The average serum cholesterol level of rats fed a human-type diet that contained 28% (wt/wt) beef fat and 0.5% added cholesterol and that was low in non-digestible constituents was lower than that of rats fed an equivalent diet prepared from purified ingredients, 94 mg/dl and 163 mg/dl, respectively. In order to identify the hypocholesterolemic ingredients in the human-type diet, the sources of protein and carbohydrate in the purified diet, casein and cornstarch, were substituted for the corresponding sources in the human-type diet, beef tenderloin, bread, and rice. These prepared diets were fed to female Sprague-Dawley rats for 10 weeks. Diets containing casein were hypercholesterolemic compared to stock rat diet, but rats fed the bread with the casein had the lowest serum cholesterol level, 112 mg/dl, of any casein diet group. The cholesterolemic response of rats fed the beef and bread diet was the same as that of stock-fed rats, 94 mg/dl and 86 mg/dl, respectively. The level of cholesterol in the liver of rats fed the beef and bread diet was lower than that of rats fed the purified diet, 7.7 mg/g and 28.5 mg/g, respectively, but it was higher than that of rats fed the stock diet, 3.8 mg/g. The hypocholesterolemic effect of beef and bread may be related to reduced cholesterol absorption. These data demonstrate the sensitive control on cholesterol metabolism of nonlipid diet ingredients.