Dietary fiber, found in all plant-based foods, plays an essential role in human health. Most whole foods contain a combination of the two types of fiber, soluble and insoluble. Both types of fiber help maintain the health of your digestive system and promote regular bowel movements.
Soluble fiber pulls in water to form a gel in the digestive tract. This slows digestion, so your stomach and intestine do not absorb as much of some nutrients, like starch and sugar. As a result, cholesterol levels go down over time, which may help prevent heart disease and stroke. Consuming soluble fiber may also improve glucose tolerance in people with diabetes. This type of fiber is a common ingredient in many over-the-counter laxatives. Psyllium husk (which contains both soluble and insoluble fiber), pectin, and the soft parts of fruits, dried beans, and peas are examples of soluble fiber.
Insoluble fiber, on the other hand, can be found in the peels of fruit, such as apples, blueberries, and grapes. It acts as a natural laxative that speeds the passage of foods through the stomach. It also gives stool its bulk and helps it move quickly through the gastrointestinal tract.
Studies suggest that getting more fiber in your diet may play a role in the treatment of conditions such as gastrointestinal disease, constipation, hemorrhoids, high cholesterol, heart disease, stroke, diabetes, and some forms of cancer. Most Americans do not get the recommended amount of fiber (25 to 35 g. per day) in their daily diet.
Many studies show that fiber relieves constipation. Researchers think fiber relieves constipation by adding bulk to stool and helping it move faster through the intestines. If you have impacted stool, which is a complication of constipation, DO NOT take fiber supplements without talking to your doctor first.
Fiber can be used to relieve mild-to-moderate diarrhea. Soluble fiber soaks up water in the digestive tract, which makes stool firmer and slower to pass.
Irritable bowel syndrome (IBS)
Several studies show that soluble fiber helps regulate stool frequency and consistency in people with IBS. Psyllium and bran are the best studied soluble fiber sources in the treatment of IBS.
Your doctor may recommend soluble fiber to help soften stool and reduce the pain associated with hemorrhoids.
Inflammatory bowel disease (IBD)
A clinical study of people with ulcerative colitis (a type of IBD) found that psyllium seeds were as effective as the prescription drug mesalamine (Rowasa) in reducing recurrences of the disease. Speak to your doctor about the right form and dosage of fiber.
People with diverticulosis often take fiber supplements to prevent constipation and stop the condition from progressing. The National Academy of Nutrition and Dietetics recommends 25 to 30 g. of fiber per day. Your doctor may recommend more. Some researchers think that people with diverticulosis should avoid foods such as nuts and pumpkin, caraway, and sesame seeds. They believe these small particles may get lodged in the diverticula (pouches in the colon) and cause infection and irritation.
Soluble fibers, such as those in psyllium husk (which contains both soluble and insoluble fiber), guar gum, flaxseed, and oat bran, can help lower cholesterol when added to a low saturated fat, low cholesterol diet. Clinical studies show that psyllium in particular is effective in lowering total cholesterol levels as well as LDL (bad) cholesterol levels.
Studies show that a high fiber diet may help prevent type 2 diabetes, lower insulin and blood sugar levels, and improve cholesterol and triglyceride (fats in the blood) levels in people with diabetes. In addition, one well-designed clinical study suggests that pregnant women with type 1 diabetes may be able to reduce the amount of insulin they use if they eat a high-fiber diet.
A clinical study compared people with type 2 diabetes, who were eating 50 g. of fiber daily, with people getting the recommended 24 g. of fiber daily. After 6 weeks, people on the higher-fiber diet had better control of blood glucose, insulin, and blood lipids. In another clinical study, a group of men with type 2 diabetes, who took psyllium twice daily, lowered blood glucose and lipid values compared to a control group taking a placebo.
Clinical studies and human case reports suggest that soluble fiber (such as psyllium, pectin, and guar gum) may make you feel more satisfied, so you eat less and lose weight. Research also suggests that high intakes of dietary fiber may help prevent weight gain in the waist circumference.
Eating more high-fiber foods (such as oatmeal, oat bran, psyllium, and legumes) may help lower heart disease risk.
There are conflicting results from studies examining whether a high-fiber diet can help prevent colon cancer. Some studies suggest fiber protects against the development of colorectal cancer. Most large, well-designed clinical studies, however, show only a small association between how much fiber people eat and their risk of colorectal cancer. In addition, fiber does not seem to protect against the recurrence of colorectal cancer in people who have already been treated for the condition.
Other types of cancer
Preliminary clinical evidence suggests that a diet high in fiber (in conjunction with lifestyle changes and conventional medication) may help protect against certain types of cancer such as prostate, breast, and uterine. More research is needed.
