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What are the differences between glucose and fructose?

Do you know the differences between glucose and fructose? Do you know which of the two is better for you? Both are isomers. That is to say that they same chemical structure but their molecular structure is different. Therefore, their metabolic pathways differ and, as a result, the effects they have on the body.


Glucose, like fructose, is a monosaccharide. It has a high glycemic index and is therefore a substance that increases blood glucose as quickly as it is absorbed. This makes it an unhealthy substance for health, as stated in an article published in the magazine Cell Metabolism (English link).

Glucose is the substance most capable of increasing blood glucose. It is found in the form of glucose or starch in many foods (binding of glucose molecules).

However, as a sweetener, it is difficult to find at home in any form other than table sugar. The ordinary consumer can already find it in its pure form in the same form that the food industry has been using for years: dextrose.


Fructose is the sugar with the greatest sweetening power. Paradoxically, its ability to raise blood glucose is much lower than glucose. In fact, the glycemic index has been classified as low.

Unlike glucose, it is easy to find anywhere for home use. It is also the food industry’s favorite sweetener because of its low cost and it has an extremely sweet taste.

Consuming it as a sweetener became popular in the 1960s due to its low cost and the appearance of studies showing the low glycemic index.

In foods we find fructose mainly in fruit. However, the damage we are talking about now cannot be attributed to eating fruit. The density of fructose is very low and the presence of fiber in fruit reduces and slows down the absorption of fructose.

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Cardiometabolic differences between glucose and fructose

The differences between glucose and fructose

The structural differences between glucose and fructose cause their metabolic pathways to differ from each other. Hence, its impact on the body is also different. We will explain this further below.

The body’s energetic fuel

Glucose reaches all cells in the body through specific transporters (especially GLUT2, GLUT3 and GLUT4). This means that all cells use glucose as their main energy fuel.

However, fructose uses GLUT5 transporters and can only form liver glycogen and fatty acids. That is, it is only absorbed by hepatocytes and adipocytes. This results in less likelihood of muscle consumption and a greater tendency to store body fat.

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Fructose, glucose and adiponectin

Adiponectin is a protein

Adiponectin is a protein secreted mainly by adipocytes and cardiomyocytes. The level is inversely related to the percentage of body fat and its production is reduced in obesity and diabetes mellitus. It also plays an important role in the regulation of energy metabolism as this protein:

  • promotes the oxidation of fatty acids.
  • it reduces plasma triglycerides.
  • increases insulin sensitivity.

Metabolic control

The metabolic pathway of fructose is less controlled than that of glucose. For example, fructose does not rely on sodium to enter cells. So all fructose goes from the gut to the liver to be metabolized.

Fructose also cannot be stored in the form of muscle glycogen or used by cells other than adipocytes and hepatocytes. This, along with the ease with which fructose enters the cell, results in rapid activation of lipogenesis (the formation of body fat).

Fructose and fatty acids

Fructose reduces fatty acid oxidation and increases lipid synthesis in the liver. So its overuse is Associated with liver overload and fatty liver disease.

When we take into account that most ultra-processed foods contain it and that in modern society we tend to consume a lot of ultra-processed foods, it’s actually quite clear that achieving over-consumption is quite easy. The excess seems even simpler when we consider that many people choose it as a sweetener because of its lower glycemic index.

The effect of glucose and fructose intake on aortic relaxation

Akther, Alegret, Laguna, Roglans, Roshanak, Sangüesa & Shaligram (2017) studied the effects of glucose and fructose consumption in a population of rats exposed to nitric oxide and found that the aortic artery was less able to relax in rats fed fructose.

This leads to poorer cardiovascular fitness and reduced response to the most commonly used drug therapy (nitroglycerin) in ischemic heart disease (obstruction of blood flow to the heart muscle).

Fructose leads to a worse metabolic and cardiovascular status

Relationship between glucose and fructose and obesity

Based on all of the above, studies show that while glucose consumption increases appetite, fructose is likely the carbohydrate with the highest obesogenic capacity. Its consumption has been associated with it metabolic syndrome.

Fructose consumption has also been associated with problems such as insulin resistance, a poor lipid profile and an inadequate cardiovascular response.

Practical Considerations About Glucose and Fructose

We already know the differences between glucose and fructose and their impact on health, but what does this information mean in our daily life? We will answer a number of questions about this.

What do I do with fructose?

As we have already seen, despite the low glycemic index consumption of fructose means than glucose, an endless number of negative effects which can lead to more obesity, diabetes, liver disease and everything else these problems entail.

In this sense, we have to keep in mind that most ultra-processed foods contain fructose. So now you have one more reason to stop consuming ultra-processed foods!

When do you consume glucose?

One of the main differences between glucose and fructose is the ability to increase blood glucose. Therefore, we should choose to consume glucose only when we need a quick energy boost. This is, for example, during intensive physical exercise or at the end of it.

If the energy requirement is very high (intense physical activity> than 2.5-3 hours), we recommend to choose combined carbohydrates with a high glycemic index. This can be honey, table sugar or the simultaneous use of glucose and fructose. In this way you saturate all transporters that transport the sugar to the cells and thus meet the energy demand.

Doctors don’t recommend glucose and fructose

In all other circumstances, however, we must try to avoid glucose. At the same time, we should not opt ​​for fructose either, because, despite its low glycemic index, it has a very negative cardiometabolic impact.

Neither glucose and fructose nor heat-modifiable sweeteners are good alternatives for overweight, obese or diabetes mellitus people. Nor is the use of heat-affected sweeteners a good alternative.