Glucose is the fundamental building block of carbohydrates. It is frequently mentioned in the context of health, energy or diabetes, yet many people don’t realise just how vital it is to the body’s proper functioning.
Glucose is an important source of energy for most cells, including those in the brain. However, its level in the blood must be carefully regulated; both an excess and a deficiency can lead to fatigue, impaired concentration, and even the development of chronic conditions such as type 2 diabetes.
What is glucose, and what is its function in the body?
Glucose is a simple sugar (monosaccharide). It is the basic building block of many complex carbohydrates, which the body breaks down into glucose during digestion. Although it is sometimes discussed in a negative light, particularly in the context of high blood sugar, it is, in fact, a natural and essential substance for the body.
Basic properties
Glucose belongs to a group of carbohydrates known as hexoses, which are sugars that contain six carbon atoms. It is highly soluble in water and has a sweet taste. Naturally, it is found in fruits, vegetables, and honey, as well as in starchy foods. Alongside fructose (fruit sugar) and galactose (a component of lactose, or milk sugar), glucose is one of the three main simple sugars. While fructose is primarily metabolised in the liver, glucose acts as a universal energy source for most of the body’s cells.
Glucose as the main source of energy
The body uses glucose as its primary source of energy. Once it enters the bloodstream (known as blood glucose or “blood sugar”), cells absorb it through special transporters and convert it into ATP, which is the energy molecule that powers virtually all biological processes.
Glucose plays a special role in:
The brain - which is almost entirely unable to utilise fatty acids and depends heavily on a steady supply of glucose (or, in extreme cases, ketone bodies).
Red blood cells - which lack mitochondria and rely exclusively on glucose for energy via anaerobic glycolysis.
Muscles during exertion - where glucose provides a fast and accessible source of energy during physical activity.
Glucose storage in the body
When glucose is not needed immediately, the body stores it in the form of glycogen:
In the liver (about 80–100 g) - to help stabilise blood sugar levels between meals
In muscles (up to 300–400 g) - to provide a rapid energy reserve during physical activity
If glycogen stores are full and glucose intake continues, the excess glucose is converted to fat. However, this typically only occurs when carbohydrate consumption is consistently high.
Glucose in times of stress and starvation
The body is also capable of producing glucose on its own through a process called gluconeogenesis. In this process, glucose is synthesised from glucogenic amino acids, lactate, or glycerol. This is a vital mechanism during extended periods of starvation or physical stress, when maintaining glucose supply is crucial, even in the absence of food intake.
Gluconeogenesis also plays a key role during ketogenic or low‑carbohydrate diets, when the body must create glucose on demand to meet its needs.
How does glucose enter the body?
Glucose enters our bodies exclusively through food, specifically from the carbohydrates we consume every day, either knowingly (e.g., bread, pasta, fruit) or unknowingly (e.g., hidden sugars in highly processed foods).
Dietary sources of glucose
Most of the carbohydrates we ingest are in the form of:
Polysaccharides - such as starch, found in potatoes, rice, and cereals
Disaccharides - such as sucrose (table sugar) and lactose (milk sugar)
Monosaccharides - such as glucose and fructose, naturally present in fruit and honey
All of these carbohydrates are broken down during digestion into simple sugars, primarily glucose and fructose.
Digestion and absorption
The digestion of carbohydrates begins in the mouth, where the enzyme amylase breaks down starches into shorter chains. In the small intestine, other enzymes, such as maltase, lactase, and sucrase, whichfurther break down disaccharides into individual glucose and fructose molecules.
This is followed by absorption:
Glucose is transported through the wall of the small intestine into the bloodstream
From there, it enters directly into the liver, which either uses it, stores it as glycogen or sends it to other tissues
Glycaemic index and glycaemic load
The rate at which glucose enters the bloodstream after a meal depends on two key concepts:
Glycaemic Index (GI) - indicates how quickly a particular food raises blood glucose levels
Glycaemic Load (GL) - considers both the rate and the amount of carbohydrates in a typical serving
However, the glycaemic index can be influenced by several factors, including:
- The presence of fat and protein in the meal
- The amount of fibre from fruits, vegetables, or whole grains
- The cooking time and method used for carbohydrate‑rich foods
For example, while conventional rice has a high glycaemic index, its effect on blood sugar will be significantly reduced when paired with protein, fat, and vegetables.
