At the start of the Wisconsin study, insulin concentrations after fasting indicated that four of the monkeys had a genetic risk of diabetes. Two of them were put on the restricted diet. Four years later, four monkeys in the control group, but none in the restricted group, had signs of an impaired response to blood sugar. The impaired group included the two at-risk animals. In animals, including people, the body's response to insulin falls off with age.
Cells take up less glucose, leaving too much in the bloodstream.
The calorie-restricted animals have so far maintained tight regulation of glucose and insulin. With less glucose circulating in the system, there seems to be less of another problem. In glycation, glucose molecules stick to proteins and other essential molecules, gumming up a cell's smooth functioning and possibly contributing to aging. Cataracts are one result of the process. Restricted monkeys show less glycation of hemoglobin and collagen.