Updated 23rd April 2024

Glycogen, glucose, and glucagon: Their roles in your blood, sugar, and energy

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Glucose is the sugar in your blood. It’s your body’s main source of fuel. Glycogen is a form of glucose that’s stored in your cells for later.

Glucagon is a hormone that triggers the release of glycogen back into your bloodstream when you need it.

In this article, we’ll explore how these substances work together to balance your blood sugar and energy levels.

Differences in glucose, glycogen, and glucagon

Let’s look at the differences and interactions between these substances in more detail.


Glucose is the main type of sugar in your blood. When people talk about their blood sugar levels, they mean the amount of glucose in their blood.

Glucose is your body’s primary source of fuel: It powers your muscles, your brain, and your other organs.

It’s a simple sugar consisting of a single molecule. This means it’s a “monosaccharide.”

You mainly get glucose from digesting the carbohydrates in your food. 


Glycogen is a form of glucose. Your body stores it until it needs the energy. 

Glycogen molecules are made up of thousands of glucose molecules.

So, while glucose is a monosaccharide, glycogen is a “polysaccharide.”

You mostly store glycogen in your liver and muscles. We’ll look at glycogen’s storage and use in more detail later on.


Glucagon is a hormone. It tells your body to break down the glycogen stored in your liver. This means turning it back into glucose. 

The glucose then enters your bloodstream so your cells can use it as fuel.

Your pancreas releases glucagon when your blood sugar levels drop too low, and your body needs more energy.

Glucagon does the opposite of insulin. Insulin is a hormone that triggers your cells to absorb glucose from your blood when your blood glucose levels get too high.

So, glucagon helps release glucose into your blood. Insulin helps remove it.

Editor’s summary

  • Glucose is a simple sugar and your body’s main source of energy.

  • Glycogen is a form of glucose stored mainly in your liver and muscles. Your body can use it for energy when it’s needed.

  • Glucagon is a hormone. It gets your liver to convert glycogen back into glucose and release it into your bloodstream.

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How does glucose become glycogen?

Glucose is turned into glycogen through a process called glycogenesis.

A series of chemical reactions change the structure of glucose molecules. Each reaction uses different proteins called enzymes to make these changes.

The final reaction brings these altered glucose molecules together to form glycogen. 

A single glycogen molecule in your muscles can contain 5,000 glucose molecules. A glycogen molecule in your liver can contain over 50,000.

Where is glycogen stored?

Glycogen is mostly stored in your liver and muscles.

You can also find small amounts in other places, including your kidneys, heart, and brain, as well as in fat and blood cells.

What does glycogen do in the body?

Most glycogen is in your liver and muscles. It can be released and used as energy when you need it. 

Glycogen is essential for maintaining healthy levels of blood glucose and ensuring that your organs and muscles can function properly.

The glycogen in your liver is used for energy all around your body, including your brain.

The glycogen in your muscles isn’t released into your bloodstream. It’s only used by the muscles themselves. 

When does your body use glycogen?

When your blood glucose drops below a certain level, glucagon is released.

This triggers the glycogen in your liver to be broken down into glucose, which enters your bloodstream.

This glucose provides fuel for most cells in your body. When you start to do more exercise, your muscles use the glycogen they’ve stored.

In your muscles, glycogen is stored alongside large amounts of water. When the glycogen is converted back to glucose, this water is also released.

That’s why people often lose weight when they start a low-carb diet. Much of this weight loss is water being released from muscles as glycogen makes up for the lack of carbs. 

When the glycogen and water in your muscles builds back up, you’ll likely stop losing weight and may even regain some of what you lost.

Editor’s summary

The glycogen in your liver can provide energy for your organs, including your brain. The glycogen in your muscles can help fuel movement.

When your blood glucose levels fall, the hormone glucagon triggers the glycogen in your liver to turn back to glucose. This glucose enters your bloodstream, where it can provide energy to the cells that need it.

What does glucose do in the body?

Glucose is your main fuel source. It provides energy to almost all of your cells. 

It’s responsible for the proper functioning of your muscles, your brain, and your other organs.

We get glucose from what we eat. What’s fascinating is that your blood glucose levels respond differently from other people’s.

A food that leads to a quick rise in blood sugar in one person may cause a much slower rise in someone else.

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Our at-home test measures your gut health — and how your blood sugar and fat levels respond to food. With this information, our personalized nutrition program can help you eat the best foods for you.

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Do any tests measure glycogen levels?

