Repeated weight fluctuation increases plasma insulin in the obese Wistar fatty diabetic rat

Weight fluctuation may contribute to the expression of hyperglycemia in genetically susceptible individuals. Alternating between diets with low and high fat content also may play a contributory role. To test these hypotheses, plasma glucose and insulin levels were measured in obese prediabetic Wistar-Fatty rats after two episodes of diet switching, with and without concomitant weight loss. Following two cycles of weight loss and regain, glucose levels did not differ between weight-cycled rats and static weight controls. However, insulin concentrations of weight-cycled rats were 74% higher than those of controls, suggesting an impairment of insulin resistance. Insulin and glucose levels of animals subjected to episodes of diet switching without accompanying weight loss and regain did not differ reliably from those of controls. A single cycle of weight loss followed by regain appeared to have no effect on either glucose tolerance or insulin resistance. Together, these results suggest that insulin resistance of Wistar-Fatty rats was worsened by repeated weight fluctuation. Further, the effect of repeated weight fluctuation on insulin concentrations is not due to diet switching. Repeated weight fluctuation did not lead to the expression of hyperglycemia under the present conditions. Additional studies are needed to determine what factors modify the effects of weight fluctuation on health, behavior, and metabolism.