Why is the absorption rate important?
A rapid rise in blood glucoseleads to a quick and large release of insulin, the hormone responsible for transporting glucose into cells
Blood glucose spikes can then lead to fatigue, hunger and sweet cravings
In contrast, slow absorption (e.g., with meals rich in fibre and protein) helps to maintain stable energy and satiety
Incremental hormones (GLP‑1, GIP) stimulate insulin release before glucose is absorbed
Regulation of blood glucose levels
Blood glucose levels, referred to as glycaemia, are tightly controlled in the body. And rightly so: too little glucose compromises basic brain function, while prolonged high levels can damage blood vessels, nerves and other tissues.
To maintain this delicate balance, the body relies on a complex hormonal network that constantly monitors how much glucose is circulating in the bloodstream, storing or releasing it as needed.
Normal blood glucose levels
Glucose levels are commonly measured when fasting or after meals:
| Status | Blood glucose level (fasting) |
| Normal | 4.0–5.6 mmol/l |
| Borderline (prediabetes) | 5.6–6.9 mmol/l |
| Diabetes mellitus (DM) | ≥ 7.0 mmol/l |
After a meal (postprandial), blood glucose levels may rise to 7.8 mmol/L, but they should return to normal within two hours. For long‑term blood sugar management, glycated haemoglobin (HbA1c)—sometimes referred to as the “long sugar”—is a more accurate indicator than fasting glucose alone.
Key hormones: insulin and glucagon
Glycaemic control is primarily managed by two hormones produced by the pancreas:
Insulin lowers blood glucose levels.
Released after a meal when glucose levels rise
Helps glucose enter cells (especially muscle and fat cells)
Promotes storage of glucose in glycogen (in the liver and muscles)
Glucagon increases blood glucose levels
Released when fasting or between meals
Activates glycogenolysis (breakdown of glycogen into glucose)
Triggers gluconeogenesis, the formation of glucose from other substances (amino acids, glycerol)
Other regulators
In addition to insulin and glucagon, several other hormones play supporting roles in blood sugar regulation:
Adrenaline and cortisol increase blood glucose during times of stress (known as stress hyperglycaemia)
Growth hormone (somatotropin) reduces the effect of insulin, especially during puberty or growth phases
Incremental hormones (GLP‑1, GIP) stimulate insulin release before glucose is absorbed
Where does glucose go after entering the bloodstream?
Once insulin is released, glucose is directed to several destinations:
Into the cellsf or immediate use as energy, especially by the brain, muscles, and red blood cells
To the liver and muscles where it is stored as glycogen
The body continuously balances glucose intake and utilisation to maintain homeostasis. Problems arise when cells become less responsive to insulin, a condition known as insulin resistance.
Hypoglycaemia (low blood sugar)
Hypoglycaemia refers to a condition where blood glucose levels fall below the normal range—usually below 4,0 mmol/l. It poses an acute threat to the body, as the brain is extremely sensitive to glucose and cannot quickly switch to another energy source. As a result, the body reacts swiftly and significantly to a sudden drop in blood sugar.
Symptoms of hypoglycaemia
Symptoms can be divided into two categories:
Autonomic (warning) symptoms:
Shivering, heart palpitations
Sweating
Hunger
Nausea, nervousness, restlessness
Neuroglycopenic symptoms:
Confusion, slowed thinking
Blurred vision
Weakness, dizziness
Speech disorders, loss of coordination
In extreme cases: unconsciousness or convulsions
The faster the glycaemia drops, the more dramatic the symptoms tend to be.
