Dietary Fiber and its use to lower

cholesterol

by James Nuovo

Use of Dietary Fiber to Lower Cholesterol Dietary water-soluble fiber may be a key factor in the management of hypercholesterolemia. Food items that are rich in this type of fiber are common and are easy to incorporate into a patient's diet. The lipid-lowering effect is dose-related. Consumption of an adequate amount of water-soluble fiber each day may reduce cholesterol levels by 10 to 20 percent. The National Cholesterol Education Program(1) recently published specific guidelines for the management of hypercholesterolemia, a problem commonly encountered by family physicians. Unfortunately, dietary modification, the first step in lowering cholesterol levels, often is not successful. When diet therapy fails, lipid-lowering agents, such as cholestyramine (Questran) and lovastatin (Mevacor), are usually recommended. These drugs are expensive and are associated with a significant number of side effects.(2) It would be preferable to have a lipid-lowering agent that is nontoxic, inexpensive and easy to incorporate into a patient's diet. Dietary water-soluble fiber may be this agent.(3)

Types of Fiber

Fiber, a diverse substance that resists digestion in the gastrointestinal tract, is found in all plants. Common types of fiber include cellulose, lignin, pectin, gum and mucilage.(4)

Cellulose is found in the cell walls of all plants, and lignin is the primary component of wood. Wheat bran is a rich dietary source of both cellulose and lignin.(5) Pectin is found in many fruits and vegetables and is particularly concentrated in the peel of citrus fruits. Pectin concentrate is used in making jams and jellies.

Different types of gum, the sticky material extruded at the site of plant injury, are used in the food industry as emulsifiers, thickeners and stabilizers. A small amount of guar gum, a bean extract with water-binding and stabilizing properties, is commonly added to sauces, dressings, ice cream and frozen foods. Mucilage, the viscid principle in plants (consisting of a gum dissolved in the juices of the plant), is the major component of the bulk laxatives produced by pharmaceutical companies. Psyllium, a mucilage derived from a seed, is the primary ingredient in the commercial preparations Metamucil and Fiberall.

Fibers also may be categorized in terms of water solubility. Water-soluble fibers, including pectin, gums and mucilages, have a well-documented lipid-lowering effect.(3) Nonwater-soluble fibers, such as cellulose and lignin, have virtually no effect on serum lipids.(7)

How Fiber Lowers Lipids

The effect of dietary fibers on bile acid absorption is similar to that of the bile acid-binding resins.(3,4,7) Dietary fibers have been shown to bind bile acids in vitro.(7) The binding and removal of bile acids inhibit the formation of micelles, which are essential for the absorption of cholesterol and other lipids from dietary and biliary sources. The prevention of bile acid resorption disrupts enterohepatic circulation and affects the total body bile salt pool. This results in increased hepatic conversion of cholesterol into newly synthesized bile acids, thereby decreasing serum cholesterol.

Summary of Studies on Fiber

A number of studies have examined the lipid-lowering effects of various types of fiber.(3,4,7,8) Most of these studies have focused on purified fiber products (pectin and psyllium) or on foods with a naturally high concentration of fiber (oat bran and beans). Kay and Truswell(7) reviewed 11 studies on pectin administered in capsule form or in fruit jelly. The dose ranged from 6 to 40 g per day. In the studies in which subjects received at least 20 g of pectin per day, serum total cholesterol levels were reduced by 12 to 15 percent.

Anderson and colleagues(8) recently studied the lipid-lowering effects of psyllium in 26 men with mild to moderate hypercholesterolemia. The subjects were given 3.4 g (1 teaspoon) of psyllium three times a day in a double-blind, placebo-controlled study. Their usual diet was not changed significantly. After eight weeks of treatment with psyllium, serum total cholesterol levels decreased by 14.8 percent and low-density lipoprotein (LDL) cholesterol levels decreased by 20.2 percent.

Of the studies performed on fiber-rich foods, the most promising have been those done on oats and beans. Oat bran, a rich source of water-soluble dietary fiber, contains approximately twice as much fiber as rolled oats (oatmeal).(6) Gold and Davidson(9) studied 72 subjects who were given a relatively low dose of oat bran (17 g per day). Following 28 days of treatment with oat bran, serum total cholesterol levels were reduced by 5.3 percent, and LDL cholesterol levels were reduced by 8.7 percent.

After reviewing seven other studies on oat products, Gold and Davidson(9) formulated an equation to determine the percent decrease in cholesterol that could be expected from a given dose of oat bran: percent decrease in cholesterol = 0.156 x g of oat bran per day + 1.0. Therefore, achievement of a 10 to 20 percent decrease in cholesterol would require the consumption of two-thirds cup to one and one-half cups of oat bran (dry weight) per day.

The lipid-lowering effect of bean products is comparable to that of oat bran.(4) In a study by Anderson and associates,(10) 20 men with hypercholesterolemia were randomly allocated 100 g of oat bran or 115 g (4 oz) of pinto and navy beans per day. After 21 days, an average reduction of 19 percent in total serum cholesterol levels occurred in both the oat bran and bean groups; LDL cholesterol levels for the oat bran and bean groups were reduced by 23 percent and 24 percent, respectively.

