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Colon Polyps and Colon Cancer
The End Result of Daily Dietary Abuse

By Dr. John McDougall

In the Western world, colon cancer (also known as colorectal cancer) is the second most deadly cancer.   Each year in the United States and Europe 130,000 to 180,000 new cases are diagnosed.   Slightly more men than women develop colon cancer.  A person older than 50 years has about a 5% chance of developing colon cancer and a 2.5% chance of dying of the disease.  Unfortunately, because the treatments are so ineffective, after 5 years only about 40% of people diagnosed are still alive.  This is a disease primarily of people consuming a diet high in meats (including poultry and fish, dairy products, and fats; and low in fruits and vegetables.  Colon cancer arises from polyps (also called adenomas).

In autopsy studies, approximately 35% of people eating the western diet are found to have polyps.1 Polyp formation is the consequence of chronic irritation of mucous membrane tissues – just like callus forms on the palm of your hand from the irritation caused by the abrasion of hard physical work.   In the case of your skin (epidermal issue), the body’s response is the formation of layers of protective keratin – the callus.  The mucous membranes found in the intestine, sinus cavities, and the female cervix respond to chronic irritation by cell growth (proliferation) causing a protective mound of tissue to form, which when large and distinct is called a polyp.

The obvious source of that irritation in the colon is the contents of the intestine, the remnants of the partially digested foods – and the longer and stronger the irritation, the greater the body’s response, and the larger the polyp.   During cell division is the time when our genetic materials – our strands of DNA – are exposed to the effects of cancer-causing substances.  Therefore, the sequence to serious disease is as follows: irritation,  cell proliferation, polyp development, and finally, cancer.   Large polyps, which are further along this developmental sequence, are more likely to be cancerous -- polyps less than 5mm (1/2 inch) are not likely to be cancer; at 10 mm, 1% are; and at 20 mm, 17% show cancerous changes.

The key to preventing polyp formation, slowing their growth, preventing their transition to cancer, and possibly, slowing the growth of the cancer even after it is started, is to stop the irritation of the mucosa of the intestine.  In other words, your goal is to bathe the walls of your intestine with foodstuffs as soft and gentle as fluffy mashed potatoes.

Transition time from the earliest changes in the mucous membranes to the beginning of actual cancer takes on average 10 to 15 years.2   Fewer than one in 20 small polyps (adenomas) will grow larger and transform into cancer.  Once the cancer begins, the time for spread of the cancer to other parts of the body (metastasis), and obvious disease, and finally death, takes another 10 to 20 years.  Therefore, the whole process from normal cells to cancer and death will span on average 20 to 35 years.  This is one reason colon cancer is primarily a disease of older people.

Who gets colon cancer?

About 75% of people diagnosed with colon cancer have no predisposing characteristics other than they eat the rich Western diet.  The other 25% have conditions that put them at higher than average risk.  These people have inflammatory bowel disease (1%) (discussed in the November 2002 McDougall newsletter), familial adenomatous polyposis (1%), and hereditary nonpolyposis colorectal cancer (5%).  The remaining high risk people are those with a family history of colon cancer (15 to 20%).  People with one or two first-degree relatives (parents, brothers, sisters) with colon cancer have twice the general risk of developing colon cancer.  The question that has not been fully answered is, is this due to heredity passed on by genetics or the fact that mother and father teach sons and daughters which foods to like and how to cook?  The learning-family-relationship emphasizes again that the most important factor in polyp disease and colon cancer is the contents of the colon – determined by the foods we eat.  Diet influences all stages of the development of colon cancer from the beginnings of cell proliferation, to polyp formation, to the final stages of cancer.

