Glycogen depletion- How not to exercise
What happens when we exercise or go on a restrictive diet? What is glycogen depletion and should we avoid it? Does glycogen depletion have any benefits?
Milos Pokimica
Written By: Milos Pokimica
Medically Reviewed by: Dr. Xiùying Wáng, M.D.
Updated May 29, 2023What happens when we exercise or go on a restrictive diet? What is glycogen depletion and should we avoid it? Does glycogen depletion have any benefits?
What happens to the body is that we go into fasting mode (not starving mode). It is a state that is completely different from starvation.
In the first stage, the body will burn readily available calories in the form of stored sugar glycogen. Same as fat our bodies have storage of ready-to-use sugar (glycogen) that is easily metabolized. It is quick energy that is available in an instant and unlike fat does not require any metabolic pathway. Our cells use glycogen directly.
Most of the sugar is stored primarily in the cells of the liver and the muscles, hydrated with water. When we start to burn more energy than we have available in the bloodstream our blood sugar level is going to drop. At the first stage as a countermeasure, our body is going to use an easily available source of stored energy or in other words stored glycogen. Because glycogen is hydrated with water inside the cells when we burn sugar water molecule is an excess or byproduct of metabolism. Because of that, we will lose some water weight in the first stage.
If you do not know this, you can be surprised when you go on a diet and lose water and be happy, to gain it all back after. Water loss released from glycogen and sodium is usually the culprit for dramatic first-week weight loss.
In the liver, glycogen reserves can build up to 5–6% of the organ’s flesh weight (100–120 grams in an adult). Muscles have a much lower concentration of glycogen, in the range of one to two percent of the total muscle mass.
The untrained individual holds typically about 400 grams of glycogen that is stored in the entire body, in both muscles and the liver. A trained professional athlete can hold double that amount. This amount of glycogen is enough to last for several hours of intensive exercise without replenishment.
When we train our body adapts, and the condition improves. Professional athletes also do something called carbohydrate loading after the exercises to force their bodies to adapt by increasing the storage capacity of intramuscular glycogen stores. There are some studies done on this. If we take caffeine or drink coffee glycogen stores tend to be replenished more rapidly.
Long-distance athletes often experience glycogen depletion. It is called “hitting the wall”. In professional sports, it has a powerful influence because after depleting sugar reserves, fatigue follows and sometimes to the point that it is difficult to move. This is the reason why you see athletes bonking. Bonking (Glycogen depletion) is not the state in which you are just feeling tired. Bonking is when your glycogen reserve stores get so low that your brain starts to run out of energy and then shuts your body down.
After the initial stage and metabolization of easily available reserves of glycogen, the liver will begin to break down fat and protein to form energy immediately. The problem is that this process takes time and until gluconeogenesis kicks in, an athlete may experience symptoms of hypoglycemia. If this happens, it will not be uncommon to see professional athletes collapse from extreme fatigue.

Hypoglycemia comes with dizziness, blurred vision, and hallucinations. Loss of consciousness may also occur under these conditions. The combined use of several different energy sources that allow extended high muscular power outputs that can be maintained for an extended period is a big deal in professional sports and research. Also, no we cannot go on a diet before the marathon to tap into gluconeogenesis and then run. Running a marathon using fat alone as a fuel source is not plausible. If we are able to metabolize fat at a higher rate then we would never become tired and could run indefinitely. The energy efficiency of fat metabolization, unfortunately, is not at that level.
Moreover, our body can only process a limited amount of carbohydrates per hour also, around 30-60 grams depending on individual efficiency. You probably won’t race a marathon, but it is essential to understand how the body works if you want to exercise, you can potentially do yourself damage, or don’t get the desired results.
In bodybuilding, it is a big deal also because catabolizing muscle mass for energy is not the desired course. After glycogen depletion from 16 hours to 72 hours, the body will lean heavily on amino acids and protein catabolism for energy creation. Amino acids will be used, and some of the muscle mass will be lost when going on a fast with or without exercise. We can try to minimize it, but some amino acids will be used for energy.
