The Interaction of Dietary Fibers and Cholesterol upon the Plasma Lipids and Lipoproteins, Sterol Balance, and Bowel Function in Human Subjects

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Abstract
To identify any metabolic effects of dietary fiber upon cholesterol metabolism in man, six adult volunteer subjects were fed eucaloric cholesterol-free formula diets, with and without added dietary fiber for two 4-wk periods. A large quantity of dietary fiber was fed, some 60 g of plant cell wall material (or 16 g of crude fiber) derived from corn, beans, bran, pectin, and purified cellulose. This provided about five times the fiber intake of the typical American diet. The addition of fiber to the cholesterol-free diet did not change either the plasma cholesterol level (171±21 mg/dl, SEM, to 167±18) or the triglyceride (103±39 to 93±27 mg/dl). The excretion of both endogenous neutral steroids and bile acids were unchanged with fiber (505±41 to 636±75 mg/day and 194±23 to 266±47 mg/day, respectively.) However, total fecal steroid excretion was increased 699±29 to 902±64 mg/day, P < 0.025). With fiber, intestinal transit time was decreased (59±9 to 35±8 h, P < 0.005), and both the wet and dry stool weights were greatly increased. A second group of six subjects was fed similar diets containing 1,000 mg cholesterol derived from egg yolk. The addition of fiber to the 1,000-mg cholesterol diet did not alter either plasma cholesterol level (233±26 to 223±36 mg/dl) or triglyceride (102±19 to 83±11 mg/dl). The excretion of endogenous neutral steroids (618±84 to 571±59 mg/day), of bile acids (423±122 to 401±89 mg/day), and of total fecal steroids (1,041±175 to 972±111 mg/day) were unchanged by fiber. The absorption of dietary cholesterol was not altered when fiber was added to the 1,000-mg cholesterol diet (44.0±3.3 to 42.9±2.5%). A two-way analysis of variance utilizing both groups of subjects indicated a significant (P < 0.001) effect of dietary cholesterol upon the plasma cholesterol concentration. We concluded that a large quantity of dietary fiber from diverse sources had little or no effect upon the plasma lipids and sterol balance in man in spite of the fact that intestinal transit time and stool bulk changed greatly.