Dietary cholesterol and type of fat differentially affect cholesterol metabolism and atherosclerosis in baboons

This study was designed to determine the differences in cholesterol metabolism due to dietary cholesterol and type of fat in adult baboons. From weaning at 16 wk to 7-8 y of age, 80 baboons were fed one of four diets: high cholesterol (0.24 mg/kJ) or low cholesterol (0.0024 mg/kJ) with 40% of energy from saturated fat [polyunsaturated/saturated fatty acid ratio (P/S) = 0.37] or unsaturated fat (P/S = 2.1). High cholesterol and saturated fat independently raised serum lipoprotein and apolipoprotein concentrations to about the same extent. The liver cholesterol concentration of baboons fed high cholesterol diets was 23% higher than that of baboons fed low cholesterol. High dietary cholesterol also increased bile cholesterol concentration by 25%, the neutral steroid excretion rate by 66% and the bile acid excretion rate by 30%. With feeding of saturated fat, compared with unsaturated fat, liver cholesterol was 24% lower, bile cholesterol 26% lower and the neutral steroid excretion rate 12% lower. Dietary cholesterol greatly suppressed whole-body cholesterol synthesis, but type of fat did not affect cholesterol synthesis rate. These results suggest that dietary cholesterol and saturated fat increase plasma lipoprotein concentrations through different physiological mechanisms.