Colorectal cancer is the third most common type of cancer in the world and the second leading cause of cancer deaths in North America. It targets the large intestine and the rectum. Cancer of the large intestine, called colon cancer, affects men and women equally, while rectal cancer is more common among men.
Cancer develops when the cells in the lining of the colon or rectum begin to grow out of control. These cells divide and multiply at abnormal rates, forming small clumps or growths known as polyps. When polyps first form, they are noncancerous (benign). Eventually some of the polyps can change to become cancerous (malignant). Polyps smaller than 1 centimeter (0.5 inch) rarely become malignant, but the cancer risk increases as the polyps grow in size. There's almost a 50 percent chance of cancer developing from polyps that are larger than 2 centimeters (1 inch). Several different types of polyps can grow in the intestine, but those called adenomatous polyps are most likely to cause cancer.
What causes colorectal cancer?
Scientists don't know what triggers polyps to develop. A hereditary factor may be involved. Studies indicate that people with a family history of colorectal cancer are much more likely to develop malignant growths in their intestinal tract.
Scientists also suspect that diet and lifestyle play important roles in the development of colorectal cancer. People at highest risk tend to eat more fat, red meat and refined carbohydrates. Studies indicate that people who exercise regularly and who eat high-fiber diets, with plenty of fruits and vegetables, have a lower risk of colon cancer.
Colorectal cancer develops very slowly, usually over a period of seven to ten years. By reacting quickly to certain warning signs, it is possible to prevent cancer from developing. There are also several screening tests that can detect the presence of polyps. Removing polyps is the best way to prevent colorectal cancer. Screening tests can also find cancer in the early stages, when treatment is more effective and a full recovery is still likely. Colorectal cancer often develops with no symptoms, which makes screening even more important.
There may be no symptoms in the early stages of colorectal cancer. See your doctor if you have any of these warning signs:
- a change in normal bowel habits for more than two weeks, such as constipation or diarrhea or both
- narrow, pencil-thin stools bright or dark red blood in or on your stools
- on more than one occasion constant abdominal pain or cramping
- frequent gas pain
- a feeling that your bowel doesn't empty completely
- weight loss for no apparent reason
- constant tiredness
Who’s at risk?
You are at risk for colorectal cancer if you are:
- over the age of 40; risk rises significantly at ages 50 to 55
- have a family history; risk is higher if the cancer affects more than one relative
- have an inflammatory bowel disease (ulcerative colitis, Crohn's disease)
- have a genetic disease such as Gardner's syndrome, familial polyposis or hereditary nonpolyposis colorectal cancer (HNPCC)
- are of Jewish or Eastern European ancestry
- are obese
- are sedentary
- smoke cigarettes
Preventing colorectal cancer with diet and nutrition
Dietary Fat. Diets high in total fat and saturated animal fat may increase the risk of colon and rectal cancer. Animal studies show that a high fat intake induces colon tumors, and studies in humans have linked a high fat intake with high rates of colon cancer.
A high-fat diet may increase the chances of colon and rectal cancer by increasing the amount of bile acids in the intestinal tract. After a meal, bile acids are released from the gallbladder to help break down fat. Despite their action as a digestive aid, bile acids also appear to enter colon cells and initiate cancer development.
To reduce your fat intake, choose lean meats, poultry breast and foods prepared with little or no added fat. Meat also seems to increase the risk of colorectal cancer. Many studies have found that higher intakes of meat increase the risk of the cancer. Cooking meat, poultry and fish at a high temperature forms heterocyclic amines, compounds found to be cancer-causing in laboratory studies. Cancer experts recommend consuming no more than 3 ounces (90 grams) of red meat per day (if eaten at all).
Omega-3 Fatty Acids. These special fats found in oily fish may reduce the risk of colon cancer by inhibiting normal cells from becoming cancerous. Fish oils may also inhibit the growth of cancerous cells. A few studies have found that fish oil supplements taken for up to six months actually improve the health of colon cells in people at high risk for colorectal cancer. While it is premature to recommend fish oil capsules for the prevention of colon and rectal cancer, it makes sense to add fish to your weekly menu. Aim to eat oily fish at least three times per week. Salmon, trout, herring, sardines and mackerel are good choices.