The loss of some of the tissue is not as bad as it sounds. It has an evolutional purpose and health benefits if done moderately. It is normal for all animals including humans to go into fasting mode periodically. Our bodies have adapted to fasting during evolution in the same way that we have adapted to physical activity. Moderate periodical fasting will help our body to clean its mutated and damaged precancerous cells in a process known as autophagy (self-eating). When there are two cells and one is damaged and one has to be destroyed for energy, the body will catabolize damaged cells first and thus clean itself in a sense. We will have a negative impact on our health if we do not incorporate exercise and fasting into our regular life.

After this initial period, our metabolism will shift to ketosis where it gets almost all of its energy from ketone bodies from fat metabolism. The basal metabolic rate will drop also, or in other words, the use of energy will become more efficient. If you want to diet this is a state you would want to be in. A permanent caloric deficit in the amount that you can handle. Running a marathon or doing extensive exercise in a fast state might not be so beneficial because our brain will be left without food and will be forced to use our own muscle tissue for energy. This is not the desired outcome.

- Feeding – Insulin levels rise during meals. This allows glucose to be absorbed into tissues such as the muscle or brain and used directly for energy. Excess glucose is stored in the liver as glycogen.
- The post-absorptive phase occurs 6-24 hours after fasting begins. Insulin levels begin to drop. Glycogen breakdown produces glucose for energy. Glycogen stores last about 24 hours.
- Gluconeogenesis can take anywhere from 24 hours to 2 days. In a process known as “gluconeogenesis,” the liver creates new glucose from amino acids. This literally translates as “creating new glucose.” Glucose levels in non-diabetics fall but remain within the normal range.
- Ketosis – 2-3 days after fasting begins – The low insulin levels reached during fasting promote lipolysis or the breakdown of fat for energy. Triglycerides, the fat storage form, are composed of a glycerol backbone and three fatty acid chains. Glycerol is used in the process of gluconeogenesis. Many tissues in the body can use fatty acids directly for energy, but not the brain. Ketone bodies, which can cross the blood-brain barrier, are synthesized from fatty acids and used by the brain. Ketones provide approximately 75% of the energy used by the brain after four days of fasting. The two major types of ketones produced are beta-hydroxybutyrate and acetoacetate, both of which can increase by more than 70 percent during fasting.
- Protein conservation phase. High levels of growth hormone help to keep muscle mass and lean tissues in check. The energy required to maintain basal metabolism is almost entirely supplied by free fatty acids and ketones. Increased norepinephrine (adrenaline) levels prevent the metabolic rate from decreasing.
The human body has well-developed mechanisms for dealing with hunger. In essence, what we are describing here is the process of transitioning from burning glucose to burning fat. That is it. Fat is simply stored food energy in the body. When there is a scarcity of food, stored food is naturally released to fill the void. So, no, the body does not ‘burn muscle’ to feed itself until all fat stores are depleted. There will be some catabolism at acceptable levels if you don’t have diabetes. In situations where there is hypoglycemia for survival, our body will burn everything to preserve brain cells from dying. If you don’t have hypoglycemia then no the body will not burn muscle but fat.
We can last for a period of 2.5 to 3 months just drinking water depending on how much fat we have to begin with. If we have large amounts of fat, we can last much longer, but nutrient deficiencies will occur. Because of this reason low-calorie nutrient-dense, whole fiber-rich food is a base for every diet.
A good example of this is a man named Angus Barbieri, who water fasted for an entire year under medical supervision study (Stewart et. al, 1973). He was given vitamin supplements only. No calories, no protein.

