Dietary fiber is plant residue that passes through the intestinal tract undigested. Just as there are many types of plants, there are also many types of fiber. Fiber may be soluble (oat bran, psyllium) and form a gelatinous bulk that has cholesterol-lowering properties, or it may be insoluble (wheat and other grains), which adds bulk to the stool. Both are beneficial and important.
Function of the Large Intestine
The principal function of the large intestine (colon) is to remove excess water from food wastes passing into it from the small intestine. If food passes through the large intestine too quickly for water to be absorbed, diarrhea can result. In contrast, if waste material passes too slowly, too much water is absorbed. This can result in hard stools and the need to strain to have a bowel movement.
Importance of Dietary Fiber
Fiber, also called roughage or bulk, is necessary to promote the wave-like contractions that move food through the intestine. As fiber passes through the intestine undigested, it absorbs many times its weight in water, resulting in softer and bulkier stools. In order for the process to be successful, adequate fluid intake (8 to 10 glasses per day) is essential.
Rural Africans, whose diets are rich in fiber, suffer less from digestive tract diseases than Americans do; it is thought this may be partially related to the nature of their diet. Most Americans eat 10 to 15 grams of fiber a day, whereas 25 to 35 grams are recommended. High-fiber foods, such as fruits and vegetables, tend to be low in calories, so weight gain should not be a problem.
High-Fiber Diet and Hemorrhoids
Hemorrhoids are a collection of small arteries and veins in the anal region. We are all born with a ring of hemorrhoids on the outside of the rectum and a ring just inside the rectum. Hard stools and straining cause hemorrhoids to enlarge, which can lead to bleeding and pain. In addition, hemorrhoidal tissue may protrude through the rectal opening (anal canal). A high-fiber diet results in a large, soft, bulky stool that passes through the colon easily and quickly. A softer, larger stool helps prevent straining, which can help avoid or relieve hemorrhoidal symptoms.
High-Fiber Diet in Irritable Bowel Syndrome
Irritable Bowel Syndrome, sometimes called spastic colon or IBS, is one of the most common disorders of the lower digestive tract. The colon appears normal in Irritable Bowel Syndrome, but it overreacts to various stimuli. The symptoms include altered bowel habits (constipation, diarrhea or both alternately), abdominal pain, cramping and spasms. Acute episodes can be triggered by emotional tension and anxiety, specific foods, and certain medications. Increased amounts of fiber in the diet can help relieve symptoms by producing soft, bulky stools and helping to normalize the time the stool takes to pass through the colon. Because the same symptoms occur in other disorders, careful evaluation is necessary to exclude other diagnoses.
High-Fiber Diet and Colon Polyps/Cancer
Colon cancer is a major health problem. Most colon cancer begins as a colon polyp, a benign growth that in some people may become cancer. Colon cancer is preventable if polyps are removed at an early stage. It is now known that heredity plays an important role in who develops colon cancer, but there are other factors involved as well. Countries with diets high in fiber and low in fat have a low incidence of colon cancer. One theory is that cancer-causing chemicals (carcinogens) in the diet remain in contact with the colon wall for a longer time and in higher concentrations when the diet is low in fiber. A large, bulky stool acts to dilute these carcinogens and to move them through the bowel more quickly.
High-Fiber Diet and Diverticulosis
Colon diverticulosis occurs when pockets or sacs protrude from the bowel wall. These diverticula occur gradually over time and are due to excessive pressure or spasms within the bowel. These pockets usually cause no problems, but sometimes they rupture and become infected (diverticulitis) or even perforate cause an abscess or peritonitis. A high-fiber diet results in a large, soft, bulky stool that passes through the bowel easily and quickly. Therefore the colon does not need to generate as much pressure to propel stool through it. Diverticula formation may be reduced or even stopped.
High-Fiber Diet and Cholesterol
As noted above, fiber generally is divided into two categories: insoluble fiber found in wheat bran and cellulose from vegetables and fruits and soluble fiber commonly found in oatmeal, oat bran, guar gum, psyllium seed, fruit pectin and gum arabic. Soluble fiber helps to lower blood cholesterol by binding with the cholesterol (which comes from the liver) and carrying it away in the stool. Oat bran cereal and breads are good sources of soluble fiber.
High-fiber foods can be found in several food groups.
- Legumes: The bean family excels in fiber, especially the soluble, cholesterol-lowering type. They include kidney, pinto, navy, lima and baked beans.
- Whole grains: Wheat bran and oat bran are present in a variety of cereals and breads. The label should say that the bread contains whole wheat or whole grain. Plain wheat bread may lack fiber. One cannot always tell by the color. Some manufacturers artificially color bread brown to make it look more wholesome.
- Whole fresh fruits: The valuable pectin fiber is found in the skin and pulp. Figs, prunes and raspberries have the highest fiber content.
- Cooked or stewed fruits: Prunes and applesauce are good choices.
- Green leafy vegetables: Spinach, celery, and broccoli are good examples.
- Root vegetables: Potatoes, turnips and carrots are excellent sources.
Since fiber can cause rumbling intestinal gas and even some mild cramping, the amount taken should be increased gradually. The goal should be 25 to 35 grams of fiber per day, which will usually produce one or two soft, formed stools per day. The following are good general rules:
- Drink plenty of liquids, including water, fruit or vegetable juices (8-10 glasses per day). Increasing the amount of fiber without adequate liquid will result in hard stools. Because caffeine acts as a mild diuretic, caffeine- containing products should not be considered part of your liquid intake.
- Eat meals at regular intervals.
- Get regular exercise.
A Dietary Fiber Supplement May Be Helpful
Some people do not tolerate fibrous foods well. Fiber supplements can be a convenient alternative. These products are plant fiber that absorb water and produce the bulk necessary for the digestive tract to perform naturally. If you do not get enough fiber in your diet, you can take a supplement. These fiber supplements, in conjunction with foods, are a readily available way to reach the fiber goal of 25 to 35 grams per day.
For more information about dietary fiber,
Position of the American Dietetic Association: Health implications of dietary fiber