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

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.

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

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.

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

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

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

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.

If you like diving deep into science, you might enjoy our newsletters. For the latest in ZOE’s research and insights into diet and nutrition, subscribe below.

Join the community

Be the first to know about ZOE’s breakthrough research, content from the world’s leading scientists, and more.

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. 

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 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.

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.

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.

At ZOE, we run the biggest nutrition science study in the world. We know that each person’s unique responses to food show that a one-size-fits-all approach to nutrition doesn’t work.

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.

Learn more about how it works and take our free quiz.

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. 

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.

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.

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.

Summary

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.

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.