Abstract
Although dietary fatty acid saturation is an effective modulator of plasma cholesterol, its effects on bile acid metabolism are not well elucidated. In fact, it is possible that primary changes in bile acid metabolism account for the response in plasma lipids. Thus, the aim of this study was to compare the effect of a diet rich in specific saturated fatty acids [lauric and myristic acid (12:0 + 14:0)] with a diet containing a specific unsaturate, linoleic acid (18:2n6) on factors affecting bile acid metabolism in gerbils. Gerbils were fed a high-fat diet (40% of energy) based on either coconut oil (12:0 + 14:0-rich) or safflower oil (18:2n6-rich). After 4 weeks, plasma sterols, the gallbladder bile acid profile, and fecal bile acid excretion were analyzed along with hepatic concentrations of taurine and cholesterol. Hepatic activities of acyl-CoA cholesterol acyltransferase (ACAT) and cholesterol 7α-hydroxylase were also measured. Exchange of 29% energy as 18:2n6 for 12:0 + 14:0 increased the proportion of saturated and monounsaturated fatty acids at the expense of polyunsaturated fatty acids in plasma, hepatic microsomal membranes, and bile phospholipids. Concentrations of plasma cholesterol and 27-hydroxycholesterol were greatly increased by the 12:0 + 14:0-rich diet. This effect was coupled with significant decreases in hepatic taurine concentration and the activities of ACAT and cholesterol 7α-hydroxylase, as well as fecal bile acid excretion. Analysis of gallbladder bile acids revealed that the 12:0 + 14:0-rich diet decreased the cholate:chenodeoxycholate and primary:secondary bile acid ratios as well as the ratio of taurine:glycine conjugates. In essence, the exchange of dietary lauric and myristic acids for linoleic acid was associated with decreased production and excretion of bile acids concurrent with reduced hepatic taurine and taurine-conjugated bile acids.