Digestive Phase
Your hypothalamus orchestrates this phase of metabolism by receiving signals from throughout your body about whether you’re hungry or not, so that your body can use energy to power itself. Here’s how: Your body has a short-term reservoir for energy in the form of glycogen, a carbohydrate primarily stored in your liver and muscles. After eating, when you have glucose (sugar) and insulin (the hormone produced in the pancreas to transport glucose), your body uses all of the glucose it needs for immediate fuel but takes the rest and stores it as glycogen. If your blood glucose level falls, your pancreas stops releasing insulin—and then releases another G substance, glucagon, which converts the stored energy (glycogen) to sugar (glucose). So the effect is that when your intestinal gas tank empties of sugar (in other words, when our ancestors were fasting between bison hunts), your body is still able to supply crucial energy to your central nervous system by converting glycogen to glucose.