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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 is better for you?

Both are isomers, that is, they have the same chemical formula, but their molecular structure is different. Therefore, their metabolic pathways differ, and, as a consequence, so do their effects on the body.

Glucose

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

Glucose is the substance most capable of raising blood glucose.

It’s found in many foods in the form of glucose or starch (binding of glucose molecules). However, as a home sweetener, it’s difficult to find in a form other than table sugar.

Despite the difficulties, the ordinary consumer can already find it in its pure form in the same format that the food industry has been using for years: dextrose.

Fructose

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

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

Consuming it as a sweetener became popular in 1960 as a consequence of its low cost together with the appearance of researches showing its low glycemic index.

In natural foods, we find it mainly in fruit. However, the damages that we’re about to talk about aren’t attributable to simply eating fruit. This is because the density of fructose is very low and that its richness in fiber reduces and delays its absorption.

Cardiometabolic differences between glucose and fructose

The structural differences between glucose and fructose cause their metabolic pathways to differ from each other and therefore their impact on the body is also different.

The body’s energy fuel

Glucose reaches all cells in the body through specific transporters (notably, 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’s only absorbed by hepatocytes and adipocytes. This results in less opportunity for use and a greater tendency to accumulate body fat.

Fructose, glucose, and adiponectin

Adiponectin is a protein secreted mainly by adipocytes and cardiomyocytes. Its level is inversely proportional to the percentage of body fat and is reduced in states of obesity and diabetes mellitus.

Also, it has an important role in the regulation of energy metabolism as it:

  • Favors the oxidation of fatty acids
  • Reduces plasma triglycerides
  • Increases sensitivity to insulin

In this regard, everyone knows that glucose has more capacity than fructose to induce the release of adiponectin and achieve the benefits associated with the increase of it.

Metabolic Control

The metabolic pathway of fructose is less controlled than that of glucose. For example, fructose doesn’t depend on sodium to enter cells. Thus, all fructose travels from the intestine to the liver for metabolism.

Also, fructose cannot be accumulated in the form of muscle glycogen or used by cells other than adipocytes and hepatocytes. This, along with its ease of entry into the cellular interior, results in rapid activation of lipogenesis (formation of body fat).

Fatty acids

Fructose reduces fatty acid oxidation and increases lipid synthesis in the liver. Thus, its excessive consumption has been linked to liver overload and fatty liver.

If we take into account that most processed foods contain it and that in modern society we tend to eat lots of processed foods, it’s actually evident that reaching excess consumption is quite easy. The excess seems even simpler if we think that many people have chosen it as a sweetener because of its lower glycemic index.

The effect of glucose and fructose intake on aortic artery relaxation

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

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

Fructose leads to a poorer metabolic and cardiovascular state

Based on all of the above, even though glucose consumption increases appetite, studies find that fructose is probably the carbohydrate with the highest obesogenic capacity. In fact, its consumption has been related to the already famous “metabolic syndrome“.

Also, fructose consumption has been linked to insulin resistance, poorer lipid profile, and inadequate cardiovascular response.

Practical considerations based on glucose and fructose differences

We already know the differences between glucose and fructose and their impact on health, but what does this information mean daily?

What do I do with fructose?

As we have already seen, despite its low glycemic index, its consumption supposes an endless number of negative effects that end up in more obesity, diabetes, hepatic conditions, and everything that these carry with them.

In this sense, we must take into account that most processed foods contain fructose in their ingredients. So now you have one more reason to stop consuming processed foods!

When to consume glucose?

One of the main differences between glucose and fructose is its ability to raise blood glucose. Therefore, we should choose to consume glucose when we need a quick energy boost. This would be during the practice of intense physical exercise or at the end of it.

If the energy demand is very high (intense physical activity >2.5-3 hours), we recommend choosing combined carbohydrates with a high glycemic index.

This could be honey, table sugar, or the concomitant use of free glucose and fructose. This way, you’re saturating all the transporters that carry the sugar into the cells and thus satisfying the energy demand.

A low glycemic index alternative

However, in any other circumstances, we should try to avoid glucose. At the same time, we shouldn’t opt for fructose either since, despite its low glycemic index, it has a very negative cardiometabolic impact. Nor is the use of heat-affected sweeteners a good alternative.

Neither glucose, fructose nor heat sweeteners are good alternatives for people who are overweight, obese or have diabetes mellitus.

Doctor’s don’t recommend glucose or fructose

If we’re not practicing intense physical exercise, glucose with a low glycemic index is ideal. However, unfortunately, it doesn’t exist. Therefore, the best alternative is coconut sugar.

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