Diet Is the Irritant:

In 1971 Dr. Dennis Burkitt observed that African blacks consuming high-fiber and low-fat, low-animal-product foods had a lower rate of death from colon cancer, than did African whites on a low-fiber, high-fat diet.3   From this he hypothesized that diet was the cause of cancer of the polyps and colon cancer.   Further evidence on the causal relationship of diet and cancer was made by researchers who noticed a 50-fold variation in the incidence of this disease worldwide.4   In countries where people eat rich diets – high meat, dairy, fats, sugars, and processed foods – there were high rates of polyps and colon cancer.  Conversely, a high intake of starches, fruits and vegetables was associated with a low risk of these colon problems.  When people move from a county of low incidence (say a rural African country) to a country of high incidence (the USA) they acquire the risk for polyps and colon cancer of their new country.

In animal experiments low-fat diets have been found to protect against these diseases.5 Both meat and vegetable fats seem to increase the risk of polyps and cancer. Hydrogenated fats, found in shortenings and margarines and many kinds of prepared and packaged foods, may be especially cancer-promoting.6 Even though all the intricate details have not been worked out, the guilty finger clearly points to the meat and fat, and the lack of fruits, vegetables and dietary fiber.

There have been many mechanisms proposed for the effects of diet on cancer development.  For example, a high-fat diet may increase the production of bile acids from the liver.  Dietary fiber will combine with and deactivate these bile acids.  In the colon, bile acids are converted into cancer-causing substances by bowel bacteria.  The kinds of bacteria that grow in the intestine depend upon the food that is provided them – in other words the foods that we have eaten.  On a rich diet, “unfriendly” bacteria that make cancer-causing substances grow in the colon.  These colon bacteria play several roles: they enhance the effects of bile acids, and increase the production of cancer-causing substances and tumor promoters.

The Role of Dietary Fiber:

Fiber is the non-digestible carbohydrates found in foods.  Plant foods contain fiber – no animal food does.  Refining of plant foods removes fiber.  Fibers act by diluting and combining with cancer promoters thus reducing their access to the colon and the rest of our body.7    Fiber is also fermented into butyric acid, which inhibits the growth of cancer cells.  There are two general classes of fiber: soluble and insoluble. Wheat bran, which is classified as an insoluble fiber, appears to be the most effective at preventing colon disease, whereas soluble fibers, such as guar gum, pectin and oat bran are less effective.  Increasing dietary fiber will not only protect us from diseases of the colon, but fiber has also been shown to decrease cholesterol, improve insulin resistance, reduce blood pressure and prevent heart disease.8

The Australian Polyp Prevention Project found that a low-fat diet supplemented with wheat bran reduced the risk of recurrence rate of large polyps (adenomas).9 One estimate suggests that if we were to increase our daily fiber intake by 13 grams, the risk of colon cancer would decrease by 31% (50,000 cases prevented in the USA annually).10 The average American consumes between 8 and 14 grams of fiber a day – all they manage to get from fiber-free animal products and refined grains.  People on the McDougall diet, like the diet of people in rural Africa, consume 40 to 100 grams a day.

The Role of Meats:

Recent evidence from Africans also suggests that fiber may play a smaller role than the animal product consumption.  As the modern African diet changes to more refined foods with less fiber, the incidence of colon cancer and polyps still remains low, probably because their diet is still very high in carbohydrates, and low in fat and animal foods.11  Animal fat, cholesterol and protein have all been shown to have cancer-promoting properties in animal experiments.   Even chicken and fish have been found to be associated with high rates of colon cancer.12  The sulfur-containing amino acids, found in high concentration in red meat, poultry, and fish, produce a large amount of very noxious hydrogen sulfite, which has been shown to impair cellular metabolism and mucous production.

Friendly Bacteria – Probiotics:

The bacteria living in the intestine, known as the intestinal microflora, perform vital functions for the health of the intestine and the whole body.  The addition of the right kinds of bacteria, referred to as “friendly” bacteria, to the diets of experimental animals has been shown to reduce their risk of developing colon cancer.13 These bacteria may provide their benefits by deactivating cancer-causing chemicals in the colon and by replacing “unfriendly” bacteria that produce cancer-causing substances.  The kinds of bacteria that grow in your intestine depend upon the diet you eat.  Meat, including poultry and fish, and dairy products will encourage the growth of “unfriendly” bacteria.  If you eat starches, vegetables and fruits then the bacteria will be of the “friendly” variety. You can also consume concentrated sources of friendly bacteria in the form of fermented foods and pills.

