Fasting Phase
When you’re sleeping or go long periods without eating, your body needs to have a supply of energy to keep your organs functioning. Once you use up all of your available glucose during the digestive phase of metabolism (your body stores only about 300 calories in the short-term glycogen reservoir), it taps a long-term reservoir: fatty tissue in the form of triglycerides (molecules that include a carbohydrate-containing glycerol). This keeps you going until you break the fast with breakfast.