Normally, decreased glucose production leads to increased mitochondrial fatty acid beta-oxidation and the production of ketones. Thus, ketones provide an indication of whether the hypoglycemia is a result of inadequate production or overutilization of glucose (which tends to be associated with low plasma ketone levels). Hypoketotic hypoglycemia developing within several minutes of feeding is typical of hyperinsulinism. A good starting point for evaluating hypoglycemia is to divide patients into ketotic or non-ketotic. Normal physiologic response to decreased glucose production is increased mitochondrial fatty acid beta-oxidation and the production of ketones. Ketones provide an indirect indication of whether hypoglycemia is the result of inadequate production or of over-utilization of glucose (insulin-induced over-utilization, associated with low urine or plasma ketones). The history of the relationship of the hypoglycemia to feeding is often helpful. Hypoketotic hypoglycemia developing within several minutes of feeding is typical of hyperinsulinism. Patients with defects in glycogen breakdown, gluconeogenesis, or fatty acid oxidation tend to tolerate short-term fasting much better.