Relationship between changes in plasma lipoprotein concentrations and fecal steroid excretion in man during consumption of four experimental diets.

Limited information is available on the mechanism by which changes in nutrient intake influence plasma lipids. We compared the effects on plasma lipoprotein levels of 3 dietary modifications involving changes in total fat intake (27-40% of calories), cholesterol intake (100-250 mg/1000 kcal), the dietary polyunsaturated to saturated fatty acid ratio (0.3-1.0) and intake of vegetable-derived fiber and protein. On these 3 diets, plasma low density lipoprotein was reduced by 26-34%. Fecal bile acid excretion was similar on all diets (363-379 mg/day). There was no alteration in fecal bile acid output associated with an increase in polyunsaturated or total fat intake. Sterol balance became significantly more negative during consumption of only 1 of the 3 cholesterol-lowering diets. The observed reduction in plasma cholesterol levels was not associated with an increase in fecal bile acid output suggesting that diet-induced changes in circulating cholesterol are not maintained by an increase in sterol turnover but may reflect alterations in hepatic cholesterol and lipoprotein synthesis.