Fiber, a natural substance found in plant foods such as berries, beans, nuts, oats and bran, is an important component of a healthy diet. Known for its beneficial effects on blood cholesterol levels, fiber is also credited with promoting intestinal health and regular bowel movements as well as regulating blood sugar and appetite control.

Various studies have shown that a diet rich in fiber appears to reduce the risk of digestive system disorders including constipation, diarrhea, gallstones, diverticular disease, irritable bowel syndrome and colorectal cancer. Other conditions for which fiber appears to reduce risk include heart disease, diabetes and obesity.

High-fiber foods are a rich source of vitamins and minerals, and are generally low in total fat, cholesterol and sodium. Foods high in fiber generally have few calories. They also contribute to a feeling of fullness.

According to the American Dietetic Association, most people consume only about 11 grams of dietary fiber per day. In addition, less than 15 percent of Americans include at least one serving of whole grains in their daily diets. This amount is about half the intake recommended by health experts. The Food and Nutrition Board of the U.S. National Academy of Sciences recommends that people consume 25 to 35 grams of fiber a day. To get adequate fiber, health experts recommend that people consume a variety of fruits, vegetables and whole-grain products daily.

Fiber is a substance found in plant foods - whole grains, fruits, vegetables, beans, nuts and seeds - that the body cannot digest. Fiber, also referred to as dietary fiber, essentially has no calories, because it is not absorbed by the body. Instead, it passes through the digestive system largely intact.

Fiber is generally separated into two groups based on its solubility (ability to dissolve) in water. Soluble fiber turns to a gel when mixed in a fluid. For instance, gums and pectins are soluble fibers and are found in beans, oats, barley, and some fruits and vegetables. Insoluble fibers, such as cellulose and hemicellulose, do not dissolve in liquids and are typically found in most whole wheat and grain products, in addition to vegetables.

Fiber is found in plants. It is not present in animal products such as milk and other dairy products, eggs, meat, poultry and fish. Sources of fiber include:

• Skins
• Membranes
• Seeds
• Bran

Foods with high fiber content include:

• Whole-grain cereals and breads
• Fruits
• Vegetables
• Legumes (dried peas and beans)

The benefits of soluble fiber include:

• It dissolves in water, turning into gel. This slows the digestion and absorption of nutrients, and allows glucose to be slowly and steadily released into the bloodstream.
  
  
• It soaks up excess bile acids in the intestinal tract. Bile acids are made in the liver from cholesterol. A type of soluble fiber called pectin binds to fatty substances in the digestive tract. Bile acids bound to fiber are excreted in the stool. This causes more cholesterol to be used to make bile acid, leading to an overall lowering of blood cholesterol levels.
  
  

  

• It delays stomach emptying, which makes a person feel full (satiated).

Insoluble fiber (also known as roughage) helps to regulate gastrointestinal functions, keeping the colon clean. It cannot be dissolved, and instead pushes waste through the intestines.

Fiber is a key element of a healthy diet. It can help contribute to good digestive health and appetite control, while also playing an essential role in the prevention or management of many digestive disorders, including constipation, hemorrhoids, diarrhea, irritable bowel syndrome, fecal incontinence, gallstones, diverticular disease and colorectal cancer. Research also indicates that a high-fiber diet may help prevent or manage other conditions such as diabetes, obesity and heart disease.

Foods high in fiber, such as fruits, vegetables and whole grain foods are naturally cholesterol-free and generally low in fat, sodium and calories (energy). In addition, these foods are full of vitamins and minerals, carbohydrates and protein, all of which have a significant impact on an individual’s health, especially that of the digestive system.

There are various components or nutrients found in plant foods that are beneficial to a person’s health. Typically, these benefits are the result of those ingredients that are eaten, absorbed and used by the body to function properly. For instance, vitamins and minerals, fats, proteins and calories (energy) are absorbed from foods and enable the organs to function and sustain life.

Fiber, also referred to as dietary fiber, differs from other nutrients in that it is not absorbed by the body, passing instead through the entire digestive system largely intact. However, fiber is an important dietary component that can help contribute to good health, especially that of the digestive system. A fiber-rich diet full of whole grains, beans, vegetables and fruits is naturally low in cholesterol, salt and fat and rich in vitamins, minerals and antioxidants (substances that protect against cancer-causing agents).

The various health benefits of dietary fiber can be partially explained by its ability to dissolve in liquids. For example, soluble fiber forms a gel when mixed in a liquid. The viscosity (a measure of a fluid’s resistance to flow) of soluble fiber in some foods has been credited with its cholesterol-lowering effect. After a meal, bile acids rich in cholesterol are secreted into the intestines and mix with the food to help in digestion and absorption. As food is absorbed, the remaining viscous soluble fiber interferes with the reabsorption of these cholesterol-rich bile acids from the intestines. The end result is that the cholesterol is removed from the body and blood cholesterol levels are reduced.

Dietary fiber has an added benefit of being good for the alimentary canal. It adds bulk to and softens the stool, facilitating its exit through the rectum. Constipation is a common problem, especially among the elderly. A high-fiber diet can help relieve constipation and promote regular bowel movements. Alternately, because fiber also absorbs water, it can help solidify the stool of patients experiencing diarrhea.

Fiber can also reduce the risk of diverticulosis – a condition in which small pockets form in the colon – and the inflammation of these pockets which leads to diverticulitis (both conditions are known as diverticular disease). In fact, psyllium seed husk, a good source of soluble fiber, is often used in nutritional supplements and in certain bulking agents (laxatives). It is important to drink plenty of liquids while eating foods that are very high in soluble fiber, especially psyllium seed husk. A diet rich in fiber can also help prevent other digestive disorders including hemorrhoids, irritable bowel syndrome, gallstones and colorectal cancer. 

