-starch polysaccharides and bowel
cancer. Am J Clin Nutr 1988;48:762-767.
9. Rose DP, et al. International comparisons of mortality rates for cancer
of the breast, ovary, prostate, and colon, and per capita food consumption.
Cancer 1986;58:2363-2371.
10. Breslow NE and Enstrom JE. Geographic correlations between cancer
mortality rates and alcohol-tobacco consumption in the United States.
J Natl Cancer Inst 1974;53:631-639.
11. Phillips RL. Role of lifestyle and dietary habits in risk of cancer
among Seventh-Day Adventists. Cancer Res (Suppl) 1975;35:3513-3522.
12. Malter M. Natural killer cells, vitamins, and other blood components of
vegetarian and omnivorous men. Nutr and Cancer 1989;12:271-278.

Physicians Committee for Responsible Medicine
P.O. Box 6322
Washington, DC 20015
(202) 686-2210
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