Figure 5.

The disposition index (DI) is the product of insulin sensitivity (Si) and the insulin response to glucose (IRG). In subjects with normal fasting plasma glucose concentration and normal glucose tolerance, Si is related to IRG in a hyperbolic fashion. In obese subjects with normal glucose tolerance, an increase in the β-cell response to a glucose challenge compensates for decreased insulin sensitivity and maintains normal glucose homeostasis (a → b; no change in DI). However, an inadequate β-cell response to a decrease in insulin sensitivity results in impaired glucose homeostasis and eventually type 2 diabetes (a → c; reduction in DI).