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.