Fermented milk products, like yogurt, are often thought of as a great source of bacteria, like Lactobacillus, which is supposed to be healthy for the intestine and the whole body.  However, dairy products are unhealthy for many reasons (fat, cholesterol, proteins, infectious agents, chemical contamination, and allergy) and therefore, should not be your source of these bacteria.  In one study, increased intake of yogurt was found to be associated with an increased risk of having large precancerous polyps.14

The best way to get an added dose of “friendly” bacteria is to purchase them in the form of pills in your natural foods store – usually in the refrigerated section.  However, eating a healthy diet based on plant foods should be your primary effort to maintain a healthy intestinal microflora – give them the food and they will grow.

Screening for Polyps and Colon Cancer:

In 1995, the United States Preventative Services Task Force joined the American College of Physicians, the National Cancer Institute, the American Cancer Society, the World Health Organization, and the American Gastroenterological Association in recommending screening persons over the age of 50 years with an average risk for colon cancer.  Their recommendations are for fecal occult blood tests, sigmoidoscopy, or both.

Since 90% of cancer occurs after the ages of 55 years and the time required for transition from a normal colon to cancer is between 20 to 35 years15-17, an effective way to screen would be to do one exam between the age of 55 and 60.18-20 This would find most of the cancers already beginning as polyps. If no disease were present at this time, future examinations would be unlikely to benefit the person--since it takes so many years for a cancer to develop, and finally to kill. (Consider, that a person would be 80 to 90 years old to realize any benefit from exams performed after age 60 on someone with a normal colon before 60 years old.)

Digital Rectal Examination (DRE):  Like almost all physical examination procedures, DRE has not been tested in properly designed studies.  Since the disease will be at least 10 years old by the time its discovered, little benefit can be expected.

Occult Blood Test:  This is one of the most controversial areas of screening. Bleeding usually begins in the late stages of cancer, when cure is unlikely. For every 10 people who test positive for blood, one will be found to have cancer, four will have polyps and 5 will be normal.  These tests miss 20% to 50% of colon cancers and up to 80% of polyps.  Advocates of these tests claim screening may reduce the risk of death by 15 to 21% over 8 to 13 years.  But in actual numbers, 500 to 1,000 people may need to be tested annually for 10 years to prevent one death from colon cancer.21   Fecal occult blood screening is not innocuous – it can lead to anxiety, worry, loss of insurability, social stigma, injury from future tests and treatments, and sometimes death.22

Sigmoidoscopy Exams:  In one often-cited study, sigmoidoscopy examination once every 10 years reduced the risk of dying from colorectal cancer by 59%.23 More frequent screening gave no better results.

Colonoscopy:   Colonoscopy examination with a long flexible tube is most often recommended for evaluation of the colon and rectum.  Most gastroenterologists are convinced that this money-making procedure is much better24 than simpler, safer, cheaper tests; however, their enthusiasm should be taken with caution, because the results obtained in clinical trials may not apply to the general practice of medicine in your community.21 Despite its high diagnostic accuracy, colonoscopy should only be used for screening high-risk individuals. Studies support survival benefit for detection of precancerous polyps; but no survival benefit for detection of actual colorectal cancers. The National Polyp Study of more than 1,418 patients who had complete colonoscopy with one or more polyps removed, had an incidence of colon cancer 76% to 90% lower than expected.25 The same study showed that screening every three years proved as beneficial as annual screening.

