What Is Glycogen? Role in Diet, Exercise and More

Every time you eat some type of food that contains carbohydrates, your body goes through a process of breaking down the food and converting its carbs to a type of sugar called glucose. When you have plenty of glucose available, more than your body can use at one time, it’s stored away for later use in the form of glycogen.

What is glycogen made of? It is synthesized from glucose when blood glucose (what we call “blood sugar”) levels are high.

It has the role of keeping blood glucose levels balanced by either storing excess glucose when levels rise or by releasing glucose when levels fall. This allows glycogen to function as an important “energy reservoir,” providing the body with energy as needed depending on things like stress, food intake and physical demands.

What is glycogen?

The definition of glycogen is “a tasteless polysaccharide (C₆H₁₀O₅)_x that is the principal form in which glucose is stored in animal tissues, especially muscle and liver tissue.”

In other words, it’s the substance that is deposited in bodily tissues as a store of carbohydrates. Research shows it functions as a type of energy storage, since it can be broken down when energy is required.

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What is the difference between glucose and glycogen? Glycogen is a branched polysaccharide (a carbohydrate that’s molecules consist of a number of sugar molecules bonded together) that is broken down into glucose.

Its structure consists of a branched polymer of glucose, made up of about eight to 12 glucose units. Glycogen synthase is the enzyme that links chains of glucose together.

Once broken down, glucose can then enter the glycolytic phosphate pathway or be released into the bloodstream.

What is the main function of glycogen? It serves as a readily available source of glucose and energy for tissues located throughout the body when blood glucose levels are low, such as due to fasting or exercising.

Just like with humans and animals, even microorganisms such as bacteria and fungi have the ability to store glycogen for energy to be used in times of limited nutrient availability.

Wondering about starch vs. glycogen and what the difference is? Starch is the main form of glucose storage in most plants.

Compared to glycogen, it has fewer branches and is less compact. Overall, starch does for plans what glycogen does for humans.

How it’s produced and stored

How does glycogen become glucose?

• Glucagon is a peptide hormone that’s released from the pancreas, which signals liver cells to break down glycogen.
• It is broken down via glycogenolysis into glucose-1-phosphate. It’s then converted to glucose and released into the bloodstream to provide the body with energy.
• Other hormones in the body that can also stimulate its breakdown include cortisol, epinephrine and norepinephrine (often called “stress hormones“).
• Studies show that glycogen breakdown and synthesis occur due to activities of glycogen phosphorylase, which is the enzyme that helps it break up into smaller glucose units.

Where is glycogen stored? In humans and animals it’s found mainly in muscle and liver cells.

In small amounts, it’s also stored in red blood cells, white blood cells, kidney cells, glial cells and the uterus in women.

Blood glucose levels rise after someone consumes carbohydrates, causing the release of the hormone insulin, which promotes the uptake of glucose into liver cells. When a lot of glucose is synthesized into glycogen and stored in liver cells, glycogen can account for up to 10 percent the weight of the liver.

Because we have even more muscle mass located throughout our bodies than liver mass, more of our stores are found in our muscle tissue. Glycogen accounts for about 1 percent to 2 percent of muscle tissue by weight.

While it can be broken down in the liver and then released in the bloodstream, this doesn’t happen with the glycogen in muscles. Research shows that muscles only provide glucose to muscle cells, helping power muscles but not other tissues in the body.

Benefits

The body uses glycogen to maintain homeostasis, or “stable equilibrium,” that is maintained by physiological processes.

The main function of glycogen metabolism is to store or release glucose to be used for energy, depending on our fluctuating energetic needs. It’s estimated that humans can store around 2,000 calories of glucose in the form glycogen at one time.

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There are several processes that the body uses to maintain homeostasis via glucose metabolism. These are:

• Glycogenesis or glycogen synthesis. This describes the conversion of glucose into glycogen. Glycogen synthase is a key enzyme involved in glycogenesis.
• Glycogenolysis or glycogen breakdown.

Benefits and roles of glycogen include:

• Serving as an important and quickly mobilized source of stored glucose.
• Providing a reserve of glucose for the body’s tissues.
• In the muscles, providing energy or “metabolic fuel” for glycolysis producing glucose 6-phosphate. Glucose is oxidized in muscle cells through anaerobic and aerobic processes to produce the adenosine triphosphate molecules, which are required for muscle contractions.
• Acting as a fuel sensor and regulator of signaling pathways involved in training adaptation.

In the human body, glycogen levels can vary dramatically depending on someone’s diet, exercise, stress levels and overall metabolic health.

