Epidemiologic evidence indicated a relationship between refined sugar intake and increased serum cholesterol levels and atherosclerotic heart disease, which resulted in a series of human and animal experiments examining this relationship. Sucrose and fructose were found to be more atherogenic in rabbits and baboons when fed as part of a semipurified diet. However, serum lipid levels were not always elevated when more severe atherosclerosis was present. Human studies generally observed increases in serum triglycerides and, less consistently, serum cholesterol in response to substitution of sucrose for starch or glucose. These differences in lipid levels and experimental atherosclerosis are thought to arise from 1) increased endogenous triglyceride synthesis, present in serum as very low-density lipoproteins; 2) impaired clearance of these lipoproteins; 3) slowed turnover of cholesterol into bile acids; and 4) possible changes in aortic connective tissue metabolism.