The Functions Of Glucose In The Human Body: The Main Sources, The Norm In The Blood

Marko Balašević Author: Marko Balašević Time for reading: ~18 minutes Last Updated: August 28, 2022
The Functions Of Glucose In The Human Body: The Main Sources, The Norm In The Blood

The article talks about what glucose is, how it is absorbed into the body and what products can help maintain its normal level.

In the article we will tell:

  1. What is glucose and why is it needed
  2. Transformation of glucose in the body
  3. Hormonal regulation of blood glucose levels
  4. How much glucose per day
  5. What is the normal blood glucose
  6. What foods contain glucose
  7. Symptoms of low glucose
  8. What are the dangers of high blood glucose

What is glucose and why is it needed

Glucose is the main source of energy, fuel for the normal functioning of all organs and systems of the body, an essential component of metabolic processes.

Glucose has many names - simple sugar, grape sugar, monosaccharide. But first of all, glucose is a carbohydrate.

Carbohydrates are the most common class of organic compounds in nature. They perform many functions, but the main one is the source of energy.

What are carbohydrates?
  1. "Simple":

    • Monosaccharides are the simplest form of carbohydrates, they consist of 1 molecule and cannot be broken down into smaller units. Examples of monosaccharides are glucose, galactose, fructose.
    • Oligosaccharides are carbohydrates that contain 2-10 identical or different monosaccharide molecules. For example: sucrose (“food sugar”, found in sugar beets and cane, carrots, pineapples, sorghum), maltose (in malt, cereal sprouts), lactose (milk sugar, found in milk).


  2. "Complicated":

    • Polysaccharides are carbohydrates that contain more than 10 monosaccharide molecules. For example, starch (found in cereals, potatoes, legumes, vegetables), cellulose (in bran, vegetable peel), lignin (cereals, stale vegetables), glycogen (“animal starch”, synthesized in the liver, practically does not come from food), pectin (in berries and fruits), inulin (in the roots of dahlias, artichokes, dandelions).



Depends on the type of carbohydrates:

  1. whether enzymes are needed for their assimilation;

  2. with what speed they are soaked up - come to blood. Hence the division into “fast” and “slow” carbohydrates;

  3. who consumes carbohydrate - organs and systems or intestinal microflora;

  4. the level of insulin release in response to carbohydrate intake;

  5. metabolic features associated with carbohydrate intake.

Glucose, as a monosaccharide, is characterized by the following features:

  • sweet taste;
  • enzymes are not required for the digestion of glucose in its pure form;
  • glucose absorption occurs in the oral cavity and small intestine;
  • fast absorption rate;
  • causes a sharp rise in insulin;
  • is a source of energy for organs and tissues;
  • after consumption of glucose, hunger quickly sets in;
  • excess glucose is deposited in fat;
  • has a high glycemic index.

Carbohydrates, getting into the body with food, cause an increase in the levels of insulin and glucose in the blood. There are several indexes to evaluate them.

The glycemic index (GI) is a measure of how quickly glucose enters the bloodstream. The higher it is, the faster glucose enters the bloodstream, which means that the faster the level of glucose and insulin in the blood will rise. The glycemic index scale is based on glucose - its GI is 100.

Glycemic load (GL) - evaluates not the rate of increase in blood glucose levels, but the number of units by which its level will rise after eating a certain amount of a particular product. To calculate GL, the amount of carbohydrates in the product, the weight of the product and its GI are used.

For example, the GI of an apple is 38, in 100 gr. apple contains 13 gr. carbohydrates, which means that an apple has GN=38*13/100=5, i.e. glucose level after eating 100 gr. apples will increase by 5 units. This clearly demonstrates that the GI does not correspond to GN, and high GI foods may increase glucose levels slightly if they contain a small amount of carbohydrates per 100 g.

Insulin index - indicates the rate of insulin release in response to food intake, is considered together with the GI and does not always correspond to it. Any meal provokes the release of insulin, not just carbohydrate. The smallest - AI in foods rich in fats.

It is important to take into account all these indicators - GI, GN and AI for those who have metabolic disorders - insulin resistance, prediabetes or diabetes. A healthy person does not need to calculate these indices and simply adhere to the principles of good nutrition.

