Metabolic responses of Zucker fatty and lean rats fed carbohydrate diets ad libitum or in meals.

In order to study the metabolic effects of dietary sucrose on Zucker rats, young male fatty and lean rats were fed ad libitum or in meals (2 hours/day) for 4 weeks. Diets contained 54% carbohydrate as either sucrose, invert sugar or cooked cornstarch. A genotype effect (fatty versus lean) occurred with the activities of liver and adipose tissue lipogenic enzymes, relative total fat pad size and soluble adipose tissue protein levels in both ad libitum- and meal-fed rats, whereas a genotype effect occurred with food intake and relative liver size only in meal-fed rats and with body weight gain only in ad libitum-fed rats. The significance of diet effects varied with genotype and feeding pattern. The sucrose effect (sucrose versus starch) occurred with food efficiency and body weight gain, activities of liver lipogenic and gluconeogenic enzymes, relative liver size, relative total fat pad size and soluble adipose tissue protein levels in both ad libitum- and meal-fed rats, and with adipose lipogenic enzyme activities in meal-fed rats. The disaccharide effect (sucrose versus invert sugar) occurred with the activities of liver lipogenic enzymes, relative total fat pad size and soluble adipose tissue protein levels in ad libitum-fed rats and was greater in lean than in fatty rats. The data demonstrate that the Zucker fatty and lean rat can be used as sensitive models to study differential effects of dietary carbohydrate.