Abstract Within the context of reduced-fat diets, the effects of incorporating a fat high in stearic acid and adding moderate amounts of dietary cholesterol were examined in 14 middle-aged and elderly women and men (range, 46 to 78 years) with low-density lipoprotein cholesterol (LDL-C) concentrations > 130 mg/dL (range, 133 to 219 mg/dL) at screening. The subjects consumed each of the five diets, which were as follows: (1) a baseline diet (35% fat with 13% saturated fatty acids [SFAs], 12% monounsaturated fatty acids [MUFAs], and 8% polyunsaturated fatty acids [PUFAs], and 128 mg cholesterol/1000 kcal); (2) a reduced-fat diet, in which two thirds of the fat was provided as corn oil (com oil-enriched diet: 29% fat with 7% SFAs, 9% MUFAs, and 11% PUFAs and 85 mg cholesterol/1000 kcal), which met the National Cholesterol Education Program (NCEP) Step 2 guidelines; (3) a reduced-fat diet, in which two thirds of the fat was provided as beef tallow (beef tallow-enriched diet: 31% fat with 13% SFAs, 11% MUFAs, and 3% PUFAs and 109 mg cholesterol/1000 kcal); and two reduced-fat diets, one (4) enriched in corn oil and the other (5) enriched in beef tallow, to which moderate amounts of cholesterol in the form of egg yolk were incorporated (197 or 226 mg cholesterol/1000 kcal final cholesterol content in corn oil- or beef tallow-enriched diets, respectively). All diets were isocaloric and all food and drink were provided by the metabolic kitchen. Reducing the fat content of the diet resulted in decreased concentrations of LDL-C and high-density lipoprotein cholesterol (HDL-Q. Reductions in LDL-C concentrations were greatest when subjects consumed the corn oil-enriched diet (-17%) relative to the beef tallowenriched diet (‐8%). Similar reductions in HDL-C concentrations were observed regardless of the fat source (corn oilenriched diet, ‐9%; beef tallow‐enriched diet, ‐7%). LDL apolipoprotein (apo) B concentrations tended to mirror those of total cholesterol. In contrast to the changes observed in HDL-C concentrations, there was no significant effect of diet on apoA-I concentrations. The addition of modest amounts of cholesterol (equivalent to about 1.5 eggs per day) to the com oil-enriched diet resulted in significantly higher concentrations of total cholesterol (6%), LDL-C (8%), and HDL-C (7%). In contrast, addition of similar amounts of cholesterol to the beef tallowenriched diet resulted in significantly higher concentrations of total cholesterol (5%) and LDL-C (11%) but not HDL-C. In summary, these data suggest that even within the context of a reduced-fat diet, substitution of beef tallow, a commonly consumed fat that is relatively high in stearic acid, for com oil resulted in higher plasma cholesterol levels, possibly as a result of the concomitant addition of other, more hypercholesterolemic fatty acids.