It is released by the liver for a number of reasons in an attempt to bring the body back to balance. Some of the reasons it is released include:

• Upon waking up in the morning
• In response to low blood sugar as opposed to normal blood sugar
• Due to stress
• To help with digestive processes

Relationship to diet

Whenever you require a quick source of energy, which could be during or after exercise, your body has the option of breaking down glycogen into glucose to be ushered into the bloodstream. This is most likely to happen when the body doesn’t get enough glucose from food, such as if you’ve been fasting in order to get the benefits of fasting or haven’t eaten in more than several hours.

Depleting glycogen and shedding water weight will cause a drop in your body weight, although only temporarily.

After you exercise, many experts recommend that you “refuel” with a meal or snack that provides both carbs and protein, thereby helping replenish your glycogen stores and support muscle growth.

If you do about one hour of moderate-intensity exercise, then replenishing with 5–7 grams/kg of body weight of carbohydrates (plus protein) afterward is recommended to fully restore muscle glycogen within 24–36 hours.

What are some of the best glycogen foods to restore your reserves?

• The best options are unprocessed sources of carbohydrates, including fruits, starchy vegetables, whole grains, legumes/beans and dairy products. Consuming a diet that supplies enough carbohydrates and energy (calories) to match or exceed your daily needs results in a gradual buildup of muscle glycogen stores over several days.
• Amino acids, which form protein, also help the body use glycogen. For example, glycine is an amino acid that also helps break down and transport nutrients to be used by cells for energy. It’s been found to help inhibit the deterioration of protein tissue that forms muscle and boost performance and muscle recovery.
• Food sources like bone broth, collagen-rich foods and gelatin provide glycine and other amino acids, while other protein foods, such as meat, fish, eggs and dairy products, are also  beneficial.

Relationship to exercise

Muscle glycogen, as well as glucose in our blood and glycogen stored in the liver, helps provide fuel for our muscle tissues during exercise. This is one reason why exercise is strongly recommended for those with high blood sugar, including people with diabetes symptoms.

“Glycogen depletion” describes the state of this hormone being depleted from the muscles, such as due to vigorous exercise or fasting.

The longer and more intensely you exercise, the quicker your stores will be depleted. High-intensity activities, such as sprinting or cycling, can quickly lower stores in muscle cells, while endurance activities will do this at a slower pace.

Post-exercise, muscles need to then replenish their stores.

As a 2018 article published in Nutrition Reviews describes it, “The ability of athletes to train day after day depends in large part on adequate restoration of muscle glycogen stores, a process that requires the consumption of sufficient dietary carbohydrates and ample time.”

There are a couple of methods that athletes typically use to utilize glycogen in a way that supports their performance and recovery:

• They may load up on carbohydrates before a competition or difficult workout in order to increase their capacity to store glycogen and then use it when needed.
• In order to prevent poor performance due to fatigue caused by glycogen depletion, some endurance athletes also consume carbohydrates with high glycemic index scores during their workouts. This can help quickly and easily provide the muscles with more glucose to keep exercising.

You don’t necessarily need to eat lots of carbs to stay energized. A healthy, low glycemic diet is also effective.

Glycogen is the body’s “preferred” energy source, but it isn’t the only form of energy that can be stored. Another form is fatty acids.

This is why some athletes are able to perform well when following high-fat, low-carb diets, such as the ketogenic diet. In this case, the muscle can utilize fatty acids as an energy source once the person has become “fat adapted.”

Low-carb diets often promote weight loss, as can strenuous exercise, because they work by depleting glycogen stores, causing the body to burn fat instead for carbs for energy.

Risks and side effects

While they are not common diseases, some people deal with glycogen storage diseases, which develop when someone experiences “defective glycogen homeostasis” in the liver or muscles.

These diseases include Pompe disease, McArdle disease and Andersen disease. Some also consider diabetes to be a disease impacted by defective glycogen storage, since diabetics experience an impaired ability to clear glucose from their bloodstreams properly.

Why do these diseases develop? Impaired ability of the liver and muscles to store this hormone can happen for several reasons, such as due to:

• Genetic factors. Pompe disease is caused by mutations in the GAA gene, McArdle disease is caused by one in the PYGM gene and Andersen disease is caused by one mutation in the GBE1 gene.
• These diseases can happen at different stages of life and even be deadly if left untreated.
• Hepatomegaly (enlarged liver), hypoglycemia and cirrhosis (liver scarring) are other causes.

When someone experiences defective muscle glycogen storage, he or she can develop a number of symptoms and impairments. Examples include muscle pain and fatigue, stunted growth, liver enlargement, and cirrhosis.

Conclusion

• What is glycogen? It’s the stored form of glucose, which is the body’s main source of energy.
• It is made up of many connected glucose molecules.
• Its main function is to help the body maintain homeostasis by either storing or releasing glucose depending on our energy needs at any given time.
• Glycogen storage takes place mostly in the liver and muscle cells. The liver breaks down and releases it into the bloodstream when someone needs more energy than she’s taken in from food sources, especially carbohydrates.