Dietary Fiber “In a Nutshell”

Jessica Iannotta

While the term carbohydrate often carries a negative connotation with respect to health and nutrition, there are actually many healthy sources of carbohydrates that are rich in essential nutrients, phytochemicals, and dietary fiber, all of which are an important part of a healthy diet. These healthy sources of carbohydrates include most vegetables as well as beans, fruits, whole grains, nuts, and seeds.  Today’s blog focuses on fiber and its many beneficial properties as well as its use in minimizing digestive-related side effects of cancer treatment.

Dietary fiber is the indigestible portion of plant foods and includes soluble and insoluble fiber.  Most sources of dietary fiber include some of both type of fiber.  Foods containing fiber contain nutrients that are associated with lower health risk and healthier eating habits.1   High intake of dietary fiber, in particular cereals and whole grains, is also associated with a lower risk of colon cancer, specifically because fiber can cleanse the colon of potential carcinogenic compounds.2

Insoluble fiber

Most dietary fiber is the insoluble type which is not digested nor absorbed and is, instead, passed through the body, which leads to more regular bowel movements and increased intestinal transit time.  Insoluble fiber comes from plant cell walls and does not dissolve in water.  It is often recommended to treat digestive problems like constipation and IBS because of its laxative effect and ability to provide bulk to the stool. While in the intestines it modulates the digestion of other foods. It is important to note that all fiber, and importantly insoluble fiber, must be consumed along with adequate fluid in order to avoid blockage or worsened constipation.

Sources of insoluble fiber include whole wheat, whole grains, wheat bran, corn bran, seeds, nuts, brown rice, zucchini, broccoli, cabbage, tomato, green beans, leafy green vegetables, raisins, and skin of potatoes and tomatoes.

Soluble fiber

Soluble fiber is made up of a group of carbohydrates that can dissolve in water.  It is helpful in the management of diarrhea and fecal incontinence since it forms a gel and can help absorb extra fluid in the gastrointestinal tract.  Soluble fibers are also fermented by bacteria in the gut and promote the maintenance of healthy gastrointestinal flora.  It can also help lower the risk of heart disease by reducing blood cholesterol levels.  By helping control blood glucose levels, soluble fiber can aide in the management of type 1 and type 2 diabetes as well.3  Soluble fiber is also helpful for weight management by slowing digestion and delaying the emptying of the stomach to promote satiety and prevent overeating.

Sources of soluble fiber include oatmeal, oat cereal, oat bran, barley, rye, potato, apples, bananas, oranges, pears, strawberries, blueberries, cucumber, celery, carrot, almonds, flaxseed, beans, dried peas, lentils, and psyllium.

Dietary Fiber and the Cancer Patient

Dietary fiber is very important to help manage digestive side effects associated with cancer treatment.  Soluble fiber is frequently recommended to help minimize diarrhea associated with chemotherapy and radiation, especially for those with digestive cancers.  Insoluble fiber is recommended to help prevent and treat constipation, which is a common side effect of many anti-nausea medications.

Stay tuned for future blogs that will discuss more about the role of dietary fiber, along with other suggestions, in the management of diarrhea and constipation associated with cancer treatment.


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1. Rock, C. L., Doyle, C., Demark-Wahnefried, W., Meyerhardt, J., Courneya, K. S., Schwartz, A. L., Bandera, E. V., Hamilton, K. K., Grant, B., McCullough, M., Byers, T. and Gansler, T. (2012), Nutrition and physical activity guidelines for cancer survivors. CA: A Cancer Journal for Clinicians, 62: 242–274.

2. Norat T, Kampman E, Greenwood D, Vieira R, Lau R, Chan DM, Aune D. (2011) Dietary fibre, whole grains and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies.  British Medical Journal 343: 6617

3. Wald, Arnold. “Patient Information: High-fiber Diet (Beyond the Basics).” Patient Information: High-fiber Diet (Beyond the Basics). Montefiore Hospital, Web. 11 July 2012. Accessed August 8, 2012.

4. Zelman, KM.  “The Benefits of Fiber: For Heart, Weight and Energy” WebMD. Accessed August 9. 2012.

Blog category: 
-> Nutrition


Thanks Jessica - your article simplifies the fiber story for me, by relating it to precisely what I'm experiencing since I've begun treatment with xalcori, and prochlorperazine.

Thanks again!

Jim Watson
Portland, Maine

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