Effects of dietary triglycerides on serum and liver lipids and sterol excretion of rats.
The effects of several highly purified simple and mixed dietary triglycerides (TGs) on serum and liver cholesterol and on sterol excretion were studied in rats. The TGs contained 4- to 18-carbon fatty acids with melting points of -75 to 63.5 degrees C. Ratios of polyunsaturated to saturated fatty acids ranged from 0.1 to 105. Ratios of total unsaturated to saturated fatty acids ranged from 0.1 to 115. All diets contained 8% TG plus 0.82% safflower oil. Sterols were quantified directly by a new and improved high resolution gas chromatographic method and were identified by mass spectrometry. TG digestibilities correlated negatively with melting points above 30 degrees C (R = -0.9). Serum cholesterol was lower in rats fed tributyrin, tricaproin, tricaprylin, tricaprin, trielaidin, trilinolein or partially hydrogenated soybean oil (43-49 mg/dl) than in those fed trilaurin, trimyristin, tripalmitin, tristearin, triolein or corn oil (54-59 mg/dl). Liver lipid levels correlated (R = 0.65) with the degree of unsaturation of dietary TGs. Liver cholesterol levels correlated negatively with fecal excretion of coprostanol plus cholesterol (R = -0.4). Coprostanol plus cholesterol excreted in feces correlated weakly (R = 0.3) with intake of total sterol and of polyunsaturated TGs (R greater than or equal to 0.4 are at least 80% significant). The results demonstrate that consumption of polyunsaturated TGs was associated with higher hepatic lipid levels. Also, greater fecal excretion of coprostanol plus cholesterol was associated with lower hepatic cholesterol levels.