References:
- Murray, B., & Rosenbloom, C. (2018). Fundamentals of glycogen metabolism for coaches and athletes. Nutrition reviews, 76(4), 243–259. https://doi.org/10.1093/nutrit/nuy001
- Impey, S. G., Hearris, M. A., Hammond, K. M., Bartlett, J. W., Louis, J., Close, G. L., & Morton, J. P. (2018). Fuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis. Sports Medicine, 48(5), 1031–1048. https://doi.org/10.1007/s40279-018-0867-7
- Stewart, W. K., & Fleming, L. W. (1973). Features of a successful therapeutic fast of 382 days’ duration. Postgraduate medical journal, 49(569), 203–209. https://doi.org/10.1136/pgmj.49.569.203
Related Posts
Do you have any questions about nutrition and health?
I would love to hear from you and answer them in my next post. I appreciate your input and opinion and I look forward to hearing from you soon. I also invite you to follow us on Facebook, Instagram, and Pinterest for more diet, nutrition, and health content. You can leave a comment there and connect with other health enthusiasts, share your tips and experiences, and get support and encouragement from our team and community.
I hope that this post was informative and enjoyable for you and that you are prepared to apply the insights you learned. If you found this post helpful, please share it with your friends and family who might also benefit from it. You never know who might need some guidance and support on their health journey.
– You Might Also Like –

Learn About Nutrition
Milos Pokimica is a doctor of natural medicine, clinical nutritionist, medical health and nutrition writer, and nutritional science advisor. Author of the book series Go Vegan? Review of Science, he also operates the natural health website GoVeganWay.com
Medical Disclaimer
GoVeganWay.com brings you reviews of the latest nutrition and health-related research. The information provided represents the personal opinion of the author and is not intended nor implied to be a substitute for professional medical advice, diagnosis, or treatment. The information provided is for informational purposes only and is not intended to serve as a substitute for the consultation, diagnosis, and/or medical treatment of a qualified physician or healthcare provider.NEVER DISREGARD PROFESSIONAL MEDICAL ADVICE OR DELAY SEEKING MEDICAL TREATMENT BECAUSE OF SOMETHING YOU HAVE READ ON OR ACCESSED THROUGH GoVeganWay.com
NEVER APPLY ANY LIFESTYLE CHANGES OR ANY CHANGES AT ALL AS A CONSEQUENCE OF SOMETHING YOU HAVE READ IN GoVeganWay.com BEFORE CONSULTING LICENCED MEDICAL PRACTITIONER.
In the event of a medical emergency, call a doctor or 911 immediately. GoVeganWay.com does not recommend or endorse any specific groups, organizations, tests, physicians, products, procedures, opinions, or other information that may be mentioned inside.
Editor Picks –
Milos Pokimica is a doctor of natural medicine, clinical nutritionist, medical health and nutrition writer, and nutritional science advisor. Author of the book series Go Vegan? Review of Science, he also operates the natural health website GoVeganWay.com
Latest Articles –
Plant Based News
-
‘I Tried The Viral Tofu Pancakes With 30g Of Protein’
on May 2, 2025
-
Eat Just Launches Single Ingredient Vegan Protein Powder At Whole Foods Market
on May 2, 2025
-
How To Make Girl Scout Cookie-Inspired Vegan Thin Mints
on May 2, 2025
-
Beyond Steak Makes UK Debut At Hundreds Of Tesco Stores Nationwide
on May 2, 2025
-
Vegan Loaded Focaccia Slab
on May 2, 2025
-
2 Weeks of Vegan Eats In Los Angeles and Las Vegas
on May 1, 2025
-
Study Finds No Difference In Muscle Fiber Protein Synthesis Between Vegan And Omnivore Diets
on May 1, 2025
Top Health News — ScienceDaily
- Process driving evolution and major diseaseson May 2, 2025
The only remaining autonomous ‘jumping gene’ can only attach to, and stitch a copy of itself into, DNA when it builds up into large clusters and only as cells divide.
- New gene-editing therapy shows early success in fighting advanced GI cancerson May 2, 2025
Researchers have completed a first-in-human clinical trial testing a CRISPR/Cas9 gene-editing technique to help the immune system fight advanced gastrointestinal (GI) cancers. The results show encouraging signs of safety and potential effectiveness of the treatment.
