Maintenance of blood glucose homeostasis in fasting man requires establishment of a fine
balance between glucose production and utilization. Early in starvation, a decrease in serum
insulin provides the alterations in substrate concentration and enzymatic activity conducive
to augmented gluconeogenesis. As fasting progresses, glucose utilization is reduced as the
brain consumes ketone bodies. A concomitant reduction in total gluconeogenesis is brought
about by a reduction in plasma amino acid levels, particularly alanine.