Dietary Fiber and Lipid-Lowering Drugs

Dietary fiber is as effective as many lipid-lowering drugs in the treatment of hypercholesterolemia.(9)

Cost is an important consideration. Kinosian and Eisenberg(11) recently calculated the cost per year of life saved for treatment with cholestyramine, colestipol (Colestid) and oat bran in individuals with significantly elevated total serum cholesterol levels (greater than 265 mg per dL [greater than 6.85 mmol per L]). Important factors included the direct cost of each intervention, the medical costs that would have been required to care for the averted events (e.g., myocardial infarction, coronary artery bypass surgery, new angina) and the expected years of life gained by the treatment of hypercholesterolemia. According to Kinosian and Eisenberg's calculations, the costs of treatment in terms of years of life saved were as follows: cholestyramine, $117,400; colestipol, $70,900; oat bran, $17,800. The implication is that a broad public health approach to lowering cholesterol by increasing the consumption of water-soluble fiber may be preferable to a medically oriented campaign focused on drug treatment.

Clinical Application

Patients should first be made aware of the dietary recommendations published in the National Cholesterol Education Program's Step One Diet.(1) They also need to be aware of the importance of making simple changes in their choice of snacks, desserts and cooking methods, as well as their selection of foods when dining out. Next, patients need to know how to incorporate fiber into their diets. To this end, they must understand the following principles: (1) only certain types of fiber have lipid-lowering effects; (2) certain foods are naturally rich in water-soluble fiber, and (3) the lipid-lowering effect of fiber is dose-related.

Oat bran has recently received much attention as a means of lowering cholesterol levels. Oat bran may be consumed as cooked hot cereal, muffins and bread, or it may be sprinkled on other foods. This type of fiber is usually well tolerated. The most common problem is finding a way to consume enough oat bran each day to lower cholesterol. Oat bran muffins, which may be eaten for breakfast and for snacks, offer a practical solution to this problem.

Patients also may choose other sources of water-soluble dietary fiber, particularly bean products. Studies show that a combination of two different water-soluble fibers is effective. For example, Anderson and associates(12) demonstrated a 29 percent reduction in LDL cholesterol levels among patients who supplemented their diets with both oat bran and beans.

Final Comment

The lipid-lowering effect of water-soluble fiber is dose-related. When an adequate amount of water-soluble fiber is consumed each day, a 10 to 20 percent reduction in cholesterol may be expected. A reasonable initial approach for a patient with hypercholesterolemia would be to follow the National Cholesterol Education Program's Step One Diet and increase daily consumption of water-soluble dietary fiber. This approach may result in a palatable, effective and less expensive treatment program for a large number of patients with hypercholesterolemia. REFERENCES (1)Report of the National Cholesterol Education Program expert panel on detection, evaluation, and treatment of high blood cholesterol in adults. Arch Intern Med 1988;148:36-69. (2)Lavie CJ, Gau GT, Squires RW, Kottke BA. Management of lipids in primary and secondary prevention of cardiovascular diseases. Mayo Clin Proc 1988;63:605-21. (3)Anderson JW, Tietyen-Clark J. Dietary fiber: hyperlipidemia, hypertension, and coronary heart disease. Am J Gastroenterol 1986;81:907-19. (4)Anderson JW, Chen WJ. Plant fiber. Carbohydrate and lipid metabolism. Am J Clin Nutr 1979;32:346-63. (5)Southgate DA, Bailey B, Collinson E, Walker AF. A guide to calculating intakes of dietary fibre. J Hum Nutr 1976;30:303-13. (6)Chen WJ, Anderson JW. Soluble and insoluble plant fiber in selected cereals and vegetables. Am J Clin Nutr 1981;34:1077-82. (7)Kay RM, Truswell AS. Dietary fiber: effects on plasma and biliary lipids in man. In: Spiller GA, Kay RM, eds. Medical aspects of dietary fiber. New York: Plenum, 1980:153-73. (8)Anderson JW, Zettwoch N, Feldman T, Tietyen-Clark J, Oeltgen P, Bishop CW. Cholesterol-lowering effects of psyllium hydrophilic mucilloid for hypercholesterolemic men. Arch Intern Med 1988;148:292-6. (9)Gold KV, Davidson DM. Oat bran as a cholesterol-reducing dietary adjunct in a young, healthy population. West J Med 1988;148:299-302. (10)Anderson JW, Story L, Sieling B, Chen WJ, Petro MS, Story J. Hypocholesterolemic effects of oat-bran or bean intake for hypercholesterolemic men. Am J Clin Nutr 1984;40:1146-55. (11)Kinosian BP, Eisenberg JM. Cutting into cholesterol. Cost-effective alternatives for treating hypercholesterolemia. JAMA 1988;259:2249-54. (12)Anderson JW, Story L, Sieling B, et al. Hypocholesterolemic effects of high-fibre diets rich in water-soluble plant fibres. J Can Diet Assoc 1984;45:140-9.

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