Glycogen Storage in an Average Person
An average 70 kg adult stores approximately 400–500 grams of glycogen, which provides roughly 1,600–2,000 calories of stored energy.
Distribution of Glycogen Stores
The body's glycogen is distributed across three primary compartments, each serving distinct physiological functions:
Skeletal muscle glycogen: Approximately 300–400 grams, representing the largest glycogen depot and utilized exclusively during muscle contraction and high-intensity physical activity 1, 2
Liver glycogen: Approximately 100–120 grams, which serves primarily to maintain blood glucose levels during fasting periods and between meals 1, 3
Minor stores: Small amounts are present in brain, heart, kidney, adipose tissue, and erythrocytes, though their specific functions remain largely unknown 1
Caloric Value and Storage Capacity
Each gram of glycogen provides approximately 4 calories when metabolized, yielding a total energy reserve of 1,600–2,000 calories from the combined liver and muscle stores 2
The maximum glycogen storage capacity in humans is approximately 15 g/kg body weight, meaning a 70 kg person can store up to 1,050 grams (4,200 calories) when glycogen stores are fully saturated through carbohydrate overfeeding 2
Under normal physiological conditions, glycogen stores accommodate approximately 500 grams before the body shifts to net lipid synthesis as the primary storage mechanism for excess carbohydrate 2
Physiological Context and Clinical Relevance
Brain glucose requirements: The brain requires 100–120 grams of glucose daily as its primary metabolic fuel, which can be supplied from hepatic glycogen breakdown or gluconeogenesis when exogenous glucose is unavailable 4
Glycogen hydration: Glycogen is stored in hydrated form with 3–4 parts water and associated potassium (0.45 mmol K/g glycogen), meaning the actual weight of glycogen stores including water is substantially higher than the dry glycogen mass 5
Depletion timeline: During fasting or very-low-calorie diets, hepatic glycogen stores are typically depleted within 24–48 hours, after which the body relies on gluconeogenesis from amino acids and glycerol to maintain blood glucose 4, 2
Common Pitfalls in Understanding Glycogen Storage
The rapid weight loss observed in the first few days of very-low-calorie diets (4–7 pounds) is primarily due to glycogen depletion along with its associated water weight, not true fat loss 5
Conversely, rapid weight regain after carbohydrate refeeding reflects glycogen and water restoration rather than fat accumulation, which can create misleading perceptions about diet effectiveness 5
Glycogen mobilization releases potassium and water, which can distort body composition estimates and overestimate nitrogen losses during dieting 5