Carbohydrates: Sugar and Starch. High intakes of refined starches, especially foods made with white flour, seem to increase the risk of colorectal cancer. There is also evidence that sucrose-containing foods increase the risk. It's thought that refined starches and sugars increase the risk by elevating blood-glucose and insulin levels. Insulin, a hormone that clears glucose from the bloodstream, appears to be related to colorectal cancer.
As often as possible, avoid consuming too much table sugar, cookies, cakes, desserts, candy, chocolate, fruit drinks, soft drinks, syrup, corn syrup and jam. Refined foods such as white bread, crackers, presweetened breakfast cereals, cereal bars, granola bars, white pasta and white rice should be replaced with whole-grain products.
Dietary Fiber. It's long been thought that a diet high in fiber prevents colon and rectal cancer in a number of ways. An analysis of 13 studies of people with colorectal cancer concluded that an intake of fiber-rich foods is associated with a lower risk for the two cancers. However, two large studies revealed that when people at high risk for colon cancer (they have adenomatous polyps) were given a high-fiber diet or daily fiber supplements for a number of years, there was no reduction in the growth of polyps. The famous Nurses' Health Study also found no difference in the risk of colorectal cancer between women with the highest and lowest fiber intakes.
Whether fiber reduces the risk of developing colon cancer remains to be proven. It may be that high-fiber foods provide other anticancer compounds such as vitamins and antioxidants. However, because dietary fiber is associated with so many other health benefits, current recommendations are to consume 25 to 35 grams per day. See page 3, Chapter 1, for a list of fiber-rich foods.
Vegetables. Evidence that diets rich in vegetables protect from colorectal cancer is convincing. Many studies have found that many types of vegetables significantly reduce the risk of polyp recurrence and colorectal cancer. Raw vegetables, leafy green vegetables, cruciferous vegetables (broccoli, cauliflower, cabbage, turnip) and carotenoid-containing vegetables (carrots, tomatoes) seem to offer protection.
A high dietary intake of the carotenoid compound lutein has been found to lower the risk of colon cancer, especially in women. The major sources of lutein consumed by study participants were spinach, broccoli, lettuce, tomatoes, oranges, carrots, celery and greens.
Vegetables contain many substances that may keep the bowel healthy. Beta-carotene, lutein, B vitamins, vitamin C and other natural plant chemicals all may have anticancer properties. Vegetables are also rich in fiber. And certain vegetables such as asparagus and Jerusalem artichokes may promote the growth of health-enhancing bacteria in the intestinal tract.
Green Tea. Research suggests that antioxidant compounds in green tea may prevent colon cells from becoming cancerous. Population studies have shown that drinking green tea is associated with lower rates of colon and rectum cancer. While we don't yet know if drinking green tea over the long term will decrease your risk of getting colon or rectal cancer, current evidence indicates that this beverage offers protection. Try adding a cup of green tea to your daily diet-replace coffee, soft drinks and fruit drinks with green tea. It's available loose in specialty tea shops or in tea bags in grocery stores.
Alcohol. There is evidence that all types of alcoholic beverages increase the risk of colorectal cancer. When it comes to rectal cancer in men, beer may be more harmful than other types of alcohol. It's thought that alcohol may stimulate colon cells, causing them to rapidly divide, and it may activate cancer-causing substances. Alcohol may also stimulate the transformation of polyps into cancer.
Cancer experts do not recommend the consumption of alcohol. If you drink, limit yourself to no more than two drinks per day or a maximum of nine per week (men), and one drink per day or seven per week (women).
