What Is Dietary Fiber?

Dietary fiber comes from the portion of plants that is not digested by enzymes in the intestinal tract. Part of it, however, may be metabolized by bacteria in the lower gut.

Different types of plants have varying amounts and kinds of fiber, including pectin, gum, mucilage, cellulose, hemicellulose and lignin. Pectin and gum are water-soluble fibers found inside plant cells. They slow the passage of food through the intestines but do nothing to increase fecal bulk. Beans, oat bran, fruit and vegetables contain soluble fiber.

In contrast, fibers in cell walls are water insoluble. These include cellulose, hemicellulose and lignin. Such fibers increase fecal bulk and speed up the passage of food through the digestive tract. Wheat bran and whole grains contain the most insoluble fiber, but vegetables and beans also are good sources.

Sometimes there is confusion as to the difference between crude fiber and dietary fiber. Both are determined by a laboratory analysis, but crude fiber is only one-seventh to one-half of total dietary fiber.

The American Heart Association recommends eating a variety of food fiber sources. Fiber is important for the health of the digestive system and for lowering cholesterol. Foods containing fiber often are good sources of other essential nutrients. Depending on how they’re prepared, these foods can also be low in trans fat, saturated fat and cholesterol. Fruits, vegetables, whole-grain, high-fiber foods, beans and legumes are good sources of both soluble and insoluble dietary fiber. The AHA recommends that at least half of grain intake come from whole-grain foods.

Dietary fiber intake among adults in the United States averages about 15 grams. The Institute of Medicine recommends consuming 14 grams of fiber for every 1,000 calories you need.

To improve your diet, add foods that contain more dietary fiber. You can include some or all of the following:

  1. Whole-grain foods (such as bran cereals) and breads (those made with whole wheat grains).
  2. Fresh fruits (including the skin and pulp).
  3. Dried or stewed fruits (such as prunes, raisins, or apricots).
  4. Root vegetables (such as carrots, turnips, or potatoes).
  5. Raw or fresh vegetables, such as cabbage. (Lettuce is actually low in fiber.)

Eating bran cereal in the morning is often the easiest way to obtain fiber. All-Bran, 100% Bran, Bran Buds, oat bran, oatmeal, and Raisin Bran are some of the high-fiber cereals presently available. Bran can cause rumbling intestinal gas and even some mild cramping, so it should be eaten in small amounts at first. The amount can be increased as the body gets used to it. The goal should be one to two large, soft, formed stools a day.

You should also try to follow these dietary rules:

  1. Drink plenty of liquids, including fruit or vegetable juices and water. Drink at least six cups of water or fluid a day.
  2. Eat slowly. Chew your food thoroughly. This allows the saliva and digestive juices of the stomach, liver, and pancreas to break down food more easily. It may also help prevent problems from developing in the lower digestive tract.
  3. Eat your meals at regular intervals.

Benefits of Fiber

Insoluble fiber binds water, making stools softer and bulkier. Therefore, fiber, especially that found in whole grain products, is helpful in the treatment and prevention of constipation, hemorrhoids and diverticulosis. Diverticula are pouches of the intestinal wall that can become inflamed and painful. In the past, a low-fiber diet was prescribed for this condition. It is now known that a high-fiber diet gives better results once the inflammation has subsided.

Low blood cholesterol levels (below 200 mg/dl.) have been associated with a reduced risk of coronary heart disease. The body eliminates cholesterol through the excretion of bile acids. Water-soluble fiber binds bile acids, suggesting that a high-fiber diet may result in an increased excretion of cholesterol. Some types of fiber, however, appear to have a greater effect than others. The fiber found in rolled oats is more effective in lowering blood cholesterol levels than the fiber found in wheat. Pectin has a similar effect in that it, too, can lower the amount of cholesterol in the blood.

Other claims for fiber are less well founded. Dietary fiber may help reduce the risk of some cancers, especially colon cancer. This idea is based on information that insoluble fiber increases the rate at which wastes are removed from the body. This means the body may have less exposure to toxic substances produced during digestion. However, more recent studies have not confirmed the protective effects of fiber in developing colon cancer. A diet high in animal fat and protein also may play a role in the development of colon cancer.

High-fiber diets may be useful for people who wish to lose weight. Fiber itself has no calories, yet provides a “full” feeling because of its water-absorbing ability. For example, an apple is more filling than a half cup of apple juice that contains about the same calories. Foods high in fiber often require more chewing, so a person is unable to eat a large number of calories in a short amount of time.

How Much Fiber?

The average American consumes 14 grams of dietary fiber a day, which is considerably less than the recommended level. The current recommendations, according to the 2005 Dietary Guidelines for Americans, is 14 grams of fiber per 1000 calories consumed. So, if you consume a 2500 calorie diet, you should eat approximately 35 grams of fiber per day. Also, fiber intake may vary depending on age and gender.

Fiber and Diverticulosis

Prolonged, vigorous contraction of the colon, usually in the left lower side, may result in diverticulosis. This increases pressure causing small and eventually larger ballooning pockets to form. These pockets usually cause no problems. However, sometimes they can become infected (diverticulitis) or even break open (perforate) causing pockets of infection or inflammation of the sac lining the abdomen (peritonitis). A high-fiber diet may increase the bulk in the stool and thereby reduce the pressure within the colon. By so doing, the formation of pockets is reduced or possibly even stopped.

Some professionals recommend restricting the following foods in diverticulosis diets: nuts, poppy seeds, caraway seeds, rye seeds, popcorn, crunchy peanut butter, corn, cucumber, and squash; as well as fruits and vegetables with seeds such as strawberries, figs, and tomatoes. However, there has never been any medical proof that these foods are injurious. Many gastroenterologists allow and even encourage consuming these foods, depending on an individual’s tolerance.

Fiber, Cholesterol and Gas

Insoluble fiber is found in wheat, rye, bran, and other grains.

It is also the fiber found in most vegetables. Insoluble fiber means it does not dissolve in water. It also cannot be used by intestinal-colon bacteria as a food source, so these beneficial bacteria generally do not grow and produce intestinal gas.

Soluble fiber, on the other hand, does dissolve in water forming a gelatinous substance in the bowel. Soluble fiber is found in oatmeal, oat bran, fruit, psyllium (Metamucil, Konsyl), barley, and legumes. Soluble fiber, among its other benefits, seems to bind up cholesterol allowing it to be eliminated with the stool. If enough is removed it can lower the blood cholesterol 10-15%.

The down side of soluble fiber is that it can be metabolized by gas forming bacteria in the colon. These bacteria are harmless but for those who have an intestinal gas or flatus problem it is probably best to avoid or carefully test soluble fibers to see if they are contributing to intestinal gas.

Sources: American Heart, Gicare

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