Because dietary fiber can slow the movement and absorption of foods from the intestines, it also has a favorable effect on blood sugar (glucose) levels after eating. Research also indicates that a high-fiber diet can reduce insulin (a hormone that lowers levels of glucose in the blood) requirements and increase insulin resistance. This improves blood sugar levels and decreases a person’s risk of diabetes. The secondary benefits of a high-fiber diet to reduce the risk of chronic illnesses may include its lower calorie (energy), fat and simple carbohydrate content, which aid in weight management

Fiber is an important part of a healthful diet. However, according to the American Dietetic Association, most people consume only about 11 grams of fiber a day. This amount is among the lowest intake levels in the world and is about half the intake recommended by health experts.

Fiber is best obtained from foods rather than from a nutritional supplement. In addition to providing both soluble and insoluble dietary fiber, plant foods contain many other nutrients that are beneficial to health, such as vitamins and minerals and other phytochemicals (e.g., plant chemicals) that may not be included in a supplement.

Fiber supplements can decrease the absorption of certain medications, including digoxin (a drug used for treating heart conditions), aspirin, carbamazepine (a drug used to control seizures), lithium (a drug used to treat bipolar disorder), warfarin (a drug used to prevent the blood from clotting) and nitrofurantoin (an antibiotic used to treat urinary tract infections).

In addition, fiber supplements can reduce glucose (blood sugar) levels. Therefore, people with diabetes may need an adjustment in their insulin dosage when taking these supplements. Fiber supplements can also decrease the absorption of nutrients such as calcium, iron, magnesium or zinc. As with any supplement, it is important that patients consult their physician about any possible interactions or side effects.

To increase the intake of dietary fiber, people are encouraged to include plenty of whole-grain breads and cereals, as well as fresh fruits, vegetables and dried beans, in their daily diet. Health experts generally recommend eating two to four servings of fruit, three to five servings of vegetables and six to 11 servings of whole grains and cereals each day.

The Food and Nutrition Board (FNB) of the U.S. National Academy of Sciences (NAS) recommends that adults 19 years and older consume 21 to 38 grams of total fiber in their daily diet to protect against the risk of digestive system disorders including hemorrhoids, irritable bowel syndrome, diverticular disease and colorectal cancer.

Good sources of fiber include:

Nuts are also a good source of fiber and protein, but they are also high in fat and calories. However, these fats are mostly unsaturated fats, which do not increase levels of blood cholesterol or triglycerides (fatty substances in the blood and tissues), and research suggests that eating nuts may even help reduce these levels. 

As a general rule, food products that contain at least 5 grams (g) of fiber per serving are excellent sources of fiber. Foods that contain 2.5 g to 4.9 g are good sources of fiber.

It is important that patients increase dietary fiber content gradually in order to allow the digestive tract to adjust. Side effects of increasing fiber intake too rapidly are generally mild and may include excess gas formation, constipation, bloating and/or diarrhea. However, the natural bacteria in the digestive tract will eventually adjust to the increase in fiber in the diet. It is also important to drink plenty of fluids when increasing the amount of fiber in one’s diet. This will reduce the risk of constipation that can result from increasing fiber intake.

The prospect of dramatically increasing the amount of fiber in one’s diet can be intimidating. Tips for making the transition easier:

• Add a little fiber each day while building up to the recommended level. For example, sprinkle bran or raisins onto breakfast cereal.
  
  
• Chew slowly. This allows fiber compounds to break down, making them easier to digest.
  
  
• Raw vegetables and fruits are preferable. Boiling too long can strip foods of up to half of their fiber content. Steaming or stir-frying these foods can preserve more of the fiber. Skins should also be left on fruits and vegetables whenever possible.
  
  
• Juice (such as orange or grapefruit juice) does not have the same fiber as the whole fruit when pulp has been strained away.
  
  
• Pureeing does not destroy fiber.
  
  
• Choose high-fiber cereals when possible. These contain 5 or more grams of fiber per serving. Adding fresh fruit can contribute an additional 1 or 2 grams of fiber.
  
  
• Choose whole grains. Not all wheat bread is whole-wheat bread. Make sure the ingredient label says “whole wheat.”
  
  
• Add beans to salads, soups and stews.
  
  
• Add bran cereal to muffins, breads and casseroles.
  
  
• Instead of using all-purpose flour, substitute oat bran for one-third of the recommended ingredient.
  
  
• Snack on fruit or fresh vegetables.
  
  
• Add one or two tablespoons of wheat germ to yogurt, salads or cereal. Each tablespoon contains a gram of fiber.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following fiber-related questions:

1. How might increasing my fiber intake benefit my health?
   
   
2. How much total fiber do I need to consume daily?
   
   
3. Which type of fiber do you recommend I increase in my diet?
   
   
4. Which foods contain the type of fiber you recommend for me?
   
   
5. Is it possible for me to eat too much fiber? What, if any, negative effects might I feel?
   
   
6. How quickly do you recommend I increase my fiber intake?
   
   
7. Are there any signs or symptoms I should report to you while increasing my fiber intake?
   
   
8. Do you recommend that I take fiber supplements?
   
   
9. Can fiber supplements interact with any prescription medications I am currently taking?
   
   
10. Are there any over-the-counter medications I should avoid when taking fiber supplements?