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. This glycation may turn out to be a useful measure of health or functional age. A lthough diet books and magazines have begun to recommend calorie restriction as a key to a longer and healthier human life, Roth and other primate researchers do not. Even given the dramatic health benefits, it's hard to imagine many people adopting a daily diet that would be the caloric and nutritional equivalent of a couple of cans of Slimfast, when more palatable health-promoting advice, such as eating five fruits or vegetables a day, has had relatively few takers in the United States. Calorie restriction started at an early age seems to delay the onset of sexual maturity by about a year, although once the monkeys mature, their hormone cycles seem to be normal.