My preferred alternative is a double-contrast barium enema and a flexible sigmoidoscope, which is much lower cost with fewer complications.26-28 Colonoscopy examinations, performed by experienced specialists, miss finding polyps 24 percent of time, and they are much more dangerous and costly than a barium enema and a sigmoid examination.29

If you should have a polyp found and removed, then an interval of at least three years is recommended before a follow-up examination is performed according to the recommendations of the National Polyp Study Workgroup, because only a small fraction of patients were found to have adenomas with advanced pathological features on follow-up.25

Diet May Help Even After Polyps and Cancer Begin:

Present day treatment of colon cancer – surgery, radiation, and/or chemotherapy – has done little to reduce a person’s risk of dying of this disease.  Furthermore, even after the removal new polyps grow back.  The reason they regrow is the cause of the disease has not stopped – the rich Western diet.  Therefore, one of the most important, and without a doubt, the most neglected recommendation for someone with polys or even colon cancer, is to stop “throwing gasoline on the fire” – change to a low-fat, unprocessed, plant-based diet.

Polyps have been shown to regress and disappear when the fecal material is diverted away from the colon by a surgical colostomy.30  This is because toxic irritation of the colonic tissues caused by the remnants of the Western diet is stopped – just like the callus in the palm of your hand will soften and disappear when you stop hard physical work.

Could a person who already has colon cancer benefit from a healthy diet?  It has never been tested. However, colon cancer sometimes seems to be cured without any intervention by the doctor – a medical mystery described as “spontaneous remission.”31  I have no doubt that a person is much more likely to have this miracle happen to them if in good, rather than poor, health.  Even if the disease does not completely disappear with a change in diet, there is substantial evidence that a healthy, low-fat, no cholesterol diet, such as I recommend, can slow the growth of cancer and allow the person to live longer, and without a doubt, in better health.  And besides, he won’t die constipated to his added misery.

10 Steps to a Disease-Free Colon:

1)  Center your diet on unrefined starches

2)  Add plenty of fruits and vegetables

3)  Avoid red meat, poultry and fish

4)  Avoid all kinds of added fats

5)  Add wheat bran, especially if you do not do 1-4 above

6)  Add “friendly” bacteria (probiotics), especially if you do not do 1-4 above

7)  Have one colon exam between 55-60 years

8)  Have large polyps removed when discovered

9)  Reverse the size of polyps by eating healthy

10) Survive cancer better with a healthy diet


1)  Midgley R. Colorectal cancer.  Lancet. 1999 Jan 30;353(9150):391-9.

2)  Winawer SJ.  Natural history of colorectal cancer.  Am J Med. 1999 Jan 25;106(1A):3S-6S;

3)  Burkitt D.  Epidemiology of cancer of the colon and rectum. Cancer. 1971 Jul;28(1):3-13.

4)  Maric R.  Meat intake, heterocyclic amines, and colon cancer.  Am J Gastroenterol. 2000 Dec;95(12):3683-4.

5)  Shike M.  Diet and lifestyle in the prevention of colorectal cancer: an overview.
Am J Med. 1999 Jan 25;106(1A):11S-15S

6)  Slattery ML.  Trans-fatty acids and colon cancer.  Nutr Cancer. 2001;39(2):170-5.

7)  Reddy BS.  Role of dietary fiber in colon cancer: an overview.  Am J Med. 1999 Jan 25;106(1A):16S-19S;

8)  Kim Y.  AGA technical review: impact of dietary fiber on colon cancer occurrence.
Gastroenterology. 2000 Jun;118(6):1235-57.

9)  MacLennan R.  Randomized trial of intake of fat, fiber, and beta carotene to prevent colorectal adenomas. The Australian Polyp Prevention Project.  J Natl Cancer Inst. 1995 Dec 6;87(23):1760-6.

10)  Howe GR.  Dietary intake of fiber and decreased risk of cancers of the colon and rectum: evidence from the combined analysis of 13 case-control studies. J Natl Cancer Inst. 1992 Dec 16;84(24):1887-96.

11)  O’Keefe S.  Rarity of colon cancer in Africans is associated with low animal product consumption, not fiber.  Am J Gastroenterol. 1999 May;94(5):1373-80.

12)  Singh PN.  Dietary risk factors for colon cancer in a low-risk population.
Am J Epidemiol. 1998 Oct 15;148(8):761-74.

13)  Wollowski I.  Protective role of probiotics and prebiotics in colon cancer.  Am J Clin Nutr. 2001 Feb;73(2 Suppl):451S-455S.

