In a world where nutritional information is often contradictory, simple sugars are at the centre of controversy. This is especially true for fructose and glucose, two monosaccharides with a similar chemical structure but surprisingly different effects on the body. Why can one of them accelerate the ageing process? How does glycation affect our tissues? And what does all this mean for our everyday food choices?
The fundamental difference: fructose and glucose metabolism
Although fructose and glucose have the same chemical formula (C₆H₁₂O₆), their spatial structure and the way they are processed by the body differ significantly.
Glucose: the basic cellular fuel
Glucose is the most common ‘fuel’ for our cells. After consumption:
- It triggers the secretion of insulin from the pancreas
- It is metabolised in almost all body tissues
- Its level in the blood is strictly regulated by the endocrine system
- Excess is stored as glycogen in the liver and muscles
Fructose: a problematic sweetener
Although fructose occurs naturally in fruit, it mainly enters our diet in large quantities through the addition of glucose-fructose syrup to food. After consumption:
- It does not stimulate insulin or leptin (the satiety hormone) secretion.
- It is metabolised almost exclusively in the liver
- It is quickly converted into fat (triglycerides) when there is an excess
- It does not activate signalling pathways that indicate satiety
This fundamental difference in metabolism is the basis for the different effects of fructose and glucose on health.
Glycation – the silent ageing process
One of the key mechanisms by which sugars influence ageing processes is glycation – a process in which sugar molecules bind to proteins and lipids without the involvement of enzymes.
What exactly is glycation?
Glycation is a non-enzymatic reaction between reducing sugars (such as glucose and fructose) and amino groups of proteins, lipids and nucleic acids. This process results in the formation of advanced glycation end products (AGEs), which:
- Change the structure and function of proteins
- Damage tissues
- Cause chronic inflammation
- Accelerate the ageing process
- Increase the risk of many diseases
Importantly, fructose is about 10 times more reactive in the glycation process than glucose, making it particularly problematic for health with regular, excessive consumption.
Consequences of glycation for the body
AGEs have a negative impact on many aspects of health:
Skin:
- Damage to collagen and elastin (the main structural proteins of the skin)
- Formation of wrinkles and loss of elasticity
- Deterioration of regenerative capacity
Cardiovascular system:
- Rigidity of blood vessels
- Increased risk of arteriosclerosis
- Disturbed microcirculation
Brain:
- Damage to neurons
- Increased risk of neurodegenerative diseases
- Disturbed cognitive functions
Kidneys:
- Damage to renal glomeruli
- Deterioration of filtration function
- Increased risk of chronic kidney disease
Fructose vs. glucose: effects on key health parameters
Scientific studies show that fructose and glucose have different effects on many health indicators.
Lipid metabolism
Fructose:
- Increases triglyceride synthesis in the liver
- Increases VLDL (very low density lipoprotein) levels
- Promotes the deposition of visceral fat
- Increases the risk of fatty liver
Glucose:
- In normal amounts, it does not significantly increase fat synthesis
- In excess, it can be converted into fat, but this process is less efficient
- It does not have such a direct effect on fatty liver
Appetite regulation
Fructose:
- Does not stimulate insulin or leptin secretion
- Does not inhibit ghrelin (hunger hormone) secretion
- May lead to excessive calorie intake due to lack of satiety signals
Glucose:
- Stimulates insulin and leptin secretion
- Inhibits ghrelin secretion
- Provides a feeling of fullness by activating the corresponding pathways in the brain
Liver metabolism
Fructose:
- Increases oxidative stress in the liver
- Promotes insulin resistance
- Can lead to non-alcoholic fatty liver disease (NAFLD)
Glucose:
- Metabolised in a controlled manner throughout the body
- Less strain on the liver
- Less likely to lead to fatty liver with moderate consumption
Practical tips: how to limit excess fructose?
Knowing about the potentially negative impact of excess fructose on health, it is worth following a few practical strategies:
- Limit products with added glucose-fructose syrup
- Read product labels
- Avoid sweetened drinks
- Choose products without added sugar
- A sensible approach to fruit consumption
- Choose fruit with a lower fructose content (berries, citrus fruits)
- Combine fruit with protein or fat, which slows down the absorption of fructose
- Avoid excessive fruit juice consumption, even 100% juice (lacks fibre)
- Enrich your diet with glycation inhibitors
- Polyphenols (green tea, cocoa, berries)
- Alpha lipoic acid (spinach, broccoli, yeast)
- Carnosine (animal products)
- Vitamin B1 (thiamine)
- Choosing complex carbohydrates
- Whole grain products
- Legumes
- Starchy vegetables
- Regular physical activity
- Improves insulin sensitivity
- Increases glucose utilisation by muscles
- Reduces oxidative stress
Myths and facts about fructose
Myth 1: ‘Fructose is healthy because it comes from fruit.’
Fact: Fructose is found in natural fruit in moderate amounts, together with fibre, vitamins and antioxidants. Industrially added fructose consumed in large quantities is a problem.
Myth 2: ‘Fructose has a low glycaemic index and is therefore suitable for diabetics.’
Fact: Although fructose has a low glycaemic index, an excess of it can increase insulin resistance and contribute to the development of type 2 diabetes by negatively affecting liver metabolism.
Myth 3: ‘Natural sweeteners such as honey or agave are healthier than table sugar’
Fact: Honey and agave syrup contain significant amounts of fructose (agave even up to 90%). From a metabolic perspective, they are not significantly healthier than regular sugar.
Myth 4: ‘Fruit should be eliminated from the diet because it contains fructose.’
Fact: Fruit is a valuable source of vitamins, minerals and antioxidants. The key is moderation and choosing fruit with a lower sugar content.
Conclusion: a balanced approach to carbohydrates
Both fructose and glucose are natural components of our diet. The problem is not their presence, but their excess, especially fructose from industrially processed products.
The key to health is:
- Conscious food choices based on unprocessed foods
- Limiting added sugars, especially glucose-fructose syrup
- Preferring complex carbohydrates over simple ones
- Having an active lifestyle that improves carbohydrate metabolism
Understanding the differences between fructose and glucose and the mechanisms of glycation allows you to make better food choices – choices that support your health and slow down the ageing process instead of accelerating it.
This article is for information purposes only and is not a substitute for professional medical advice. People with chronic illnesses, especially diabetes, should consult a doctor or nutritionist about changes to their diet.