Glycogen and glucagon sound almost identical, which is why some people mix them up. They are completely different things. One is a stored form of carbohydrate that fuels your training. The other is a hormone that raises blood sugar when it drops too low. Understanding the difference helps you make sense of energy levels, cravings, weight loss, endurance training and even how diabetes management works.
This blog explains both in simple terms you can actually use.
What Is Glycogen?
Glycogen is the storage form of carbohydrate. When you eat carbs, your body breaks them down into glucose. Some of that glucose is used immediately for energy. The rest is stored as glycogen in the muscles and liver.
You can think of glycogen as your internal fuel tank. When you exercise or go for long periods without eating, your body converts glycogen back into glucose and uses it to keep everything running.
Glycogen powers:
- moderate and high intensity exercise
- all types of running
- cycling, especially hills and efforts
- strength training
- daily movement and concentration
When glycogen gets low, you may feel tired, heavy, sluggish or hungry. This is why training sessions feel harder when you have not eaten enough, and why proper fuelling makes such a noticeable difference.
What Is Glucagon?
Glucagon is a hormone produced by the pancreas. Its job is to raise blood sugar when it drops too low. It does this by telling the liver to release stored glucose into the bloodstream.
If insulin lowers blood sugar, glucagon raises it. They work together to keep things stable.
You rely on glucagon when:
- you have gone a long time without eating
- your blood sugar dips
- you are doing long sessions and glycogen is running low
- you start to feel shaky or lightheaded
Glucagon is a safety net. It stops blood sugar dropping to unsafe levels.
How Glycogen and Glucagon Affect Weight Loss
Glycogen plays a much bigger role in weight loss than most people realise. When glycogen is low, you often get stronger cravings for carbohydrates because your body is trying to refill its fuel tank. You might also notice that exercise and training sessions feel harder, which lowers the number of calories you burn and makes movement feel less effortless.
Low glycogen usually makes people move less without realising. You may sit more, stand less or skip steps because you feel tired, and this can slow progress even when calories look similar.
The scale also reacts to glycogen changes. Glycogen binds water, so when you reduce carbs, the scale drops quickly. This is water loss from your body and muscles, not body fat. When you eat more carbs, glycogen stores refill and the scale goes up again. This is normal.
Glucagon does not directly affect fat loss. It simply keeps your blood sugar stable. When calories are low, glucagon rises slightly so the liver can maintain a safe level of glucose. It does not make you store fat or burn fat. It simply prevents dips that would make you feel unwell.
How Glycogen and Glucagon Matter for Runners and Cyclists
For runners and cyclists, glycogen is everything. It is the primary fuel for pace, power and anything that requires effort above a gentle jog. When glycogen gets low, you slow down, lose power and struggle with hills or surges.
If you start a long run or ride under fuelled, you deplete glycogen quickly and hit the wall. This is not dehydration or lack of fitness. It is a simple lack of fuel.
Glucagon helps by releasing glucose from the liver, which can delay a crash, but it cannot compensate for empty glycogen stores. This is why long sessions almost always require some kind of carbohydrate intake during training. Gels, chews and sports drinks work because they supply glucose faster than the body can produce it.
Without enough glycogen, training quality drops. Poor training quality reduces fitness gains, increases injury risk and makes a training session harder to stick to.
How Glycogen and Glucagon Matter in Type 1 Diabetes
Type 1 diabetes affects both insulin and glucagon. People with type 1 do not produce insulin, and many also have a reduced glucagon response. This makes low blood sugar during exercise more dangerous because the liver does not always release glucose when needed.
During training:
- muscles are using glucose
- injected insulin still lowers blood sugar
- glucagon may not step in reliably
This increases the risk of hypos. That is why people with type 1 diabetes often need to take in carbohydrate before, during or after exercise depending on their levels. It is also why careful planning is important.
Glycogen becomes even more important for safety. If glycogen stores are low, there is less backup fuel for the liver to release. People with type 1 often need to monitor their levels more closely during long runs, rides or hard sessions.
How Glycogen and Glucagon Matter in Type 2 Diabetes
Type 2 diabetes is very different from type 1. People with type 2 still produce insulin, but their body does not respond to it properly. Glucagon release can also become inappropriate. This means glucagon may tell the liver to release glucose even when blood sugar is already high, especially overnight. This is one reason morning levels can be elevated.
Glycogen matters in type 2 diabetes because regular movement improves the muscles’ ability to store and use glycogen. Better glycogen handling improves insulin sensitivity. This is one of the biggest reasons exercise is helpful for managing type 2 diabetes.
Low glycogen increases cravings, which can lead to overeating and less predictable blood sugar patterns. When glycogen levels are steady and managed well, people tend to feel more in control of their appetite and energy.
Bringing It All Together
Glycogen and glucagon may sound similar, but they have completely different roles:
- Glycogen provides fuel for exercise and everyday energy
- Glucagon prevents blood sugar dropping too low
For weight loss, managing glycogen helps with cravings, energy levels and training quality. For runners and cyclists, glycogen is the difference between strong sessions and struggling through them. In type 1 diabetes, a reduced glucagon response means careful fuelling is essential. In type 2 diabetes, exercise helps the muscles use glycogen more effectively and improves insulin sensitivity.
Understanding these two concepts makes nutrition and training far easier to manage, even without getting technical.
If you want help building a training and nutrition plan that fits your lifestyle and supports your goals, I can guide you through it step by step:
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Disclaimer: Nothing in this blog is intended to be medical advice. If you are living with type 1 or type 2 diabetes, or if you have concerns about any medical condition, always speak to your GP or another appropriate healthcare professional. If you think you may have diabetes or need help managing symptoms, please seek medical guidance before making changes to your diet, training or medication.