Causes of hypoglycemia
In healthy individuals, hypoglycaemia is rare in healthy people, but can occur, for example, in:
Prolonged fasting without adequate food intake
Intense physical activity without carbohydrate replenishment
Excessive alcohol consumption (especially when fasting)
In diabetics (especially those taking insulin or sulfonylurea derivatives), hypoglycemia is a common side effect:
Taking too high a dose of insulin
Skipping or delaying meals
Increasing physical activity without adjusting medication or food intake
First aid for hypoglycemia
The immediate goal is the rapid intake of simple sugar:
15–20 g of glucose or rapidly absorbed carbohydrates, e.g., 150 ml juice, 4–5 sugar cubes, glucose gel.
Re‑measurement of glycaemia in 10–15 minutes
If still low, repeat the process
Then follow with a more complex meal (carbohydrate + protein) to stabilise
For unconsciousness, inject glucagon or call for medical help.
Prevention of hypoglycaemia
Maintain a regular, balanced diet with adequate carbohydrates
Monitor and adjust insulin or antidiabetic medication carefully
Adapt treatment to changes in physical activity or eating patterns
For athletes: plan carbohydrate intake before and after exercise
Practice body awareness, especially crucial for people with diabetes who may not notice early warning signs
Hyperglycaemia (high blood sugar)
Hyperglycaemia refers to elevated blood glucose levels, usually above 7.0 mmol/L when fasting or above 11.0 mmol/L at any time of day. While a temporary rise in blood sugar can be a natural response to stress or illness, persistent hyperglycaemia is a serious health concern.
When and why does hyperglycaemia occur?
Hyperglycaemia can occur:
After meals high in sugar or starch – especially when the meal is poorly balanced (low in fibre, protein, or fat)
When there is insufficient insulin action: the body either does not produce insulin (type 1 diabetes) or does not respond to it properly (insulin resistance, type 2 diabetes)
During stress, illness or injury, the body releases stress hormones (cortisol, adrenaline) that raise blood glucose
When taking certain medications, e.g., corticosteroids
Acute and chronic effects
Short‑term hyperglycaemia:
Fatigue, drowsiness
Dry mouth, thirst
Frequent urination
Blurred vision
Impaired concentration
Chronic hyperglycaemia (e.g., in untreated type 2 diabetes) leads to damage to blood vessels and tissues due to:
Oxidative stress
Increased production of inflammatory substances
Glycation of proteins, which a process whereby proteins are damaged and their structure and function are altered
Risks of long‑term hyperglycaemia
With prolonged elevated glycaemia, the risk increases of:
Cardiovascular disease (atherosclerosis, heart attack, stroke)
Diabetic nephropathy (kidney damage)
Neuropathy (nerve damage causing tingling or numbness in the limbs)
Retinopathy (damage to the retina and risk of blindness)
Impaired wound healing and increased susceptibility to infections
Prediabetes and insulin resistance
Hyperglycaemia often begins before diabetes is officially diagnosed. This intermediate stage is known as prediabetes and is typically associated withinsulin resistance, meaning the body’s cells no longer respond effectively to insulin.
This stage is reversible. Through lifestyle changes, such as improving diet, increasing physical activity and managing stress, it's often possible to prevent the progression to type 2 diabetes and reduce the risk of complications.
How to reduce blood sugar levels
Elevated blood glucose levels—whether in the context of prediabetes or diagnosed diabetes—are not a cause for panic, but a call to action. The good news is that lifestyle plays a crucial role in glycaemic control. With targeted adjustments in diet, exercise, sleep, and stress management, many people can significantly improve their blood sugar levels, and some may even reverse the early stages of type 2 diabetes.
1. Maintaining a healthy amount of body fat (weight reduction)
The biggest risk factor for impaired glycaemia is excess body fat, especially around the abdomen (visceral fat). This type of fat is metabolically active and contributes directly to insulin resistance.
What helps:
Weight reduction by 5–10% of body weight can significantly improve insulin sensitivity and lower glycemia, even without other changes
The long‑term goal is fat reduction while preserving muscle mass
If you're feeling unsure, don’t hesitate to reach out to a specialist
2. Diet modification
It's all about nutrition. It’snot about extreme low‑carb diets, but about making smart, sustainable choices in the quality and timing of your carbohydrate intake.