Preliminary evidence suggest that high dietary fiber intake is associated with reduced inflammation and a lower risk of death. These associations are more pronounced among people who have kidney disease.
Soluble fiber is found in dried beans and peas, oats, barley, legumes, fruits, flax, and psyllium seed husks.
Insoluble fiber is found primarily in fruits and vegetables, whole grain products, and wheat and corn bran.
Fiber is available as a supplement in several forms, including fiber tablets, capsules, and powders. Fiber is also available as bulk fiber laxatives, including psyllium.
How to Take It
The following are daily fiber recommendations from the National Academy of Sciences' Institute of Medicine:
For infants and children under 18 years of age, there is no daily fiber recommendation. Children with specific fiber needs should increase the amount of foods in their diets with fiber that they eat slowly over a period of days. DO NOT give fiber supplements to a child without first asking your doctor or pediatrician.
The National Academy of Nutrition and Dietetics recommends 20 to 35 g. per day from a variety of fiber-rich foods. If you are not getting enough fiber, you may need to add more fiber-rich foods to your diet. Choose whole grain products, raw or cooked fruits and vegetables, dried beans, and dried peas. Refined or processed foods, including fruit juices, white breads, pastas, rice, and non whole grain cereals, are lower in fiber. The grain refining process removes the outer coat (bran) from the grain, which lowers its fiber content. Peeling fruits and vegetables also decreases their fiber content.
Because supplements may have side effects, or interact with medications, you should take them only under the supervision of a knowledgeable health care provider.
In general, fiber supplements may reduce or delay your body's absorption of certain medications. Try to take medications at least 1 hour before or 2 to 4 hours after taking fiber.
You should always drink an 8 oz. glass of water with fiber supplements. It is also important to drink at least 6 to 8 full glasses of water throughout the day to avoid constipation. Taking fiber supplements without enough water may cause the supplement to swell and could cause choking. DO NOT take this product if you have difficulty swallowing. People with esophageal stricture (narrowing of the esophagus), or any other narrowing or obstruction of the gastrointestinal tract should not take fiber supplements.
If you have chest pain, vomiting, or difficulty swallowing or breathing after taking fiber supplements, seek immediate medical attention.
Fiber can cause gas and bloating.
If you have impacted stool, which is a complication of constipation, DO NOT take fiber supplements without first seeking the approval of your doctor.
It is rare, but people who take soluble fiber supplements for a long time may develop allergic reactions (even anaphylaxis).
If you are currently being treated with any of the following medications, you should not take fiber supplements without first talking to your doctor.
Antidepressant medications (tricyclic antidepressants): Dietary fiber may lower the blood levels and effectiveness of tricyclic antidepressant medications. If you take tricyclic medications, talk to your doctor before taking fiber supplements or adding more fiber to your diet. Tricyclic antidepressants include:
- Amitriptyline (Elavil)
- Doxepin (Sinequan)
- Imipramine (Tofranil)
Diabetes medications: Fiber supplements may help regulate blood sugar levels. But they can also reduce the absorption of some medications, such as glyburide (Diabeta) and metformin (Glucophage). Talk to your doctor before taking fiber supplements if you have diabetes. DO NOT take fiber supplements at the same time as your medications. Wait a few hours in between.
Carbamazepine: Taking soluble fiber such as psyllium with carbamazepine (Tegretol), a medication used to treat seizures, may decrease the absorption and effectiveness of carbamazepine. A doctor should monitor blood levels of anyone taking both soluble fiber and carbamazepine.
Cholesterol-lowering medications: Combining psyllium or other soluble fibers with cholesterol-lowering medications (known as bile acid sequestrants) may help lower cholesterol levels. If you take these medications, talk to your doctor to see whether psyllium is safe and right for you. These drugs include:
- Cholestyramine (Questran)
- Colestipol (Colestid)
One study found that when people taking simvastatin (Zocor) added psyllium supplements to their regimen, they lowered cholesterol levels as much as if they had been taking a double dose of simvastatin.
Digoxin: Fiber supplements may reduce the body's ability to absorb digoxin (Lanoxin), a medication used to regulate heart function. DO NOT take fiber supplements at the same time as digoxin.
Lithium: Clinical reports suggest that psyllium or other soluble fibers may lower lithium levels in the blood, making lithium less effective. Lithium levels should be monitored very closely by a doctor, especially if there is a big change in fiber intake.
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Steven D. Ehrlich, NMD, Solutions Acupuncture, a private practice specializing in complementary and alternative medicine, Phoenix, AZ. Review provided by VeriMed Healthcare Network. Also reviewed by the A.D.A.M Editorial team.