Your body can handle very little sugar at once. Your bloodstream carries less than 5 grams of glucose at any moment. That is under 1 1/2 teaspoons, or about 20 calories. Glycogen stores hold only about 100 grams in the liver and 400 grams in muscle. Insulin moves the excess into fat.
We have very limited room to store glucose, either as glycogen or as glucose in the blood. Glycogen: Glycogen is a large branched chain of glucose. It is stored mainly in the liver and in skeletal muscle. Stored glycogen can be turned back into blood glucose during fasting. It can also feed the muscle cells when muscles contract. This process is called glycogenolysis. In a fasted healthy 70kg human, the body can store 100 g of glycogen in the liver and 400 g in the muscle. Glycogen reserves can supply approximately 2,000 calories in total. Circulating glucose: Our blood normally carries less than 1 1/2 teaspoons of glucose at any given time (less than 5 g of glucose circulates in the blood of a 70kg human). Circulating glucose can supply 20 calories in total. The exact circulating glucose math: Average blood volume for an adult is 70ml/kg. Assuming a 70kg male=4,900 ml=49 dl or 4.9l 1 liter is 10dl, therefore we have 50dl. A nondiabetic glucose concentration is <100mg/dL. Therefore 100mg/dl multiplied by 49dl equals 4900mg of circulating glucose. 4900mg equals 4.9 g of circulating glucose, where each tsp =4.2gm Total circulating glucose=1.16tsp As a comparison, 1 gummy bear contains 1.3g of usable sugar. Eating 4 gummy bears could double the glucose in your blood. That doesn’t happen only because insulin quickly moves the glucose out of the blood and into fat stores. We have nearly unlimited room to store fat. The main job of insulin is to pull glucose out of the blood and turn it into stored fat. Glucose in the blood oxidizes fast. It goes through a non-enzymatic Maillard reaction. That causes spontaneous glycation (sugar sticking to proteins), which we measure as HbA1c. The Maillard reaction was first used to describe the browning and crisping of bread. This glycation effect makes cell membranes less fluid. It gets in the way of proteins and enzymes, and it often bends receptors and channels out of shape. The end result of too much glucose is sticky cells that do not work. Other advanced glycation end-products are measured as fructosamine. When blood glucose goes above 180 mg/dl, the kidney quickly flushes the extra out. That causes too much urination, or polyuria. The body keeps tight control of glucose because it can quickly oxidize and damage cell walls. That wreaks havoc on our enzyme pathways. What is glycemic index? The GI gives a score to how fast glucose from a certain food enters the blood. Foods are ranked on a scale of 0 to 100, with glucose at 100. The lower a food’s glycemic index, the slower blood sugar rises after you eat it. In general, cooking and processing a food raises its GI. The higher the GI of a food, the more insulin is released. And so the more blood glucose is turned into stored fat. How fast glucose rises after a meal, and how high it peaks, is often expressed as Glycemic Index (GI). Glycemic load (GL) measures two things: how fast glucose enters the blood (GI) and how much glucose is in each serving. Glycemic Load (GL) is a calculated number. It gives a patient a better idea of how a food acts at its usual serving size. Watermelon has a high glycemic index of 80. But a serving of watermelon has so little carbohydrate that its total glycemic load is only 5. When glucose levels drop, insulin production drops too. Then stored fat is turned into ketone bodies and triglycerides in the blood. Ketone bodies are a fuel source, like glucose, but they do not need insulin to get into the cells. The point is this: our blood can hold very little glucose, only about 5g or about 20 calories. Our constant eating of processed, carb-rich food clashes with how the human body works. The body tries to pull glucose out of the blood fast to prevent tissue damage. The constant high load in time overwhelms our ability to clear it. That leads to metabolic inflammation, and in the end diabetes. Wasserman D. H. (2008). Four grams of glucose. American journal of physiology. Endocrinology and metabolism, 296(1), E11-21. 10.1152/ajpendo.90563.2008
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Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP
Interventional pain physician, addiction medicine specialist and obesity medicine diplomate.
Licensed in Missouri and Illinois.
Last reviewed June 18, 2026