Recommendations:
Limit simple sugars and ultra‑processed foods – white bread, pastries, fizzy drinks, and sweets
Increase fibre intake – vegetables, legumes, seeds, and whole grains slow glucose absorption and reduce post‑meal spikes
Include protein and healthy fats in every meal – to increase satiety and stabilise blood sugar
Smaller, regular meals – may be better tolerated by people with impaired glycaemia than large, infrequent meals
Watch your drinks – even juices, “healthy” smoothies and flavoured waters can be surprisingly high in sugar
3. Regular exercise
Physical activity allows muscles to directly use glucose from the bloodstream and also boosts their insulin sensitivity over time.
What works:
A short walk after meals – even just 10–15 minutes of brisk walking can help lower the post‑meal glucose spike
Strength training – builds muscle, which improves long‑term glucose uptake
Daily movement – informal activity like cleaning, walking, and standing is more beneficial than one hour at the gym, followed by a sedentary day
4. Quality sleep and stress management
Lack of sleep and chronic stress both increase levels of hormones that raise glycaemia (especially cortisol).
What helps:
Aim for 7–9 hours of sleep per night on a consistent schedule
Reduce blue light exposure and stimulating activities in the evening
Practice relaxation techniques – such as mindful breathing, meditation, or gentle yoga
Learn to pause and recharge during the day – to avoid cumulative exhaustion
Dietary supplements for better glycaemic control
In addition to diet, exercise, and sleep, certain dietary supplements can support better blood glucose control—especially in individuals with prediabetes or insulin resistance. While supplements are not a replacement for a healthy lifestyle, they can be a valuable complement to it.
Berberine
Berberine is a natural alkaloid that has shown a mild effect. It can improve insulin sensitivity, reduce fasting glycaemia and after meals and may promote modest weight loss in specific groups. It is particularly suitable for people with prediabetes or a mild form of insulin resistance. It is usually used at a dose of 500 mg 2‑3 times a day.
Cinnamon (Cinnamomum cassia or Ceylon)
Some studies suggest that cinnamon extract may improve cellular sensitivity to insulin and reduce postprandial glycemia. The effect is modest but may be beneficial as part of a comprehensive approach. With regular use, it is advisable to choose a more Ceylon cinnamon because of its lower coumarin content.
Psyllium
The soluble fibre from Indian plantain (psyllium) helps slow the absorption of carbohydrates from the diet, thereby reducing the postprandial rise in blood glucose. It also promotes satiety and contributes to healthy digestion. It is ideal to take it shortly before meals at a dose of 10g per day.
Myths and realities about glucose - Q&A
1. Is sugar toxic, and should it be completely avoided?
No, glucose itself is not toxic. It is an essential nutrient that the body needs for energy. The problem lies in excessive and frequent consumption of added sugars, especially in sweetened drinks, desserts, and processed foods. In small amounts, and as part of a balanced diet, added sugar is not harmful. What matters most is the amount, form, and frequency of intake.
2. Are natural sugars healthier than added sugars?
Chemically, there’s no meaningful difference—the glucose in a banana is the same as the glucose in table sugar.
However, the context matters:
- In fruit, sugar is paired with fibre, vitamins, antioxidants, and water, which slows absorption.
- In sweets and sugary drinks, sugar often comes with fat, minimal fibre, and high calories, making it more likely to cause blood sugar spikes.
It’s not that the sugar itself is “healthier,” but rather the whole food it comes in.
Bottom line
Glucose is essential for the human body, but in excess, especially alongside a sedentary lifestyle and high energy intake, it can lead to metabolic issues, insulin resistance, and chronic disease.
The goal is not to demonise sugar, but to understand how to manage it.
The key is to prioritise high‑quality, higher‑fibre carbohydrates, watch your overall energy intake, and maintain a healthy amount of body fat. Even modest weight loss often leads to significant improvements in glycaemia. Regular exercise (ideally after every meal), quality sleep and stress management also help.
It's not about extremes or prohibitions, but about long‑term balance and conscious habits that support healthy body function.
