Fiber is an important part of good nutrition. A diet high in fiber will contain fruits, vegetables, legumes, and whole and highfiber grain products. Many of these foods are rich in micronutrients and nonnutritive ingredients (eg, antioxidants, phytoestrogens), but at the same time they offer a food source that is low in calories and fat and high in volume. Such characteristics make these foods potentially useful in the treatment and prevention of obesity, cardiovascular disease, diabetes, and constipation, especially when combined with adequate fluid intake.1
Americans are not getting enough fiber, however. The average dietary intake of fiber in the United States is estimated to be 14 to 15 g/day, whereas the recommended amount for an adult is 20 to 35 g/day, or 10 to 13 g/1000 kcal.1
Negative Consequences of a Diet Low in Fiber
Without adequate dietary fiber intake, a person may become constipated or develop other health complications (eg, elevated blood cholesterol).1,2-5 The consequences of constipation include fecal incontinence, hemorrhoids (especially during pregnancy), and fecal impaction.2,6 A common method used for the treatment of constipation caused by slow-transit or constipation-predominant irritable bowel syndrome is the use of a high-fiber diet or a fiber product, but adding fiber does not work for all patients.4,5 In fact, increased fiber intake may be a problem for some patients with idiopathic constipation, so pharmacists should use caution in recommending increased fiber intake in patients with chronic constipation.7
Low-fiber diets can also increase the incidence of diverticulosis. It is thought that chronic insufficient bulk causes the gut to contract more to propel the smaller mass through the intestinal tract. The chronic increase in force may lead to the development of the diverticula by causing herniations of the mucosal layer of the colon musculature in areas that are weak (eg, areas around blood vessels). By increasing the fecal mass, the pressure in the gut lumen can be decreased, and the chance of developing new diverticula or worsening existing diverticula is decreased.1
Important Health Benefits of High-Fiber Diets
Fiber may have health-protective benefits. Micronutrients, including antioxidants, are found in foods high in fiber. These can reduce the risk of cardiovascular diseases, eg, hypertension14 and dyslipidemia.1,8-12 Examples of food that are able to lower blood cholesterol are barley, legumes, fruits and vegetables, oatmeal, oat bran, psyllium husk, and rice hulls.1,11 The mechanism for this effect appears to be the increase in viscosity of the gut and interference with bile acid absorption from the ileum,1 a mechanism similar to that with cholestyramine and colestipol.13
Fiber also shows potential benefit in obesity and diabetes. Its potential benefit in the treatment or prevention of obesity is probably related to its ability to increase satiety and lower overall caloric ingestion. Foods high in fiber are generally less energy-dense and larger in volume. These foods take longer to eat, and their presence in the gut creates a feeling of satiety sooner. The breakdown by acid and intestinal enzymes also takes longer, resulting in lower postprandial blood glucose and insulin concentrations, especially in patients with diabetes. Long-term ingestion of higher fiber diets can improve glycemic control.1,15
Thus, it can be seen that health benefits may be associated with increasing the amount of fiber in the diet. Many people, however, are unable or unwilling to increase the fiber content in their diet to achieve the recommended 20 to 35 g/day, especially those who are eating a low-carbohydrate diet. In these individuals, it may be necessary to use an alternative source of fiber, such as fiber supplements.
Fiber products vary in the amount and type of fiber (Table). Factors such as source of fiber, amount of fiber, dosage, flavor and variety, and cost can influence patient compliance. Fibers are generally characterized as soluble or insoluble. A soluble fiber (eg, inulin, hydrolyzed guar gum) dissolves in water and is metabolized in the intestinal tract to short-chain fatty acids, stimulates the growth of local flora, and increases the water-holding capacity of the colonic content and fecal moisture. In contrast, insoluble fiber (eg, psyllium, methylcellulose) is not extensively metabolized and mechanically increases fecal mass by water retention.22 Both forms of fiber are capable of decreasing transit time and improving defecation but may not produce the same benefits for all medical conditions.22
Hydrolyzed guar gum (eg, Benefiber) is a vegetal, water-soluble, nonviscous, nongelling dietary fiber derived from guar gum. The recommended dose for Benefiber is 1 to 3 tablets or 1 to 2 tablespoons of powder.13,22 Methylcellulose products (eg, Citrucel) are a soluble fiber derived from plant sources. The recommended dose of Citrucel is 2 caplets each day or 1 tablespoon of powder. Psyllium husk (eg, Metamucil) and psyllium hydrophilic mucilloid (eg, Fiberall) are soluble fibers and are partially fermented.The recommended dose of Metamucil is 2 to 6 capsules or 1 tablespoon of powder each day. The recommended dose of Fiberall powder is 1 tablespoon per day. Inulin (eg, FiberChoice) is a fiber that occurs naturally in fruits, vegetables, and grains. The recommended dose of FiberChoice is 2 tablets to achieve 4 g/day,13 which can be easier and more convenient than some of the other fiber products.
Good nutrition involves getting enough fiber every day, and this is a problem for most Americans. Fiber supplements are one way to achieve the recommended amounts of fiber, but even with these convenient options, compliance can be an issue. Thus, available fiber products offer a variety of dosage forms and flavors. Some patients will like the option to take a chewable tablet, capsule, or caplet over powders that need to be mixed with water or food. The pharmacist can summarize these options to the patient and offer suggestions that might ensure regular compliance with a fiber supplement and adequate fiber intake.
Dr. Baker is professor of pharmacotherapy and director of the Drug Information Center at Washington State University College of Pharmacy.
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