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 l evels of 18:0 and distinct triacylglycerol (TAG) profiles. Male Spragu e-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, a nd then killed in a fasted or fed state. Chylomicron (CM) fatty acid p rofiles suggested reduced absorption of 18:0 with greater 18:0 intake. CM TAG profiles indicated a reduction or loss of two TAG species comp ared to the TAG profiles of the stearate-rich diets: 1-palmitoyl-2-ole oyl-3-stearoyl glycerol (POS) and 1,3-distearoyl-2-oleoyl glycerol (SO S). 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-den sity lipoprotein esterified/free cholesterol than all other groups. He patic stearoyl-CoA and oleoyl-CoA concentrations, the substrate and pr oduct for hepatic DELTA9 desaturase, were not significantly different for corn oil-fed and cocoa butter-fed groups in spite of a large diffe rence in 18:0 intake. These data suggest that the neutral or cholester ol-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.