The substrate depleted earliest in the postoperative period is

The metabolic response to surgery (and other trauma) is a result of neuroendocrine stimulation that sharply accelerates protein breakdown, stimulates gluconeogenesis, and produces glucose intolerance. The glycogen stores are rapidly depleted because of a fall in insulin and a rise in glucagon levels in the plasma. The peripheral effects of the neuroendocrine secretion result in an increase in plasma levels of amino acids, free fatty acids, lactate, glucose, and glycerol. In the liver, the coisol and glucagon stimulate glycogenolysis, gluconeogenesis, and increased substrate uptake.