Sterol and bile acid excretion in man and the effects of dietary fat.

Abstract

It is now well established that diets rich in saturated fatty acids lead to high levels of serum cholesterol, whereas diets rich in unsaturated fatty acids tend to be associated with lower levels. The mechanism by which these changes in serum cholesterol are induced by dietary fat is not known. One possible explanation for these effects would be either inhibition of cholesterol biosynthesis by unsaturated fats or stimulation of synthesis by saturated fats. The effects on synthesis, if any, could, in turn, be either the result of a direct action of the dietary fat on the biosynthetic system or of a secondary adjustment to any change in the rate of oxidation and excretion of cholesterol and its metabolites. Alternatively, changes in dietary fat might not affect the turnover rate, but cause a shift of part of the serum cholesterol pool, either from or into tissue compartments.Finally, the changes in serum cholesterol might reflect a primary effect not on sterol metabolism per se, but on the metabolism of lipoproteins, direct or mediated through effects on the metabolism of one or several of the moieties making up the macromolecule. These might act singly or in combination.In the present studies we have administered cholesterol-4-14C to subjects fed liquid formula diets containing saturated or unsaturated fat and subsequently measured the specific radioactivity of plasma cholesterol as a function of time. Simultaneously, the fecal excretion of sterol and bile acid was measured by a radioactivity balance method.

The effects of unsaturated dietary fats on absorption, excretion, synthesis, and distribution of cholesterol in man

“…1 panied by an increased excretion of fecal endogenous neutral steroids as well as of exogenous neutral steroids if the diet contained cholesterol. However, as in several previous studies (12,27,28) in which no change in neutral steroid excretion was found during unsaturated fat feeding, in the present experiments no increase in fecal neutral steroids of endogenous origin was seen in 10 of 11 patients. Furthermore, in five patients in whom reliable measurements of absorption of exogenous cholesterol could be made, the substitution of unsaturated for saturated fat produced no significant decrease in the absorption of dietary cholesterol.…”

Hypocholesterolemia in Clinically Serious Conditions - Review

“…Sterol balance 17 provides a direct measure of endogenous biosynthesis rate expressed as the diff erence between fecal sterol excretion (cholesterol and bile sterols) and cholesterol intake. The necessary presumption is equilibrium of internal sterol pools which can take weeks or months to achieve.…”

Effect of dietary fat on the fecal excretion of cholesterol and its degradation products in man

“…Others have found no significant differences in the turnover rate of biliary cholic acid (56,57), in the excretion of neutral steroids (58), or in the fecal excretion of bile acids and neutral sterols (59,60) in men given saturated or unsaturated fats in the diet. Spritz, Ahrens, and Grundy (60) suggested that, by exclusion, the hypocholesteremic effect of polyunsaturated fat is due to a redistribution of cholesterol from plasma into other body tissues.…”

“…The isotope balance method introduced by Hellman and associates in 1957 (42) is based upon two assumptions: first, that the 4-carbon atom of the cholesterol molecule is not metabolized to any significant extent in the body or in the intestinal lumen (73)(74)(75)(76)(77)(78) and, therefore, the metabolic products of cholesterol metabolism (bile acids and sterols) will contain the "4C label of the administered cholesterol-4-14C; and second, that the fecal end products of cholesterol metabolism have specific activities that closely parallel that of the serum cholesterol (42,50,59,(77)(78)(79)(80)(81)(82).…”