Vitamins C and E. An intake of foods rich in these two nutrients has been linked with a lower risk of colorectal cancer. A study conducted among Iowa women found that those with the highest intake of vitamin E had an 84 percent lower risk of the cancer compared with women who consumed the least. Vitamin E was particularly protective in women under the age of 65. One Finnish study found that vitamin E supplements offered protection from colorectal cancer in men.
Foods rich in vitamin C include citrus fruit, citrus juices, cantaloupe, kiwi, mango, strawberries, broccoli, Brussels sprouts, cauliflower, red pepper and tomato juice. To supplement, take 500 or 600 milligrams once daily. Keep in mind that studies have not found vitamin C supplements to lower cancer risk; only high intakes of foods containing vitamin C have been linked to a lower risk of colorectal cancer.
The best food sources of vitamin E are wheat germ, nuts, seeds, vegetable oils, whole grains and leafy greens. To supplement, take 200 to 800 international units (IU) of natural source vitamin E once daily. Preliminary research in the lab suggests that supplements labeled 'mixed' vitamin E may offer additional cancer protection.
Folate. A deficiency of this B vitamin has been linked with colorectal cancer. Folate is essential for the production of a cell's genetic material, DNA (deoxyribonucleic acid), in cells. DNA is the blueprint in every cell that controls cell division and all body processes. A lack of folate may also make the harmful effect of alcohol on colon cells more pronounced.
Folate-rich foods include spinach, lentils, orange juice, whole grains, fortified breakfast cereals, asparagus, artichoke, avocado and seeds. To supplement, take a multivitamin and mineral that contains 400 to 1000 micrograms of folic acid (the synthetic form of folate) or take a B complex formula.
Calcium. Several studies have linked higher calcium intakes from supplements (1200 to 2000 milligrams per day) and low-fat dairy foods with lower risks of colorectal cancer and recurrence of polyps. It is thought that once calcium is ingested, the mineral binds with bile acids in the intestinal tract, thereby preventing their toxic effects on colon cells.
Be sure to meet your daily calcium requirements by eating three to four one-cup servings of low-fat yogurt or milk. If you don't eat dairy foods, calcium-fortified soy or rice beverages and orange juice can be substituted. For each serving your diet lacks, take a 300 milligram calcium supplement with vitamin D added.
Garlic. A daily intake of raw and cooked garlic and its accompanying sulfur compounds is associated with a lower risk of colon and rectal cancer. The Iowa Women's Health Study, which followed 42,000 women for five years, found that women who consumed 0.7 grams of garlic per day (less than one clove) had a 32 percent lower risk of colon cancer compared with those who did not consume garlic.
Garlic may help prevent cancer in a number of ways. Like vitamins C and E, garlic possesses antioxidant properties, which may keep DNA healthy. The sulfur compounds in garlic may also help the liver detoxify cancer-causing substances. Garlic may have a direct toxic effect on certain types of cancer cells. And finally, studies have shown that garlic, in particular the allyl sulfides in aged garlic extract, stimulate the body's immune system.
Include one to two cloves of cooked or raw garlic in your daily diet. To supplement, buy aged garlic extract. The aging process used to make this supplement increases the concentration of the sulfur compounds that stimulate the immune system. Aged garlic is also odor free and gentler on the stomach. Generally, two to six capsules a day (one or two with meals) are recommended. You can also buy aged garlic in a liquid form (Kyolic' brand) that you add to foods.
Canadian Cancer Society
Colon Cancer Alliance, Inc.
Colorectal Cancer Association of Canada
Ottawa Regional Cancer Center
A service provided by National Cancer Institute (www.nci.nih.gov)
National Cancer Institute
The above excerpt is from "Leslie Beck's Nutrition Encyclopedia" (Penguin Canada, 2001/2003), available at bookstores across the country. The following is copyrighted and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or means - electronic, mechanical, photocopying, or likewise.
All research on this web site is the property of Leslie Beck Nutrition Consulting Inc. and is protected by copyright. Keep in mind that research on these matters continues daily and is subject to change. The information presented is not intended as a substitute for medical treatment. It is intended to provide ongoing support of your healthy lifestyle practices.