Metabolic System (IMAGE) Salk Institute Caption The metabolic system functions like a hybrid car. In the daytime we use glucose as high octane fuel, but at night we switch to the battery, which in this case is stored fat. Credit Image: Courtesy of Dr. Marc Montminy and Jamie Simon, Salk Institute for Biological Studies. Usage Restrictions News media reproduction to illustrate this story permitted with proper attribution as provided above. For one time use only. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.