Understanding Glycogen: The Body’s Fuel Source

For individuals who are getting into exercise, fitness, and physical activity, can knowing how glycogen works help in workout recovery?

Glycogen

When the body needs energy, it draws on its glycogen stores. Low-carbohydrate, ketogenic diets and intense exercise deplete glycogen stores, causing the body to metabolize fat for energy. Glycogen is supplied through carbohydrates in an individual’s diet and is used to power the brain, physical activity, and other bodily functions. The molecules made from glucose are mainly stored in the liver and muscles. What is eaten, how often, and the activity level influence how the body stores and uses glycogen.  Restoring glycogen after physical activity or working out is a vital part of the recovery process.  The body can quickly mobilize glycogen from these storage sites when it needs fuel. Eating enough carbohydrates to reach health goals and activity levels is essential for success.

What Is It

• It is the body’s stored form of glucose or sugar.
• It is stored in the liver and muscles.
• It is the body’s primary and preferred energy source.
• It comes from carbohydrates in foods and drinks.
• It is made from several connected glucose molecules.

Production and Storage

Most carbohydrates eaten are converted to glucose, which becomes the body’s main energy source. However, when the body doesn’t need fueling, the glucose molecules become linked chains of eight to 12 glucose units, forming a glycogen molecule.

Process Triggers

• Eating a carbohydrate-containing meal will raise blood glucose levels in response.
• Increasing glucose signals the pancreas to produce insulin, a hormone that helps the body’s cells take up glucose from the bloodstream for energy or storage.
• Insulin activation causes the liver and muscle cells to produce an enzyme called glycogen synthase, which links glucose chains together.
• With enough glucose and insulin, glycogen molecules can be delivered to the liver, muscles, and fat cells for storage.

Since most glycogen is found in the muscles and liver, the amount stored in these cells varies depending on activity level, how much energy is burned at rest, and the foods eaten. The muscles primarily use glycogen stored in the muscles, while glycogen stored in the liver is distributed throughout the body, mainly to the brain and spinal cord.

Body Usage

The body converts glucose to glycogen through a process called glycogenesis. During this process, various enzymes help the body break down glycogen in glycogenolysis so the body can use it. The blood has a set amount of glucose ready to go at any given time. The insulin levels also drop when the level begins to decline, either from not eating or burning glucose during exercise. When this happens, an enzyme known as glycogen phosphorylase starts breaking the glycogen down to supply the body with glucose. Glucose from liver glycogen becomes the body’s primary energy. Short bursts of energy use glycogen, whether during sprints or heavy lifting. (Bob Murray, Christine Rosenbloom, 2018) A carbohydrate-rich pre-workout drink can provide energy to exercise longer and recover quicker. Individuals should eat a post-workout snack with a balanced amount of carbohydrates to replenish glycogen stores. The brain also uses glucose for energy, with 20 to 25% of glycogen going toward powering the brain. (Manu S. Goyal, Marcus E. Raichle, 2018) Mental sluggishness or brain fog can develop when not enough carbohydrates are consumed. When glycogen stores are depleted through exercise or insufficient carbs, the body can feel fatigued and sluggish and perhaps experience mood and sleep disturbances. (Hugh S. Winwood-Smith, Craig E. Franklin 2, Craig R. White, 2017)

Diet

What foods are eaten and how much physical activity an individual does also influence glycogen production. The effects can be acute if one follows a low-carb diet, where carbohydrates, the primary source of glucose synthesis, are suddenly restricted.

Fatigue and Brain Fog

• When first starting a low-carb diet, the body’s glycogen stores can be severely depleted and individuals may experience symptoms like fatigue and brain fog. (Kristen E. D’Anci et al., 2009)
• The symptoms begin to subside once the body adjusts and renews its glycogen stores.

Water Weight

• Any amount of weight loss can have the same effect on glycogen stores.
• Initially, individuals may experience a rapid drop in weight.
• Over time, weight may plateau and possibly increase.

The phenomenon is partly due to glycogen composition, which is also water. Rapid glycogen depletion at the onset of the diet triggers the loss of water weight. Over time, glycogen stores are renewed, and the water weight returns. When this happens, weight loss can stall or plateau. Fat loss can continue despite the short-term plateau effect.

Exercise

If undertaking a strenuous exercise routine, there are strategies to help avoid decreased performance that may be helpful:

Carbo-loading

• Some athletes consume excessive amounts of carbohydrates before working out or competing.
• Extra carbohydrates provide plenty of fuel.
• The method has fallen out of favor as it can lead to excess water weight and digestive issues.

Glucose Gels

• Energy gels containing glycogen can be consumed before or as needed during an event to increase blood glucose levels.
• For example, energy chews are effective supplements for runners to help increase performance during extended runs.

Low-Carb Ketogenic Diet

• Eating a diet high in fat and low in carbohydrates can put the body in a keto-adaptative state.
• In this state, the body begins to access stored fat for energy and relies less on glucose for fuel.

At Injury Medical Chiropractic and Functional Medicine Clinic, our providers use an integrated approach to create personalized care plans for each individual, often including Functional Medicine, Acupuncture, Electro-Acupuncture, and Sports Medicine principles. Our goal is to restore health and function to the body.

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Sports Nutrition and Sports Dietician

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References

Murray, B., & Rosenbloom, C. (2018). Fundamentals of glycogen metabolism for coaches and athletes. Nutrition reviews, 76(4), 243–259. doi.org/10.1093/nutrit/nuy001

Goyal, M. S., & Raichle, M. E. (2018). Glucose Requirements of the Developing Human Brain. Journal of pediatric gastroenterology and nutrition, 66 Suppl 3(Suppl 3), S46–S49. doi.org/10.1097/MPG.0000000000001875

Winwood-Smith, H. S., Franklin, C. E., & White, C. R. (2017). Low-carbohydrate diet induces metabolic depression: a possible mechanism to conserve glycogen. American journal of physiology. Regulatory, integrative and comparative physiology, 313(4), R347–R356. doi.org/10.1152/ajpregu.00067.2017

D’Anci, K. E., Watts, K. L., Kanarek, R. B., & Taylor, H. A. (2009). Low-carbohydrate weight-loss diets. Effects on cognition and mood. Appetite, 52(1), 96–103. doi.org/10.1016/j.appet.2008.08.009