Abstract: There is little argument concerning blood cholesterol as a risk factor for coronary heart disease, but considerable controversy regarding the influence of diet on blood cholesterol. All dietary components can affect cholesterolemia. Fats of animal origin are more saturated than corn or safflower oils, but the saturated vegetable fats (coconut and palm oils) are the most cholesterolemic. Cocoa butter is a highly saturated fat but its high content of stearic acid renders it much less cholesterolemic than would be expected. Animal protein, fed as the only source of protein, is more cholesterolemic than vegetable protein, but an equal mixture of the two is not cholesterolemic. The type of fat or fiber in the diet also influences its cholesterolemic effect. These data point up the importance of considering nutrient interactions. In the area of diet and cancer, rats fed saturated fat exhibit fewer chemically-induced tumors than do those fed unsaturated fat. Caloric restriction will inhibit carcinogenesis in rodents regardless of the type or amount of fat present in the diet. The observation that excessive caloric intake increases mortality was made by Lucretius in 50 B.C. It may be as true 2000 years later. Key words: Animal protein, cholesterol, experimental carcinogenesis, heart disease, lipoproteins