Glycogen: Liver and Muscle Stores, Carbohydrate Loading and Water Weight

Glycogen is carbohydrate in storage: thousands of glucose units joined into a branched particle and packed inside muscle and liver cells. A review in Nutrition Reviews puts the average adult's store at about 500 g in muscle and about 80 g in the liver, and every gram is held with at least 3 g of water. It is a small reserve, yet it decides how long you can run hard and why the scale moves so quickly when carbohydrate is cut. This entry is part of the carbohydrates section of the handbook and follows on from the entry on glucose itself.

What is glycogen, and what is it for?

It is the form in which animals, people included, keep glucose for later. The Nutrition Reviews paper describes a particle built by two enzymes, one that links glucose units into strands and one that adds a branch every 8 to 12 units, and notes that a single liver particle can hold more than 50,000 glucose molecules. The branches matter because glucose can be clipped off many ends at once, which makes glycogen a fast fuel.

The two stores do different jobs. Liver glycogen belongs to the whole body: between meals the liver breaks it down and releases glucose to keep the roughly 4 g in the bloodstream topped up, mainly for the brain. Muscle glycogen is private. It is burned inside the muscle that holds it, and the same review calls it the primary fuel during exercise of moderate or greater intensity, even though liver and muscle glycogen together make up only about 4 per cent of the body's fuel reserves.

How much glycogen does the body hold?

About 580 g in an average adult, taking the two averages together, with a wide range around it. ICMR-NIN's Dietary Guidelines for Indians, 2024, counts carbohydrate at 4 kcal per gram, so a full store is worth roughly 2,300 kcal: about a day's energy for a sedentary adult, and far less than the body keeps as fat. That sum is NNWA's arithmetic on published averages, not a measurement of any one person. Muscle stores are larger in people with more muscle and in those who train.

The liver figure swings through the day. The printed range starts at zero because the store depends on the carbohydrate in the diet, the time since the last meal and recent activity. Muscle glycogen is steadier at rest: in trained, well-fed endurance athletes it sits at about 150 mmol per kg of muscle, can reach about 200 mmol per kg after a few days of rest on a high-carbohydrate diet, and can fall below 50 mmol per kg after prolonged intense exercise.

How long do glycogen stores last?

Liver glycogen covers a share of the body's glucose supply for roughly a day without food, and muscle glycogen lasts about two hours of steady hard effort. In a study that tracked liver glycogen by magnetic resonance through a 68-hour fast, new glucose made by the liver already supplied 64 per cent of glucose production in the first 22 hours, leaving about 36 per cent to glycogen. That share then shrank: new glucose supplied 82 per cent over the next 14 hours and 96 per cent in the final 18.

Muscle is emptied by work, not by time. Two hours or more of even moderate activity is enough to lower muscle glycogen markedly, and repeated near-maximal lifts in a gym session cut it by 25 to 40 per cent. A review in Sports Medicine found that in endurance events lasting more than 90 minutes, exhaustion usually coincides with critically low muscle glycogen. Refilling is slow: at least 24 hours of rest on a high-carbohydrate diet is needed to restore muscle glycogen fully.

The Indian guideline: how much carbohydrate keeps the stores filled

ICMR-NIN sets no requirement for glycogen, because the body makes it from the carbohydrate you eat. What the 2020 Nutrient Requirements for Indians does set is a minimum of 100 to 130 g of carbohydrate a day and an acceptable range of 45 to 65 per cent of energy for adults. At 2,000 kcal, 45 per cent works out to 225 g. For a sedentary or lightly active adult, an ordinary Indian plate of rice or roti, dal, vegetables and fruit keeps glycogen topped up with no special plan.

People who train hard are a separate case, and the figures for them come from sports nutrition bodies, not from ICMR-NIN. They are set per kilogram of body weight and rise with the training load. A recreational walker or yoga practitioner sits in the first row of the table below, and the Nutrition Reviews paper says normal eating is usually enough there.

The third column is arithmetic for one body weight; use the macro calculator for your own. In Indian food the carbohydrate comes mostly from cereals. By the Indian Food Composition Tables 2017, raw milled rice has 76.39 g of available carbohydrate per 100 g, whole-wheat atta 58.62 g, ragi 62.47 g, a ripe robusta banana 18.94 g and potato 11.79 g. NNWA's table of carbohydrate in Indian foods lists the rest.

What is carbohydrate loading, and who needs it?

It is a few days of very high carbohydrate eating with reduced training, used before long endurance events to start with muscle glycogen above its normal level. The International Society of Sports Nutrition's 2017 position stand says stores are maximised on 8 to 12 g of carbohydrate per kg a day, and that the older depletion phase can be skipped: cutting training for three to four days while eating 8 to 10 g per kg for one to three days is enough. It adds that women may need to raise total energy intake on loading days to match the effect seen in men.