- The all-female Korean Haenyeo divers show genetic adaptions to cold water divingon May 2, 2025
The Haenyeo, a group of all-female divers from the Korean island of Jeju, are renowned for their ability to dive in frigid waters without the aid of breathing equipment — even while pregnant. A study shows that the divers’ remarkable abilities are due to both training and genetic adaptation, including gene variants associated with cold tolerance and decreased blood pressure. The divers also showed pronounced bradycardia, or slowing of the heart rate, when they dived, but this trait is likely […]
- Antivenom neutralizes the neurotoxins of 19 of the world’s deadliest snakeson May 2, 2025
By using antibodies from a human donor with a self-induced hyper-immunity to snake venom, scientists have developed the most broadly effective antivenom to date, which is protective against the likes of the black mamba, king cobra, and tiger snakes in mouse trials. The antivenom combines protective antibodies and a small molecule inhibitor and opens a path toward a universal antiserum.
- Everyday actions and behaviors linked to better mental well-being: Studyon May 2, 2025
Regular chats with friends, time spent in nature and mentally engaging activities are strongly linked to better mental health, according to new research that highlights the power of simple, everyday behaviors to improve well-being.
- The secret to happiness lies within you, or society — or bothon May 2, 2025
What is the secret to happiness? Does happiness come from within, or is it shaped by external influences such as our jobs, health, relationships and material circumstances? A new study shows that happiness can come from either within or from external influences, from both, or neither — and which is true differs across people.
- Is your heart aging too fast?on May 2, 2025
Researchers have developed a revolutionary new way to find out the ‘true age’ of your heart using MRI. A new study shows how an MRI scan can reveal your heart’s functional age — and how unhealthy lifestyles can dramatically accelerate this figure. It is hoped that the findings could transform how heart disease is diagnosed — offering a lifeline to millions by catching problems before they become deadly. The team say their cutting-edge technique is a ‘game changer’.
PubMed, #vegan-diet –
- Vegan beware! Allergenic potential of legumeson April 30, 2025
CONCLUSION: The increased consumption of legumes in the context of a vegan diet is bringing a wider range of plant-based foods into focus, which may have potentially allergenic properties. An increase in allergic reactions to legumes is to be expected. Precise molecular IgE diagnostics are crucial to be able to assess the risk of severe reactions.
- Body and Fitness-related Shame Helps Explain the Association Between Internalized Weight Bias and Orthorexia Symptoms among North American Female Yoga Professionalson April 30, 2025
CONCLUSIONS: Findings contribute to the growing scholarship recognizing orthorexia’s links with harmful diet culture among yoga professionals potentially reflecting: 1) regulating internal body- and fitness-related shame stemming from IWB and 2) perceptions of modeling “positive” body image for students and clients who may be at risk. Results call for increased collaborative outreach efforts to identify appropriate interventions to effectively target these public health concerns within the…
- Desensitization for Vitamin B12 Hypersensitivity and How to Do Iton April 29, 2025
Vitamin B12 is the common name for a group of cobalamins, which are cobalt corrines. Cobalamins are water-soluble B vitamins. Vitamin B12, as a coenzyme of various enzymes, is an essential component of many key metabolic processes in the body. Vitamin B12 deficiency causes dysfunction of various organs and systems in the body, including the central nervous system. Humans, like other animals, are unable to synthesize cobalamin. This vitamin must be supplied with a balanced diet. The only […]
- Effects of lacto-vegetarian and vegan diets on glycemic responses and metabolite profiles in healthy adults: A randomized trial using continuous glucose monitoring and targeted metabolomicson April 29, 2025
