Dietary fat and cholesterol metabolism in adult rats undergoing rapid tissue repletion.

An experimental model in which adult rats underwent rapid rates of tissue repletion after dietary restriction served to explore the influence of dietary fat on cholesterol metabolism. Adult rats severely restricted in protein and energy were refed either 8 or 24 hours per day for 10 days. Refeeding diets contained approximately 0% or 20% fat by weight as safflower oil or beef tallow and 4% or 17% protein on an energy basis. Concentration or source of dietary fat did not significantly influence either serum or hepatic cholesterol concentrations. Inclusion of dietary fat increased incorporation of 3H-acetate into digitonin precipitable sterols although type of fat did not influence this parameter. Specific activities of serum and hepatic cholesterol were identical for rats fed with diets containing safflower oil and beef tallow, but an elevation in acidic 14C-steroid excretion per g diet consumed occurred with safflower oil as compared with beef tallow. The data suggest that, in the absence of exogenous cholesterol, high levels of polyunsaturated fat may influence cholesterol metabolism primarily by increasing synthesis and excretion of bile acids.