Functions of glucose

All carbohydrates during digestion are broken down into monosaccharides - glucose, galactose or fructose. Glucose is the only source of energy that absolutely all cells can use, this is its main function. In addition to energy, the biological role of glucose is extensive. Some of its features:

  1. Participates in metabolic processes, acts as the most digestible energy resource.

  2. Supports the body's performance.

  3. Nourishes brain cells, improves memory, learning.

  4. Stimulates the work of the heart.

  5. Quickly satisfies the feeling of hunger.

  6. Relieves stress, corrects mental state.

  7. Accelerates the recovery of muscle tissue.

  8. Helps the liver to neutralize toxic substances.

The body will receive the required amount of glucose by default if there is a sufficient amount of carbohydrate food in the diet, for example, the basics of a healthy diet are vegetables and cereals. Even if at some point carbohydrate food is not enough to meet the increased needs of the body, the liver will come to the rescue and its ability to synthesize glucose from non-carbohydrate sources.

An excess of sugars in the diet does not provide "glucose for the brain", as you sometimes hear, but causes serious harm to health. Consuming too much glucose is dangerous for everyone, but especially at risk are children, the elderly, patients with impaired metabolism.


"TOP 15 Calcium-Rich Foods: A Daily Value That Will Help Your Body Absorb Calcium" Read More

Some of the negative effects of excess glucose in the diet lead to:

  • obesity
  • the development of thrombophlebitis;
  • overload of the pancreas;
  • the occurrence of allergic reactions;
  • an increase in cholesterol;
  • the appearance of inflammatory, heart diseases, circulatory disorders;
  • arterial hypertension;
  • damage to the retina;
  • diabetes mellitus;
  • endothelial dysfunction.

The amount of monosaccharide that has entered the body must be fully compensated by the consumption of calories for energy needs.

Transformation of glucose in the body

Glucose enters the body with the consumption of carbohydrates from food. Further, partly in the oral cavity, and mainly in the small intestine, glucose is absorbed - its entry into the blood from the digestive system.

Glucose absorption

The absorption of any substances occurs with the help of passive or active transport.

Passive transport is the transfer of substances from an area of ​​high concentration to an area of ​​low concentration without energy consumption. It can take the form:

  1. Free diffusion, when substances independently move through the cell membrane.

  2. Facilitated diffusion, when the transfer of substances through the membrane occurs with the help of carrier proteins.


Active transport is the transfer of substances by special carriers from an area of ​​low concentration to an area of ​​high concentration, using the free energy of the body. Depending on the type of energy used, there are:

  1. Primary active transport, which uses the energy of ATP, is the universal energy carrier in the cell.

  2. Secondary active transport, which uses the energy stored in the cell.

How is glucose absorbed?
  • at a high concentration of glucose and after a meal, glucose is absorbed by facilitated diffusion;
  • at low concentrations of glucose, its absorption proceeds by secondary active transport with the help of sodium, which acts as a carrier.

Over 90% of the absorbed glucose is delivered to the liver through the portal vein, and the rest is transported through the general circulation to other tissues. However, with abundant consumption of carbohydrates, glucose can be immediately transported to various organs and tissues, bypassing the liver.

Organs and tissues that use glucose are:

  1. Insulin-independent, the transport of glucose into which is carried out with the help of carrier proteins, without the participation of insulin, the pancreatic hormone responsible for regulating blood glucose levels. These include the brain, kidneys, intestinal mucosa, red blood cells, gonads, placenta, lens of the eye. The supply of glucose to them does not change depending on the level of insulin.

  2. Insulin-dependent, the transport of glucose in which is carried out under the action of insulin. These include muscles (skeletal and heart), adipose tissue. With a decrease in insulin levels or insulin resistance, the supply of glucose to them is disturbed, they are left without energy, “starve”, and glucose itself remains in the blood.

Entering the cells of organs and tissues, glucose first of all turns into glucose-6-phosphate, which, unlike glucose, cannot penetrate the cell membrane. That is, this form of glucose is needed in order to “lock” glucose in the cell. Glucose-6-phosphate goes to glycogen biosynthesis, enters into glycolysis reactions or is broken down to glucose.


All processes of obtaining energy by living organisms occur as a result of redox reactions, in which an electron is transferred from one molecule (reductant, electron donor) to another (oxidizer, electron acceptor). In this case, either organic molecules or oxygen play the role of an oxidizing agent.