CONCLUSIONS: Our pilot CGM data suggest a lacto-vegetarian diet may offer better glycemic control, potentially explained by our preliminary metabolomics findings. The increased Phe observed in the vegan group may be explained by a hypothetical mechanism in which higher glucose induces oxidative stress, whereas the increased C2 from dairy in the lacto-vegetarian group may protect against oxidative stress, contributing to lower glucose concentrations. However, larger, longer-term studies with […]
- The Carbon Footprint of Diets with Different Exclusions of Animal-Derived Products: Exploratory Polish Studyon April 26, 2025
Background/Objectives: Analyzing the carbon footprint of diets in various populations is important as it can help identify more sustainable food choices that reduce the overall impact of human activities on ongoing warming of the global climate. This pilot exploratory study analyzed the carbon footprint (measured in kg of CO(2) equivalent, eq.) using food diaries collected from Polish individuals with varying levels of animal-derived product exclusion in their diets. Methods: The study […]
Random Posts –
Featured Posts –

Latest from PubMed, #plant-based diet –
- Association between plant-based diets and depression in older adults with heart disease: the mediating role of sleep disturbancesby Yaqun Yu on May 1, 2025
CONCLUSION: This is the first study to suggest a significant negative relationship between plant-based diets and depression in older adults with heart disease. Sleep quality plays a mediating role in the association between plant-based diets and depression. Optimizing the dietary structure and improve sleep quality may help reduce the risk of depression in older adults with heart disease.
- A comparative study of the EAT-Lancet diet and the Mediterranean diet in relation to neuroimaging biomarkers and cognitive performanceby Jessica Samuelsson on April 30, 2025
BACKGROUND: The impact of the sustainable EAT-Lancet planetary health diet on brain and cognitive health remains unclear. This study compared the impact of the EAT-Lancet diet with the well-established cognitive-beneficial Mediterranean diet (MeDi) in relation to neuroimaging biomarkers and cognitive performance among older adults.
- Investigating the Effects of Arabidopsis thaliana Cruciferin Double Knockouts on Amino Acid Profiles, Dry Seed Proteome, and Oxidative Stress Levelsby Clement Bagaza on April 30, 2025
As plant seeds mature, they accumulate large quantities of seed storage proteins, which are a vital source of carbon, nitrogen, and sulfur necessary for establishing the seedling, especially during the transition from the heterotrophic to the photoautotrophic stage. However, seed storage proteins in many crop seeds are deficient in essential amino acids, which cannot be synthesized by humans and monogastric animals and must be obtained from the diet. Lysine and tryptophan are the most […]
- Vegan beware! Allergenic potential of legumesby Jil Marie Jubel on April 30, 2025
CONCLUSION: The increased consumption of legumes in the context of a vegan diet is bringing a wider range of plant-based foods into focus, which may have potentially allergenic properties. An increase in allergic reactions to legumes is to be expected. Precise molecular IgE diagnostics are crucial to be able to assess the risk of severe reactions.
- Nitrogen additive with extruded urea with essential oils to control gastrointestinal worms in lambsby Fernanda Grazielly Gomes de Oliveira on April 30, 2025
Our objective was to evaluate the effect of a nitrogen additive with extruded urea with essential oils based on garlic and cinnamon on the resistance to gastrointestinal worms and on the performance of lambs in the finishing phase. Fourteen male sheep were used, with an average age of 18 months and an average initial body weight of 23.5 kg. The lambs were divided into two nutritional treatments: control and nitrogen additive. The control treatment was composed of a roughage: concentrate ratio […]
- Diversity in Chilean Bean Varieties: Effects of Water Cooking on Nutrition and Culinary Qualityby Sergio-Miguel Acuña-Nelson on April 30, 2025
In this study, we conducted a comprehensive analysis of various Chilean bean varieties, examining how cooking influences their nutritional and culinary characteristics. We found that these varieties exhibit significant differences in their protein, lipid, ash, fiber, and carbohydrate profiles in both raw and cooked states. Generally, cooking tends to increase proteins and carbohydrates while decreasing lipids and ashes, although these changes vary depending on the variety. The importance of…