The effects of consumption of diets high in sucrose and cornstarch on glucose and lipid metabolism in Zucker fatty and lean rats and Sprague-Dawley rats were investigated in the present study. Rats of each strain or genotype, 8 to 10 months of age, were fed diets containing 56% cornstarch or 57% sucrose for 4 weeks, when an intraperitoneal glucose tolerance test was administered. After 2 additional weeks of dietary treatment, the rats were sacrificed and plasma was collected. The plasma was assayed for triglyceride and cholesterol concentration. Plasma VLDL were isolated by ultracentrifugation and were assayed for triglyceride. Pooled VLDL samples from each group were separated by size using a 2% agarose column. Sprague-Dawley rats fed sucrose had higher final body weights than rats of the same strain fed cornstarch. For lean or obese Zucker rats, however, there was no difference in final body weights due to dietary treatment. No rats fed cornstarch gained weight throughout the study. Lean Zucker rats and Sprague-Dawley rats fed sucrose gained weight when fed the sucrose diet, although Zucker fatty rats did not. Zucker lean and Sprague-Dawley rats fed sucrose consumed more food throughout the study than animals of the same strain or genotype fed cornstarch. Zucker fatty rats, however, consumed the same amount of food regardless of dietary treatment. Fasting blood glucose concentrations were not affected by the dietary treatment within any strain or genotype investigated. However, Zucker fatty rats fed cornstarch did have significantly higher fasting blood glucose levels than Zucker lean or Sprague-Dawley rats fed cornstarch. This strain difference was not noted for groups fed the sucrose diet. Sucrose consumption resulted in an increased glucose tolerance curve peak with a similar decline of the curve for Zucker lean and Sprague-Dawley rats. This pattern was not observed for Zucker fatty rats fed sucrose. These rats had elevated blood glucose levels at 180 minutes after glucose injection, possibly indicating delayed glucose clearance in these rats; Zucker fatty rats generally had an elevated glucose tolerance curve compared to Zucker lean and Sprague-Dawley rats, regardless of dietary treatment. Plasma lipid concentrations of Zucker fatty rats responded differently to the dietary treatment than those of Zucker lean and Sprague-Dawley rats. Sucrose feeding caused increased plasma and VLDL triglyceride concentrations in Zucker lean and Sprague-Dawley rats, whereas no elevation of triglyceride levels occurred in Zucker fatty rats. Increased cholesterol levels due to sucrose feeding were observed only in Sprague-Dawley rats. There were no VLDL size differences observed for any strain or genotype and diet combination investigated. This may be due to the similarity of relative concentrations of VLDL triglyceride observed for all groups. This study demonstrated a difference in response of glucose tolerance and plasma and VLDL triglyceride concentrations of Zucker fatty rats fed sucrose compared to Zucker lean and Sprague-Dawley rats fed the same diet. / Ph. D.