Glycogen is a stored form of glucose (a type of sugar) that serves as a key energy reserve in the body. It is a polysaccharide made up of long chains of glucose molecules, linked together in a branched structure, which makes it highly efficient for quick energy release.
Where Glycogen is Stored
- Liver:
- Acts as a glucose reservoir for the entire body.
- Releases glucose into the bloodstream to maintain blood sugar levels, especially during fasting or between meals.
- Storage: ~100–120 grams (equivalent to ~400–480 calories).
- Muscles:
- Provides energy directly to muscle cells during exercise or physical activity.
- Glycogen in muscles cannot be released into the bloodstream; it is used locally by the muscle cells.
- Storage: ~300–400 grams (depending on muscle mass and training status).
- Small Amounts in Other Tissues:
- Trace amounts are found in the brain, kidneys, and red blood cells.
Function of Glycogen
- Energy Storage:
- Maintaining Blood Sugar:
- Liver glycogen helps regulate blood glucose levels, ensuring the brain and other organs have a steady energy supply.
- Fuel for Exercise:
- Muscle glycogen is the primary fuel source for moderate to high-intensity exercise.
How Glycogen Works
- Synthesis (Glycogenesis):
- When you consume carbohydrates, excess glucose is converted into glycogen and stored in the liver and muscles.
- Breakdown (Glycogenolysis):
- During fasting, physical activity, or low blood sugar, glycogen is broken down into glucose for energy.
- Depletion:
- Prolonged exercise or fasting can deplete glycogen stores, leading to fatigue or the need for refueling.
Factors Affecting Glycogen Storage
- Carbohydrate Intake:
- Exercise:
- Training Status:
- Endurance-trained individuals store more glycogen than sedentary individuals.
Signs of Glycogen Depletion
- Fatigue during prolonged exercise (commonly known as “hitting the wall”).
- Reduced performance in high-intensity or endurance activities.
- Low energy and lethargy during prolonged fasting or low-carb diets.
Replenishing Glycogen
- Carbohydrate Consumption:
- Carb-Protein Combination:
- Combining carbohydrates with protein (e.g., 3:1 carb-to-protein ratio) can speed up glycogen resynthesis.
- Glycogen Supercompensation (Carb Loading):
- Used by endurance athletes to maximize glycogen stores before long-duration events.
Why Glycogen is Important
- Essential for maintaining energy levels during exercise and daily activities.
- Plays a critical role in stabilizing blood sugar levels.
- Enhances athletic performance and recovery.