Many well designed clinical studies have shown that fiber relieves constipation. Most clinical studies examined wheat bran and psyllium. Researchers think fiber relieves constipation by adding bulk to stool and helping it move faster through the intestines. Do not take fiber supplements if you have impacted stool, a complication of constipation, without first seeking the approval of your doctor.
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 well designed clinical studies show that soluble fiber helps regulate stool frequency and consistency in people with 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.
Patients with diverticulosis are often given fiber supplements to prevent constipation and stop the condition from progressing. The American Dietetic Association (ADA) recommends 25 - 30 grams of fiber per day; your doctor may recommend more. Some researchers think that people with diverticulosis should avoid foods such as nuts, pumpkin, caraway, and sesame seeds. It is thought that 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, flax seed, 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 (or “bad”) cholesterol levels.
Clinical studies suggest 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 grams of fiber daily with people getting the American Diabetes Association’s recommended 24 grams 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 full and less hungry, so that 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. But most large, better designed clinical studies 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. Further studies are needed to be sure, however.
If you are currently being treated with any of the following medications, you should not use fiber supplements without first talking to your health care provider.
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, and don’t 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 psylium is safe and right for you. These drugs include:
- Cholestyramine (Questran)
- Colestipol (Colestid)
One study also 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 health care provider, especially if there is any big change in fiber intake.
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