Loading is a tool for trained people before a specific event. NNWA's Sports Nutrition course covers how it sits within a season's eating; the amounts above are far more carbohydrate than a sedentary adult needs on any day.

Why does weight fall so fast in the first week of a low-carb diet?

Mostly because glycogen leaves and takes its water with it. A biopsy study of nine trained adults cycling in the heat confirmed that each gram of muscle glycogen is stored with at least 3 g of water, and an earlier paper put the figure at three to four parts. When carbohydrate is cut sharply the stores shrink, the water is passed as urine, and the Nutrition Reviews paper notes that this quick loss subsides after a few days and reverses when the stores refill. The entry on the low-carbohydrate diet covers what happens over the following months.

One metabolic ward study measured it directly. Six obese adults spent ten days on each of two 800 kcal diets, one ketogenic and one with carbohydrate and fat in usual proportions. They lost weight much faster on the ketogenic diet, but the makeup of the loss was different, as the table shows.

The last row is the lesson. At the same energy intake, fat loss was practically identical, and the extra weight lost without carbohydrate was water. It was a small, short study in a hospital ward, but it explains a pattern many dieters see at home. The article on how much weight you can really lose sets realistic weekly figures, and the page on the Indian keto diet plan covers that diet itself.

What does the evidence say about glycogen and performance?

It says that starting with full stores helps in long events and makes little difference in short ones. The Sports Medicine review concluded that raising muscle glycogen above normal has little or no effect on all-out efforts under five minutes or on moderate exercise of 60 to 90 minutes, but postpones fatigue by about 20 per cent in events beyond 90 minutes and improves performance over a set distance by 2 to 3 per cent.

Day-to-day carbohydrate matters as well. In one study quoted in the Nutrition Reviews paper, 24 hours on 9.8 g of carbohydrate per kg restored 93 per cent of the muscle glycogen used in a two-hour ride, against 13 per cent on 1.9 g per kg. In another, race walkers who trained for three weeks on 8.6 g per kg improved their 10 km time by 6.6 per cent, while those on 2.1 g per kg did not improve.

A worked example: loading for a first marathon on Indian food

This is an illustrative case, not a real person. A 60 kg accounts manager in Bengaluru is running her first full marathon and plans two loading days at 8 g of carbohydrate per kg, which is 480 g a day. Using IFCT 2017 values for raw foods: 300 g of rice across three meals gives 229 g, 150 g of atta as rotis 88 g, four 100 g bananas 76 g, 300 g of potato 35 g, 50 g of dry dates 34 g and 25 g of jaggery 21 g. The total is 483 g.

Two things follow. First, the volume is large: nearly twice the 250 g of cereal in ICMR-NIN's model plate for a 2,000 kcal day, which is why fat and bulky vegetables are trimmed for those two days only. Second, suppose her stores rise by 150 g. With at least 3 g of water per gram, the scale would show 600 g or more on race morning. The 150 g is an assumption chosen to show the sum, not a prediction for her.

Common myths and mistakes about glycogen

The commonest mistake is reading the first week's weight loss as fat. On any diet that cuts carbohydrate, a quick drop of a kilo or two fits the arithmetic of glycogen and water: 400 g of glycogen with three times its weight in water comes to 1.6 kg. The reverse mistake is panic after a wedding weekend, when refilled stores add the same water back.

A third mistake is loading for a short event or an ordinary gym session, where the reviews find no benefit. A fourth is to assume that skipping breakfast or a day's fast empties the muscles. Short-term fasting lowers liver glycogen, but the Nutrition Reviews paper notes that it does not affect muscle glycogen, which is spent by exercise. NNWA's article on intermittent fasting in India looks at fasting on its own terms.

Cautions, and when to see a doctor

Glycogen itself is not something to supplement, and no upper limit applies to it. The cautions concern the two ways people try to move it. Loading at 8 to 12 g per kg is a very large carbohydrate intake, and cutting carbohydrate sharply changes blood glucose and fluid balance within days. Either can be unsafe for someone on glucose-lowering medicine, and neither is a way to manage a disease. The entry on insulin and insulin resistance explains the hormone that directs glucose into glycogen.

Learning this subject at NNWA

Energy stores, carbohydrate needs and the planning of diets for active people are taught at NNWA, a private skill academy in Kolkata whose classes run online in English and Hindi. Its courses, beginning with the Certification in Nutrition, prepare people to coach healthy clients and to refer medical cases to a doctor. None is a degree or a dietitian qualification.