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.
Felig P, Marliss E, Owen OE, Cahill GF. Blood Glucose and Gluconeogenesis in Fasting Man. Arch Intern Med. 1969;123(3):293-298. doi:10.1001/archinte.1969.00300130075011