14)  Boutron M.  Calcium, phosphorus, vitamin D, dairy products and colorectal carcinogenesis: a French case--control study.  Br J Cancer. 1996 Jul;74(1):145-51.

15)  Bhattacharya I.  Screening colonoscopy:  the cost of common sense. Lancet 347:1744, 1996.

16)  Morson B.  Genesis of colonrectal cancer.  Clin Gastroenterol 5:505, 1976.

17)  Stryker S.  Natural history of untreated colonic polyps.  Gastroenterology 93:1009, 1987.

18)  Atkin W. Prevention of colonrectal cancer by once-only sigmoidoscopy. Lancet 341:736, 1993.

19)  Lieberman D.  Cost-effectiveness model for colon cancer screening. Gastroenterology 109:1781, 1995.

20)  Selby J. Screening sigmoidoscopy for colonrectal cancer.  Commentary.  Lancet 341:728, 1993.

21)  Pignone M.  Screening for colorectal cancer in adults at average risk: a summary of the evidence for the U.S. Preventive Services Task Force.  Ann Intern Med. 2002 Jul 16;137(2):132-41.

22)  Marshall K.  Population-based fecal occult blood screening for colon cancer: will the benefits outweigh the harm?  CMAJ. 2000 Sep 5;163(5):545-6;

23)  Selby J.  A case-control study of screening sigmoidoscopy and mortality from colorectal cancer.  N Engl J Med 326:653, 1992.

24)  Winawer SJ.  A comparison of colonoscopy and double-contrast barium enema for surveillance after polypectomy. National Polyp Study Work Group.  N Engl J Med. 2000 Jun 15;342(24):1766-72.

25)  Winawer SJ.  Randomized comparison of surveillance intervals after colonoscopic removal of newly diagnosed adenomatous polyps. The National Polyp Study Workgroup.
N Engl J Med. 1993 Apr 1;328(13):901-6.

26)  Chapman A. United States has recommended screening for colon cancer.  Why has barium enema been suggested?  BMJ 314:1624, 1997.

27)  Selby J.  A case-control study of screening sigmoidoscopy and mortality from colorectal cancer.  N Engl J Med 326:653, 1992.

28)  Dodd G.  The role of the barium enema in the detection of colonic neoplasms.  Cancer 70:1272, 1992.

29)  Rex D.  Colonoscopic miss rates of adenomas determined by back-to-back colonoscopies.  Gastroenterology 112:24, 1997.

30)  Feinberg SM. Spontaneous resolution of rectal polyps in patients with familial polyposis following abdominal colectomy and ileorectal anastomosis. Dis Colon Rectum  1988 Mar;31(3):169-75

31)  Serpick AA. Spontaneous regression of colon carcinoma. Natl Cancer Inst Monogr  1976 Nov;44:21

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The Meat Free Zone (MFZ) campaign is intended to make the MeatFreeZone logo as recognizable a symbol as the "Smoke Free Zone". The idea was originally conceived  when The WARM Store in Woodstock, NY, was in operation throughout the '90's (Woodstock Animal Rights Movement).  The store was truly a meat free zone as it was the first cruelty-free, Vegan, socially conscious animal rights store in the United States.  Now  that  the Vegan and Vegetarian movements have been growing so rapidly, more and more people are showing concern about the food in their diet and their overall  health and nutrition.  Many people are giving up eating fish, chicken, beef, pork (pigs ), dairy (milk, cheese, yogurt, ice cream) and eggs.  Headlines of Mad Cow disease, E-coli and salmonella are in the news with greater frequency.  Vegan and vegetarian recipe cookbooks are standard now  in all bookstores and many restaurants have added Vegan and Vegetarian options to their menus. We hope you will help us with the Meat Free Zone campaign by putting the signs up in your homes and workplaces and by spreading them to all the vegetarian and vegan restaurants that you know and frequent.  And someday we will have true "meat free zones" in establishments that serve meat.

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