Effect of varying type and quantity of dietary fat on the fecal excretion of bile acids in humans subsisting on formula diets

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.

Section: Methodssupporting

confidence: 52%

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

Avigan¹,

Steinberg²

1965

“…Early reports of augmented fecal excretion of bile acids in man (26)(27)(28)(29)(30)(31), of nonacidic or neutral sterols in man (31,32), the rat (9,33,34), and the rabbit (35), or of both bile acids and neutral sterols in man (36)(37)(38) and the rat (19,(39)(40)(41) agreed that an increased fecal excretion of cholesterol accompanied the hypocholesteremic effect of substituting polyunsaturated for saturated fatty acids in the diet. Hellman, Rosenfeld, Insull, and Ahrens (42) suggested that this increase fecal loss accounted for the fate of the cholesterol leaving the plasma under these conditions.…”

Section: Introductionmentioning

confidence: 99%

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

Moore¹,

Anderson²,

Taylor³

et al. 1968

134

Fecal bile acid and neutral sterol excretion rates were determined in five healthy young men when serum cholesterol changes were induced by isocaloric substitution of an unsaturated (safflower oil) for a saturated fat (butter). The isotope balance method was used after the intravenous injection of cholesterol-4-14C. A feces extraction method is presented which permits essentially complete separation of fecal neutral sterols and bile acids.There was a significant increase in the total excretion of the fecal end products of cholesterol metabolism from 966 + 42 mg/day on saturated fat to 1147 + 45 mg/day on unsaturated fat, and the increase was equally distributed between the neutral sterol and bile acid fractions. With the substitution of dietary fats, regardless of the sequence of their feeding, there was a 28% reduction in serum cholesterol concentration during ingestion of the unsaturated fat. There were reciprocal changes in serum cholesterol levels and fecal steroid excretion with the substitution of one type of fat for the other. The changes in plasma cholesterol content were more than adequately balanced by the reciprocal changes in fecal cholesterol end product excretion.The findings in this study agree with several previous reports in supporting the hypothesis that the hypocholesteremic action of dietary unsaturated fatty acids is associated with an increase in the fecal loss of bile acids and neutral sterols.

“…Aliquots of the stool and urine samples were analyzed for nitrogen by a macroKj eldahl procedure. The stool samples were also analyzed for bile acids (27) and total sterols (22). Table III presents data on body weight, nitrogen balance, and total serum proteins, as mean values for the seven subjects unless otherwise noted.…”

Section: Experimental Methodsmentioning

confidence: 99%

The Influence of Dietary Protein on Plasma Lipids in Human Subjects

Leveille¹,

Sauberlich²,

Powell³

et al. 1962

Most studies concerning the influence of dietary protein on serum or plasma lipids have been conducted with experimental animals. A hypocholesterolemic effect has been demonstrated for high dietary protein levels in growing swine, rats, and chicks (1-6). In the rat a hypercholesterolemic diet, containing cholesterol, or cholic acid, or both, is required to demonstrate a substantial depressant effect of high protein on cholesterol; however, this effect has been demonstrated in swine and chicks fed essentially cholesterol-free diets (1,3,4). Certain studies have indicated that the hypercholesterolemic effect of low protein is primarily the result of a sulfur amino acid deficiency; Cebus monkeys (7) and rats (8, 9), receiving diets adequate in choline but deficient in sulfur amino acids, develop a hypercholesterolemia that can be overcome by the addition of methionine to the diets. It has been further demonstrated that the serum cholesterol depression resulting from methionine supplementation of a deficient diet is independent of the growth response observed (8, 10) in growing animals.Methionine supplements appear to function differently in choline-deficient rats. Rats fed diets deficient in choline and sulfur amino acids have shown lowered serum cholesterol and elevated liver cholesterol levels; dietary supplementation of either sulfur-containing amino acids, or choline, or both to such animals results in a return of serum and liver cholesterol values to normal levels (11,12). This hypocholesterolemia resulting from a choline deficiency has not been observed in the chick (6), probably owing to the lack of a lipotropic effect of choline in this species as compared with the rat (13 (15), however, noted that the serum cholesterol levels of elderly patients frequently were elevated by increased protein intakes. Olson (16) fed diets supplying 100 g of protein per day followed by isocaloric, iso-fat diets supplying 25 g of protein per day to 9 subjects. The lower serum cholesterol levels observed during the low protein intake were attributed to a low dietary level of choline and sulfur-containing amino acids. In a more recent study Walker, Morse and Overley (17) fed two groups of young female subjects diets supplying 45 to 50 g of protein per day from animal or vegetable sources. The serum cholesterol level decreased in both groups but more so in the group receiving vegetable protein.In view of the existing controversy concerning the influence of dietary protein on serum lipids in man, the present study was initiated. The results reported were obtained in a carefully controlled study employing young male volunteers as subjects. EXPERIMENTAL METHODSThe subjects for this study were 7 healthy, young, male volunteers, whose average age was 21.6 years (range, 19 to 23). Their average initial weight was 77.4 kg (range, 70.2 to 97.5). The subjects were housed in a metabolic ward and were permitted off the ward for supervised activity. Body temperature, blood pressure, and body weight were recorded daily for each man.The study ...