What Does the Body Use Liver Glycogen for?

December 30, 2025 •

4 min read

According to the Cleveland Clinic, the body primarily stores glucose as glycogen in the liver and muscles for later use. The main function of this liver glycogen is to regulate the body's blood glucose levels, ensuring a steady supply of energy for vital organs. This function is critical during periods of fasting or increased energy demand.

Quick Summary

The liver stores excess glucose as glycogen to maintain stable blood sugar levels. When blood glucose drops, hormones trigger the liver to break down glycogen and release glucose into the bloodstream, providing crucial energy for the brain and other tissues. This process is essential for survival during fasting and high-energy demands.

Key Points

Blood Glucose Buffer: Liver glycogen's main purpose is to maintain stable blood glucose levels for the entire body, especially for the brain.
Fasting Survival: During fasting, the liver breaks down its glycogen stores and releases glucose to prevent hypoglycemia and supply energy to vital organs.
Hormonal Regulation: Glucagon triggers the release of liver glycogen in response to low blood sugar, while insulin promotes its storage after meals.
Distinction from Muscle Glycogen: Unlike liver glycogen, muscle glycogen is used exclusively by the muscle cells and cannot be released into the bloodstream.
Exercise Support: Liver glycogen provides a sustained release of glucose during prolonged exercise, ensuring both the brain and working muscles have fuel.
Impact of Dysregulation: Inherited conditions known as Glycogen Storage Diseases (GSDs) can impair the liver's ability to properly store or release glycogen.

The Central Role of Liver Glycogen

Liver glycogen is a highly branched polysaccharide of glucose, acting as the body's primary glucose reserve. Unlike muscle glycogen, which serves as a fuel source exclusively for the muscles, liver glycogen is used to maintain blood glucose homeostasis for the entire body. This function is particularly vital for the brain, which relies almost exclusively on glucose for energy. The regulation of liver glycogen is a finely tuned process mediated by hormones like insulin and glucagon, which respond to fluctuations in blood sugar levels.

Maintaining Blood Glucose Homeostasis

The most important function of liver glycogen is to act as a buffer for blood glucose levels. After a meal, when carbohydrate intake causes blood glucose to rise, the pancreas releases insulin. Insulin signals the liver to take up excess glucose from the bloodstream and convert it into glycogen for storage through a process called glycogenesis. This prevents blood sugar from rising too high. Conversely, during periods of fasting or between meals, blood glucose levels begin to drop. This triggers the pancreas to release glucagon. Glucagon signals the liver to break down its stored glycogen back into glucose through glycogenolysis and release it into the bloodstream. This rapid conversion and release mechanism ensures that critical organs, especially the brain, have a continuous energy supply. After about 24 hours of fasting, liver glycogen stores are significantly depleted, and the body must turn to other energy sources, such as converting fat and protein into glucose via gluconeogenesis.

Supporting Brain Function

The brain is a glucose-dependent organ, consuming a large portion of the body's total energy, even during rest. Its constant need for a stable supply of glucose is why liver glycogen's role in blood sugar regulation is so critical. Without a consistent release of glucose from the liver, hypoglycemia (low blood sugar) would occur, leading to impaired cognitive function, seizures, or even loss of consciousness. During an overnight fast, the liver diligently breaks down its glycogen stores to provide the brain with the fuel it needs to function properly.

Fuelling Physical Activity

While muscle glycogen is the primary fuel for muscle contraction during exercise, liver glycogen also plays a crucial supporting role, particularly during prolonged activity. As working muscles deplete their own glycogen stores, they draw more glucose from the bloodstream. To maintain stable blood glucose levels and prevent fatigue, the liver increases its rate of glycogenolysis, releasing glucose to replenish the circulating supply. This coordinated effort allows for sustained physical performance, especially during endurance exercise, by ensuring that both muscles and the central nervous system have adequate energy.

Impact of Liver Glycogen Disorders

Dysregulation of liver glycogen metabolism can lead to serious health conditions. Glycogen Storage Diseases (GSDs), for example, are genetic disorders caused by deficiencies in the enzymes that control glycogen synthesis or breakdown. This can result in abnormal glycogen accumulation in the liver, causing hepatomegaly (enlarged liver) and hypoglycemia. In conditions like glycogenic hepatopathy, often seen in uncontrolled diabetes, reversible glycogen buildup can also occur in the liver. These examples underscore the intricate and essential nature of liver glycogen's function in maintaining overall health.

