Effect of caloric restriction on the glucose tolerance and plasma insulin of the sand rat

Three groups of sand rats have been studied to determine the effects of restricted versus unrestricted caloric intake on the plasma insulin levels and glucose tolerance. One group of animals was fed throughout the experiment on an allvegetable diet of about 30 calories per day. They developed and, for the most part, maintained a low plasma insulin level and normal glucose tolerance. A second group of sand rats was fed a synthetic diet in restricted amounts so that the total caloric value averaged 30 per day. These animals lost weight, had a low plasma insulin level and a normal glucose tolerance. When these same animals were fed the synthetic diet ad libitum, they consumed about 49 calories per day, they gained weight, their plasma insulin became markedly elevated and their glucose tolerance decreased. A third group of sand rats was fed a synthetic diet in a similar manner except that the order of restricted-ad libitum feeding was reversed. The resulting alterations in plasma insulin and glucose tolerance in general followed the same relation to caloric intake as seen in the previous group.