Reduced digestibility of beef tallow and cocoa butter affects bile acid excretion and reduces hepatic esterified cholesterol in rats.

We investigated stearic acid (18:0) digestibility and how it affects bile acid excretion in male Sprague-Dawley rats fed diets containing (g 18:0/ 100 g fatty acids): pork lard (13); beef tallow (19); cocoa butter (35); corn oil (2) or corn oil plus cholestyramine for 25 d. Apparent lipid digestibility was reduced with increased dietary intake of 18:0 as follows: lard (90%), beef tallow (82%), cocoa butter (78%), cholestyramine (87%), and corn oil (94%); P < 0.001, pooled SD = 2. Hepatic concentrations of total and esterified cholesterol were significantly less in cocoa butter-, beef tallow- and cholestyramine-fed groups compared with lard- and corn oil-fed groups. Fecal bile acid excretion was significantly greater in rats fed cocoa butter or cholestyramine compared with those fed corn oil. The half-life of intraperitoneally administered 14C-cholic acid was significantly longer in rats fed cocoa butter (1.36 +/- 0.02 d) compared with cholestyramine (0.98 +/- 0.03 d) and intermediate in those fed corn oil, lard or beef tallow (1.11-1.21 +/- 0.05 d). Fecal excretion of muricholic acids (bile acids) correlated strongly with dietary intake of 18:0 (r2 = 0.98, P < 0.01), whereas excretion of bile acids derived from cholic and chenodeoxycholic acids was similar among groups. In summary, the lower digestibility of cocoa butter is associated with increased fecal bile acid excretion, reduced hepatic concentration of esterified cholesterol, decreased fractional turnover of 14C-cholic acid and increased excretion of muricholic acids in rats. The mechanism by which stearate-rich dietary fats alter bile acid and cholesterol metabolism is, however, uncertain.

Alteration of plasma lipids in the rat by fractionation of modified milk fat (butterfat).

Our objective was to determine the nutritional effects of defined fat fractions of modified milk fat, or butterfat (anhydrous butter without the milk fat globule membrane) on lipid and lipoprotein cholesterol concentrations in plasma of rats fed diets containing 16% fat and two amounts of cholesterol. Five dietary fats were compared: 1) intact butterfat, 2) a liquid butterfat fraction enriched in oleic acid and unsaturated triacylglycerols with < 40 carbon atoms, 3) a solid butterfat fraction enriched in palmitic and stearic acids, 4) corn oil, and 5) palm oil. The extent of diet-induced hypercholesterolemia was the greatest with palm oil, followed by solid butterfat, corn oil, intact butterfat, and the lowest with liquid butterfat. Triacylglycerol concentrations in plasma were greater for rats fed palm oil than for those fed corn oil or liquid or intact butterfat. Among the high cholesterol dietary groups, ingestion of the liquid butterfat diet resulted in similar lipoprotein cholesterol and very low density lipoprotein concentrations relative to the corn oil diet, and ingestion of the solid butterfat diet resulted in similar lipoprotein cholesterol and very low density lipoprotein concentrations relative to the palm oil diet. These results suggest that changes in the triacylglycerol and fatty acid composition of butterfat by fractionation processes may improve its nutritional profile.

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.