List of Factors Influencing Liver Glycogen Use

Hormonal Signals: The hormones insulin and glucagon are the primary regulators, with insulin promoting glycogen storage and glucagon promoting its breakdown.
Fasting vs. Fed State: The body relies on liver glycogen primarily during fasting or between meals to maintain blood sugar. After eating, the liver shifts to storing glycogen.
Exercise Intensity and Duration: While muscle glycogen powers intense activity, liver glycogen becomes a more significant source of blood glucose during prolonged exercise to fuel muscles and the brain.
Dietary Carbohydrate Intake: The amount of carbohydrates consumed directly impacts how much glycogen the liver can store. A low-carb diet will result in lower glycogen stores.
Stress Hormones: Adrenaline (epinephrine) also stimulates liver glycogenolysis in response to stress or a 'fight-or-flight' situation, providing a rapid energy boost.

Liver Glycogen vs. Muscle Glycogen: A Comparison


Feature	Liver Glycogen	Muscle Glycogen
Primary Role	Regulates blood glucose for the entire body.	Provides a local energy source for muscle contraction.
Glucose Release	Can be released into the bloodstream to raise blood sugar levels.	Cannot be released into the bloodstream, as muscle cells lack the enzyme glucose-6-phosphatase.
Total Store	Approximately 100 grams, but with a higher concentration per cell.	Approximately 500 grams in skeletal muscles overall.
Hormonal Control	Responsive to both glucagon and adrenaline.	Primarily responsive to adrenaline and exercise itself, not glucagon.
Depletion Time	Depletes relatively quickly during fasting (~24 hours).	Depletes during intense or prolonged exercise.

Conclusion: A Vital Energy Regulator

The liver's glycogen stores are essential for maintaining the body's energy balance and ensuring the uninterrupted function of the brain and other vital organs. By acting as a central glucose reservoir, the liver can release glucose into the bloodstream on demand, especially during periods of fasting or exercise. This dynamic process, controlled by hormones like insulin and glucagon, ensures that blood sugar levels remain stable, preventing dangerous drops in blood glucose. Understanding the specific roles of liver glycogen, particularly in contrast to muscle glycogen, highlights the liver's crucial role as a metabolic powerhouse in the human body. National Center for Biotechnology Information provides further resources on the biochemical pathways of glycogenolysis. Its proper function is integral to both everyday energy needs and survival during periods of nutrient deprivation.

Frequently Asked Questions

The primary difference is their function and mobility. Liver glycogen is used to regulate blood glucose for the entire body and can be released into the bloodstream, while muscle glycogen is stored and used locally by the muscles for their own energy needs and cannot be released into the blood.

During fasting, as blood glucose levels drop, the pancreas releases the hormone glucagon. This signals the liver to break down its stored glycogen (glycogenolysis) and release glucose into the bloodstream to maintain stable blood sugar and provide energy for the brain and other organs.

Liver glycogen can be significantly depleted during prolonged fasting. After approximately 24 hours without carbohydrate intake, the liver's glycogen stores are largely exhausted, and the body shifts to other energy sources, like fats and proteins.

Yes, liver glycogen plays an important supporting role during prolonged exercise. As muscle glycogen is depleted, the liver releases glucose into the bloodstream to ensure working muscles and the brain have a continuous supply of fuel.

Glycogenesis is the process by which the liver converts excess glucose into glycogen for storage. Glycogenolysis is the reverse process, where the liver breaks down stored glycogen back into glucose for release into the blood.

Hormones are key regulators. Insulin, released after eating, promotes glycogen storage. Glucagon, released during fasting or low blood sugar, triggers glycogen breakdown.

Impaired liver glycogen metabolism can lead to various health issues, including glycogen storage diseases (GSDs). These genetic disorders result from enzyme deficiencies that cause abnormal glycogen storage, leading to complications like hypoglycemia and an enlarged liver.