Interrelationship of stearic acid content and triacylglycerol composition of lard, beef tallow and cocoa butter in rats.

We investigated modes whereby stearic acid (18:0) exerts a neutral or cholesterol-lowering effect using dietary fats which provided graded levels of 18:0 and distinct triacylglycerol (TAG) profiles. Male Sprague-Dawley rats (150-175 g) were fed diets containing 0.2% cholesterol and 16% fat from corn oil, or from 1% corn oil plus 15% lard (13.2% 18:0), beef tallow (19.2% 18:0) or cocoa butter (34.7% 18:0) for 3 wk, and then killed in a fasted or fed state. Chylomicron (CM) fatty acid profiles suggested reduced absorption of 18:0 with greater 18:0 intake. CM TAG profiles indicated a reduction or loss of two TAG species compared to the TAG profiles of the stearate-rich diets: 1-palmitoyl-2-oleoyl-3-stearoyl glycerol (POS) and 1,3-distearoyl-2-oleoyl glycerol (SOS). Hepatic total cholesterol concentrations were 54-77% lower (P < 0.01) in the cocoa butter-fed than the lard-and beef tallow-fed groups. The cocoa butter group showed a significantly lower ratio of high-density lipoprotein esterified/free cholesterol than all other groups. Hepatic stearoyl-CoA and oleoyl-CoA concentrations, the substrate and product for hepatic delta 9 desaturase, were not significantly different for corn oil-fed and cocoa butter-fed groups in spite of a large difference in 18:0 intake. These data suggest that the neutral or cholesterol-lowering effect of 18:0 is not due to hepatic conversion of stearic to oleic acid, and that POS and SOS are poorly absorbed from stearate-rich dietary fats.