Physical activity, the brain, and other vital organs require glucose consumption to keep going. The food digested is converted into glucose, present in abundance after consuming meals. When there is excess glucose, the body stores it as glycogen in the liver or converts it to fat, which causes weight gain and other health problems.n2. During the fasting state, roughly eight hours after eating, glucose levels are low, and the body gets the required glucose from the stored glycogen. Glycogen is broken down (a process known as glycogenolysis) and converted to glucose (known as gluconeogenesis). The body will use this glucose as fuel. n3. The body lacks stored glucose during intermittent fasting or prolonged fasting, so ketogenesis occurs. The breakdown of fat present in adipose tissue releases ketone bodies.