What is fiber? Does it help prevent cancer?

Cancers treated or prevented:
Colorectal cancers, spastic bowel syndrome

Delivery routes: Fruits, vegetables, leafy greens, grains, or oral supplements as tablets or liquid form

How this substance works: Fiber in diets helps maintain optimal movement of food and wastes through the lower human digestive tract. Fiber helps cleanse the intestinal tract and colon, preventing the formation of pockets of residue. There are two basic types of dietary fiber, insoluble fiber and soluble fiber. Water-soluble fiber absorbs water in the intestines and via enzymatic activity mixes food into a gel on which intestinal enzymes work. Conversely, insoluble fiber is the more valuable in reducing risk of cancer as it is considerably more difficult to digest; thus carcinogens and toxins in the food are not released in the presence of the metabolically active cells of the intestinal lining but rather pass harmlessly out of the body. It follows that the less time carcinogens are in contact with the intestinal walls, the lower the risk of cancer should be because of decreased exposure to carcinogens carried in food and food wastes.

Insoluble fiber is sometimes referred to as the “scrub brush” for the human internal digestive tract because it “scrubs” the intestines clean as it passes through the small intestine and colon. This type of fiber acts to absorb many times its own weight in water, which softens the waste in the intestine and facilitates motion through the body, thereby decreasing irritation, constipation, and blockage.

Research has shown that fiber increases peristalsis, the involuntary muscular contractions of the digestive system. Regular and efficient peristalsis resulting from increased bulk in soft stools decreases the period of time that toxins are in contact with intestinal tissue. Fiber may also bind to carcinogens, lessening their proximity to internal cells. Water absorbed by fiber dilutes toxins, rendering them less harmful and decreasing the risk of cancer. Fiber can also help absorb intestinal acids such as bile, hydrochloric acid, and other irritants that may predispose cells to disease. Fiber can promote intestinal health by encouraging the growth of beneficial bacteria while discouraging the growth of harmful bacteria. A high-fiber diet may also reduce the incidence of diverticulosis and irritable bowel syndrome, both implicated in intestinal cancer.

Human studies suggesting an inverse relationship between insoluble dietary fiber intake and colorectal cancer incidence remain inconclusive because of the complexity of the disease. Many other factors, including heredity and lifestyle, play a role in the appearance of disease. An overwhelming majority of the long-term cohort studies, however, have pointed to dietary fiber as a means of reducing the risk for colorectal cancer.

Side effects: Some studies also show that excessive amounts of fiber may interfere with the absorption of certain minerals such as calcium, copper, iron, magnesium, selenium, and zinc. Excessive dietary fiber may also lead to constipation and occasional blockage. The frequency and intensity of both of these negative side affects can be reduced with the use of softening agents such as psyllium.

Bibliography

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Aune, D., et al. "Dietary Fibre, Whole Grains, and Risk of Colorectal Cancer: Systematic Review and Dose-Response Meta-Analysis of Prospective Studies." British Medical Jour. 343 (2011): d6617. PubMed.gov. Web. 21 Oct. 2014.

Evert. Alison. "Diet and Cancer." MedlinePlus. US NLM/NIH, 18 June 2013. Web. 21 Oct. 2014.

Kushi, L. H., et al. "American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention: Reducing the Risk of Cancer with Healthy Food Choices and Physical Activity." CA: A Cancer Jour. for Clinicians 62.1 (2012): 30–67. PubMed.gov. Web. 21 Oct. 2014.

Park, Y., et al. "Dietary Fiber Intake and Risk of Colorectal Cancer: A Pooled Analysis of Prospective Cohort Studies." JAMA 294.22 (2005): 2849–2857. PubMed.gov. Web. 21 Oct. 2014.

Vorvick, Linda J. "Fiber." MedlinePlus. US NLM/NIH, 14 Aug. 2012. Web. 21 Oct. 2014.