Figure 77-2 General scheme of fuel metabolism in normal, fasted humans, emphasizing the central position of the liver as a metabolic transformer. Two primary fuel sources are shown: muscle and adipose tissue. Three types of fuel consumers are shown: nerve, including brain; pure glycolyzers producing lactate (e.g., red blood cells, white blood cells); and the remainder of the body (e.g., heart, kidney, muscle), which can use fatty acids and ketones. The brain can also use ketone bodies after injury and in response to starvation. (Adapted from Cahill GJ Jr: Starvation in man. N Engl J Med 282:668, 1970.)