Elite athletes sometimes undergo glycogen testing, but most of us won’t.

Your glycogen levels change throughout the day, depending on what you’ve eaten and how much exercise you’ve done. 

If a doctor wants to understand your glycogen levels, they likely think you could have a genetic disorder called glycogen storage disease (GSD). 

Some tests for GSD do show glycogen levels, but most look for other signs of the condition. 

Types of test for diagnosing GSD include: 

  • Blood tests: Unusual levels of glucose, fats, and other substances in your blood can indicate GSD. 

  • Genetic tests: Analyzing your DNA for specific mutations will show if you have the condition.

  • Biopsies: A sample of liver or muscle tissue can show signs of GSD, including low glycogen levels.

What is glycogen storage disease?

GSD is an umbrella term for certain very rare inherited conditions that keep your body from processing glycogen properly.

Forms of GSD can stem from a lack of different enzymes. This may mean that your body can’t store glycogen or can’t use it for energy.

Different types of GSD cause different symptoms, but they can include:

  • low blood sugar

  • an enlarged liver

  • muscle cramps

  • muscle weakness

  • pain, sickness, or extreme tiredness after exercise

  • heart problems

Frequently asked questions

Here we’ll take a brief look at some other questions about glycogen and glucose.

Is glycogen a carbohydrate?

Though glycogen isn't in our food, it’s technically a carbohydrate. 

As we’ve seen, glucose is a single-molecule sugar. Glycogen is made up of thousands of glucose molecules.

Both of these substances are sugars, and all sugars are carbohydrates.

What is glycogenolysis?

Glycogenolysis is the chemical process that converts glycogen stored in your muscles and organs back into glucose. 

In your liver, glycogenolysis releases glucose into your bloodstream to be used around your body. In your muscles, glycogenolysis releases glucose that your muscles use directly. 

The reverse process — glucose transforming into glycogen for storage — is called glycogenesis. 

What is gluconeogenesis?

Gluconeogenesis is another chemical process: Your body turns fats and protein into glucose to use as fuel.

This is happening all the time to some degree. But it happens more when you’re not getting  enough glucose from your food or your stores of glycogen.

You may be following a low-carb diet or fasting.

What happens when you run out of glycogen?

If you exercise for long enough — generally around 90 mins or more — your glycogen stores start to run low. 

This leads to tired muscles and fatigue: You’ve run out of energy. 

But once you eat, your body quickly starts to rebuild its stores of glycogen.

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Glucose is the sugar in your blood. It’s your body’s main fuel source, and it provides energy to your brain, your other organs, and your muscles.

You usually get glucose from carbs in your food. If your diet is low in carbs, you’ll start to convert fat and protein into glucose instead. This process is called gluconeogenesis.

Glycogen is a form of glucose that’s stored in your liver, muscles, and elsewhere in your body. It’s converted back into glucose when needed.

Glucagon is a hormone that triggers your liver to convert glycogen into glucose and release it into your bloodstream. It’s the counterpart to insulin, which prompts your cells to store glycogen.

Together, these different substances help balance your blood sugar and energy levels.


Biochemistry, glycogenolysis. (2022). https://www.ncbi.nlm.nih.gov/books/NBK554417/ 

Carbohydrates. (2022). https://medlineplus.gov/carbohydrates.html 

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Carbohydrates. (n.d.). https://www.hsph.harvard.edu/nutritionsource/carbohydrates/

Fundamentals of glycogen metabolism for coaches and athletes. Nutrition Reviews. (2018). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6019055/ 

Glucagon physiology. (2019). https://www.ncbi.nlm.nih.gov/books/NBK279127/

Glycogenesis. (n.d.). https://bio.libretexts.org/Bookshelves/Biochemistry/Fundamentals_of_Biochemistry_(Jakubowski_and_Flatt)/02%3A_Unit_II-_Bioenergetics_and_Metabolism/15%3A_Glucose_Glycogen_and_Their_Metabolic_Regulation/15.02%3A_Glycogenesis 

Glycogen storage disease. (2023). https://www.ncbi.nlm.nih.gov/books/NBK459277/

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Postexercise muscle glycogen resynthesis in humans. Journal of Applied Physiology. (2017). https://journals.physiology.org/doi/full/10.1152/japplphysiol.00860.2016 

State-of-the-art methods for skeletal muscle glycogen analysis in athletes: The need for novel non-invasive techniques. Biosensors. (2017). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5371784/

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