Glycolysis is a sequence of reactions associated with the oxidation of glucose, leading to its conversion into pyruvate (pyruvic acid, an important element for metabolic reactions) with the simultaneous formation of ATP. In this case, the glucose molecule is split into 2 pyruvate molecules, forming 2 ATP molecules and 2 NADP molecules (a coenzyme of several enzymes).

Glycolysis happens:

  • Aerobic, occurs with the participation of oxygen. In this case, pyruvate and NADP reach the mitochondria, where they are completely oxidized to carbon dioxide and water.
  • Anaerobic, occurs in conditions without oxygen supply. In this case, lactate (lactic acid) or ethyl alcohol is formed from pyruvate and NADP. This is the only way in conditions without oxygen that allows cells to receive energy. Anaerobic glycolysis occurs in muscles during intense exercise, when the circulatory system does not have time to supply the muscles with sufficient oxygen.

If glucose enters the body in excess, it is converted to glycogen in the liver and muscles. In an adult, its amount cannot exceed 450 g, a third of which is stored in the liver, the rest in the muscles.

Glycogen in the liver is used as a reserve source, a store of glucose in case of a decrease in its level between meals. After 10-18 hours without glucose from food, glycogen stores in the liver are depleted, and after 24 hours they are completely exhausted. Muscle glycogen is a source of energy during muscular work.

If glycogen stores are already high enough, glucose begins to turn into fat.


Some tissues and organs, such as the brain and red blood cells, depend on a constant supply of glucose. In this case, the liver can synthesize glucose from other monosaccharides, and when glycogen stores are depleted and there is a complete absence of carbohydrates in food, for example, during starvation or carbohydrate-free diets, the process of glucose synthesis from non-carbohydrate compounds - gluconeogenesis - starts. The starting compounds for it can be amino acids (primarily from muscle tissue), lactate, pyruvate, glycerols and fatty acids. Most glucose during gluconeogenesis is produced from lactate and amino acids. Through this process, tissues can go without an external source of glucose for several weeks.

Hormonal regulation of blood glucose levels

Fluctuations in the concentration of glucose in the blood, which are different from normal values, are perceived by the receptors of the hypothalamus - the region of the brain that regulates the constancy of the internal environment of the body. Due to the influence of the hypothalamus on the autonomic nervous system, there is an urgent increase or decrease in the production of hormones responsible for the regulation of blood glucose levels.

The level of glucose in the blood is lowered with the help of one hormone - insulin. An increase in blood glucose levels occurs under the action of several hormones: the pancreatic hormone glucagon; adrenal hormones; pituitary growth hormones and thyroid hormones.


"Ayurveda: what it is, what diseases it treats, the basics of nutrition according to Ayurveda" More

Insulin plays a key role in the regulation of carbohydrate metabolism. It stimulates the uptake of glucose by cells and its entry into the cell, activates its transport through cell membranes, accelerates the oxidation of glucose, enhances glycogen synthesis, and slows down gluconeogenesis.

Consequences of impaired insulin sensitivity:

  • destruction of muscle tissue;
  • decreased energy levels;
  • chronic inflammation;
  • an increase in the mass of visceral fat;
  • metabolic syndrome;
  • diabetes
  • cardiovascular diseases.
Hormones responsible for increasing glucose levels

An increase in blood glucose levels occurs under the action of several hormones. Glucagon is an insulin antagonist, produced by the pancreas, activates all processes leading to an increase in blood glucose concentration, accelerates the breakdown of glycogen and gluconeogenesis in the liver.


Adrenaline, an adrenal hormone, enhances glycogen mobilization.

Somatotropin, a growth hormone, increases the secretion of both glucagon and insulin, increases the deposition of glucose and enhances its utilization.

Cortisol, the stress hormone, accelerates gluconeogenesis and glycogen mobilization.

How much glucose per day

The average consumption of glucose in the body of an adult is 10 g/hour.

The main consumers of glucose:

  1. The brain needs about 60% of the total amount of glucose to ensure its work.

  2. Red blood cells take another 10-15% of all glucose.

  3. Muscles and adipose tissue, their needs are fickle and depend on activity.

Normally, the liver releases exactly the amount of glucose that covers the basic needs of the body (10 g / h), however, under the influence of glucagon or adrenaline, the liver can increase glucose output several times for a short time. About 30% of glucose is produced by the liver due to the breakdown of glycogen, and 70% - gluconeogenesis. The liver produces glucose at a rate equal to its utilization throughout the body.

