Glycogen Stores

Glycogen is the body's primary stored-carbohydrate reserve: a branched polysaccharide of glucose molecules, stored in muscle cells and liver cells for rapid mobilisation when energy demand rises.

The two pools

• Muscle glycogen: 300–500 g in a typical trained adult. Locally held — muscle glycogen cannot return to the bloodstream as glucose; it can only be oxidised within the muscle where it's stored.
• Liver glycogen: 80–120 g. The liver's glycogen pool is the primary source of blood-glucose maintenance between meals — it is released as glucose to maintain normoglycemia during fasting.

The water-binding property

Each gram of stored glycogen is hydrated — bound with approximately 3 g of water. This is a meaningful mass:

• 500 g muscle glycogen + 3x water = 2,000 g (about 4.4 lb) stored in hydrated form.
• 100 g liver glycogen + 3x water = 400 g (about 0.9 lb).

Total glycogen-and-water mass: roughly 5 lb when fully stocked, 1–2 lb when substantially depleted. This is the mass signal that produces rapid weight shifts in low-carb or keto transitions and after hard training.

Depletion and repletion dynamics

• A single hard training session can deplete 30–50% of the trained muscle's glycogen.
• A 24-hour fast largely depletes liver glycogen; muscle glycogen stays relatively preserved unless exercise is added.
• Repletion after exercise: roughly 5–7% of depleted stores per hour with adequate carbohydrate intake; full repletion in 24–48 hours.
• Chronic low-carb or ketogenic diets maintain chronically lower muscle glycogen (typically 50–70% of a high-carb reference level). The body adapts by upregulating fat oxidation.

Why this matters for calorie tracking

Three tracking implications:

• Rapid weight loss at the start of a low-carb diet is glycogen + water, not fat. A 5 lb first-week drop in a keto transition is overwhelmingly water bound to depleted glycogen — a reliable, misreading trap.
• Refeed spikes are glycogen + water, not fat gain. A 3 lb bounce after a refeed is normal and flushes out over 3–5 days as glycogen normalises.
• "Stalled" weight after cardio increases is often partially glycogen-related. Adding a training block temporarily raises glycogen storage capacity; the associated water adds mass that masks fat loss for a week or two.

Performance implications

High-volume resistance training and any meaningful endurance work are glycogen-dependent. Chronically low glycogen reduces training quality: fewer reps at a given load, slower pace at a given heart rate, worse recovery between sessions. This is the main reason aggressive low-carb cutting impairs training performance for most trained lifters — and the reason refeeds and diet breaks (which partly replenish glycogen) often coincide with a noticeable training bump.

Glycogen and fat loss strategy

No direct connection: fat loss happens at the whole-body energy-balance level, not at the glycogen-depletion level. "Depleting glycogen to burn fat" is not a meaningful strategy — glycogen depletion just shifts fuel selection during and after exercise. Total fat loss over weeks depends on total caloric balance, not glycogen state.