A metabolic adjustment that reserves the glucose produced by the liver for use by the nervous system.
In lipolysis, fat is broken down into glycerol and fatty acids. Glycerol is used to make glucose or in glycolysis. Fatty acids can be catabolized by many cells, especially aerobic muscle fibers. This is said to be 'glucose sparing' because it leaves glucose available for those cells, such as neurons, which rely on glucose exclusively. Glucagon and epinephrine also trigger lipolysis. Lipolysis begins when glycogen reserves fall to about 1/3 of maximum.