It is difficult to calculate specifically the level of glucose consumption and, first of all, you need to start from the amount of carbohydrates. According to the norms of physiological needs for energy and nutrients for various groups of the population of the Russian Federation, it is recommended to receive no more than 60% of the daily energy requirement from carbohydrates, while simple sugars should account for no more than 10% of the total calorie content.

If your daily energy intake is 2000 kcal, then your carbohydrate intake is no more than 300 grams, while it is not recommended to consume more than 25 grams of added sugar. If you break this amount by type of carbohydrates, then the approximate norm per day is 210 grams. for complex carbohydrates, 40 gr. for fiber, 25 gr. for fructose, 25 gr. for added sugar. These figures are approximate and depend on the needs of a particular person and the characteristics of his body.

What is the normal blood glucose level?

Glucose is the only source of energy that absolutely all cells can use and is available to tissues in an almost constant concentration in the form of “blood sugar”. A constant level of glucose in the blood is needed to meet the various needs of the body. The brain is most sensitive to lowering glucose levels. According to the WHO guidelines established in 1999, the normal blood glucose level ranges from 3.3 mmol/l to 5.5 mmol/l. Moreover, at the moment, the upper value of 5.9 mmol / l is also accepted as the norm. At the same time, a level of no higher than 4.7-4.9 mmol / l is considered a healthy optimum. If there are suspicions of violations of carbohydrate metabolism, then in addition to the level of glucose in the blood, you need to rely on other indicators. First of all - glycated hemoglobin, insulin and the HOMA index.

Blood glucose levels fluctuate throughout the day and depend on many factors. First of all - from meals and from the state of health.

Between meals, the concentration of glucose in the blood is about 5 mmol / l (0.9 mg / l). Immediately after a meal, the glucose concentration rises to 7-8 mmol / l, and with a sufficiently long fasting it decreases to 4 mmol / l.

Experimental tests on the tolerance of glucose taken show that in healthy people, after taking 100 g. easily digestible carbohydrates, the blood sugar level rises, and after 2-3 hours it again decreases to its original level. In diabetic patients, the level of glucose after a meal rises more strongly, and decreases much more slowly.

What foods contain glucose

The source of glucose in food is carbohydrates, glucose is found in any carbohydrate food. If we adhere to the division into “fast” and “slow” carbohydrates, which demonstrates the rate of absorption of glucose, then the sources can be divided into 2 parts:

Sources of “slow” carbohydrates: cereals, legumes, vegetables, fruits, bread made from rye or whole grain flour - all those foods that, in addition to carbohydrates, contain fiber, vitamins, trace elements, and vegetable protein. Their assimilation by the body occurs gradually, does not lead to a rapid jump in blood glucose and thus does not overload the pancreas.

“Fast” carbohydrates are found in pastries, sweets, confectionery, sugary juices and soda. They instantly saturate the blood with glucose, which causes the pancreas to secrete too much insulin at once - this can subsequently cause cells to become insensitive to it.


Most carbohydrates contain bread made from flour of the first and highest grade, any sweets of industrial production, a lot of glucose - 99.9 g for every 100 g - is in sugar. But as you know, eating a product is not enough, you need to learn it.

There are ways to increase and decrease the degree of absorption of carbohydrates.

Improves the absorption of carbohydrates:

  • high degree of grinding products (mashed potatoes, cream soups, etc.);
  • high long-term heat treatment (boiled vegetables, pasta);
  • removal of fiber (juice).

Slows down the absorption of carbohydrates:

  • consumption in conjunction with foods rich in fiber and / or fats;
  • cooking to al dente;
  • eating starchy foods chilled due to resistant starch.


"Magnesium in foods: daily value, deficiency symptoms" More

Symptoms of low glucose

Lack of glucose is called "hypoglycemia". This is not an independent disease, but a condition characterized by a decrease in blood sugar levels below normal values. For men - below 2.5-2.8 mmol / l, for women - below 1.9-2.2 mmol / l.

In a healthy person, the causes of hypoglycemia can be pregnancy, intense physical activity, prolonged fasting. The level of glucose in this case is quickly replenished at the expense of the body's reserves or after eating and does not have any negative consequences. However, such cases of hypoglycemia are extremely rare. Most often, hypoglycemia develops in various diseases and pathological conditions.

Symptoms of glucose deficiency depend on its severity and the true cause. Some of the symptoms:

  1. a sharp and strong feeling of hunger;

  2. muscle tremors;

  3. sweating;

  4. increased heart rate;

  5. increased blood pressure;

  6. anxiety;

  7. motor excitation;

  8. depressed mood or, conversely, a feeling of euphoria;

  9. tingling of the lips, tongue, fingertips;

  10. deterioration in concentration, coordination of movements;

  11. slurred speech;

  12. drowsiness.

The main causes of hypoglycemia:

  • errors in insulin therapy for diabetes - skipping meals, drinking alcohol, excessive physical activity, an overdose of insulin or other drugs;
  • endocrine disorders, the result of which is a deficiency of the hormones cortisol, thyroxine, somatotropin; hypothyroidism, etc.;
  • operations on the gastrointestinal tract, as a result of which the breakdown and absorption of carbohydrates is disturbed:
  • disturbances in the work of enzymes involved in the metabolism of carbohydrates (glycogen, fructose, galactose) and the subsequent violation of the conversion of glucose from other carbohydrates or the difficulty of its release from glycogen.

What are the dangers of high blood glucose

Elevated blood glucose is called "hyperglycemia" and is characterized by an increase in blood glucose concentration of more than 6.1 mmol / l. The causes of this condition can be stress, a high-carbohydrate diet, medication, as well as diseases of the endocrine system and internal organs.

The symptoms of hyperglycemia can vary depending on its cause.

Hyperglycemia can be suspected by the following signs:

  1. Dry mouth.

  2. Profuse urination.

  3. Muscle weakness.


Hyperglycemia can be caused by physiological and pathological factors.

Physiological include stress, excess carbohydrates in the diet, pregnancy. In these cases, the sugar level normalizes on its own and its correction does not require any intervention. A constantly high concentration of glucose has a detrimental effect on the walls of blood vessels, which can cause diabetes mellitus in the future. Compliance with the principles of good nutrition is an excellent way to prevent hyperglycemia and its consequences.

Pathological hyperglycemia may be due to problems with the endocrine system (diabetes, prediabetes, insulin resistance), diseases of the central nervous system and metabolic disorders. To normalize blood sugar levels for pathological causes, diet, medications (insulin, hypoglycemic agents), and treatment of the underlying disease are used.

The most common pathological causes of hyperglycemia:

  • diabetes mellitus, in which there is either a decrease in insulin production (type 1 diabetes mellitus) or an excess of insulin production and the development of resistance to it (type 2 diabetes mellitus);
  • other diseases of the endocrine system, accompanied by increased production of hormones that increase the concentration of glucose by influencing various stages of carbohydrate metabolism;
  • convulsive conditions;
  • organic lesions of the central nervous system;
  • liver failure;
  • severe diseases of the pancreas;
  • taking medications that affect blood sugar levels.
  1. Glucose is the most important source of energy necessary for the smooth functioning of the body.

  2. Absorption and assimilation of carbohydrates is a complex process. dependent on many factors.

  3. The body protects itself from a decrease in glucose intake using various mechanisms - it creates glucose reserves, synthesizes glucose from other sugars and non-carbohydrate compounds.

  4. Various hormones are responsible for the hormonal regulation of glucose levels, while insulin alone is responsible for lowering the level. and for the increase - a whole group of different hormones.

  5. Carbohydrates are the most important source of energy necessary for the smooth operation of all body systems. A nutritious diet that contains enough carbohydrates, healthy fats, protein and fiber is the foundation of health and adequate energy levels.

  6. Hypoglycemia and hyperglycemia can occur in healthy people, and then their correction does not require special action. If these conditions are the consequences of diseases, then it is necessary to control the level of glucose in the blood in accordance with the doctor's recommendations.


About | Privacy | Marketing | Cookies | Contact us

All rights reserved © ThisNutrition 2018-2023

Medical Disclaimer: All content on this Web site, including medical opinion and any other health-related information, is for informational purposes only and should not be considered to be a specific diagnosis or treatment plan for any individual situation. Use of this site and the information contained herein does not create a doctor-patient relationship. Always seek the direct advice of your own doctor in connection with any questions or issues you may have regarding your own health or the health of others.

Affiliate Disclosure: Please note that each post may contain affiliate and/or referral links, in which I receive a very small commission for referring readers to these companies.