Dr Aidin Rawshani

Sugar, fructose (fructose), glucose (glucose): risks, benefits, weight, diabetes


What is the difference between fructose (fruit sugar) and glucose (glucose) and how does sugar affect my health?

For several decades, scientists, doctors and government agencies were convinced that fatty foods gained weight, gained type 2 diabetes, high blood lipids and coronary heart disease. This made people eat less and less fat and instead eat more carbohydrates of all kinds, including sugar and starch.

It was only in the early 2000s that scientists understood that it was really sugar and fast carbohydrates that were harmful. Unfortunately, in Sweden and the other ‘modern countries’, carbohydrate-rich food has dominated for several decades. It was nothing unusual for sugar and starch to account for up to 20% of the energy intake in one day.

The American Heart Association is an organization whose researchers characterised the whole world’s dietary habits, including the Swedes. At the beginning of the 21st century, they issued guidelines proposing reducing the intake of sugar. It was suggested that men should eat a maximum of 150 kcal from sugar daily, and the corresponding figure for women was 100 kcal. 7

Read more about How fat and fatty foods affect health, blood lipids and mortality.

It is most likely that the huge increase in diabetes, overweight and obesity in the world is explained by two things:

  • Physical inactivity — we move far too little
  • Unhealthy food — especially a high intake of sugar and other fast carbohydrates. Also, excess calorie is an important factor.

It should already be mentioned that exercise (physical activity) is certainly very healthy, but physical activity is not very effective for those who want to lose weight.

Before we go further: what is sugar, glucose, fructose and carbohydrates?

Glucose (glucose), fructose (fruit sugar), lactose (milk sugar), table sugar (powdered sugar), starch and fiber are all different types of carbohydrates. All carbohydrates are made up of monosaccharides. There are three different monosaccharides and they are as follows:

  • Glucose — Glucose is also called glucose. When you talk about blood sugar, you really mean glucose in the blood.
  • Fructose — Fructose is also called fruit sugar. Sweet fruits contain a lot of fructose. Today, fructose is also used as an additive in beverage and food.
  • Galactose

These three monosaccharides build up more complex carbohydrates. For example, starch consists of long chains of glucose (which is interconnected).

  • Sugar powder (table sugar): consists of fructose and glucose that are interconnected (the units are called sucrose).
  • Potatoes, rice and pasta: contain large amounts of starch consisting solely of glucose.
  • Vegetables: usually contain a lot of fiber, which also consist of glucose units interconnected.

The human intestines can break down all carbohydrates into monosaccharides that are subsequently absorbed. However, the human body wants to use glucose only as an energy source and therefore it has enzymes that can convert fructose and galactose into glucose. This means that no matter what carbohydrates then eat, the body can eventually extract glucose. The only exception is fiber: the human body can not break down fibers, which, therefore, pass through the intestine and out through the stool.

What is sugar? When we talk about sugar, we usually mean some kind of glucose and/or fructose. Most “sugar products” contain both fructose and glucose.

Is sugar dangerous?

any people are wondering whether sugar and carbohydrates are harmful. The supplementary question is whether all sugars/ carbohydrates are harmful. First, let’s note that sugar is not a poison. From a biochemical perspective, man can eat sugar and the body can handle it perfectly well. The problem is that far too many people eat sugar in quantities that the body cannot cope, and then sugar is directly harmful.

So sugar as a chemical substance is not toxic, but in the quantities we are accustomed to eating sugar, it is directly harmful. The same principle applies to most substances in the body. Another close example is LDL cholesterol, which is also called “bad cholesterol”. LDL cholesterol is vital to us humans. Normally, LDL cholesterol usually ranges from 2 mmol/L to 5 mmol/L.Within the range of 2 to 5 mmol/L, LDL is not harmful.

But what if you double your LDL to 10 mmol/L? Well, then, most likely, you get an acute heart attack sooner or later. Just the same principle applies to a wide range of natural substances in the body. Sugar applies roughly the same principle: it is harmless in small amounts but when it gets too much it becomes harmful.

Unfortunately, we do not manage to eat small quantities, but too often we eat far too much. Therefore, for the vast majority of people, sugar poses a health risk. Note that man does not need sugar; we can get all the carbohydrates we need (which is usually not very much) without eating sugar.

Fructose or glucose: what is the worst?

From a chemical point of view, fructose and glucose are very similar. However, fructose is more than twice as sweet as glucose. Common sweeteners and additives usually consist of a mixture of fructose and glucose. For example, table sugar (powdered sugar) consists of fructose and glucose that are interconnected (the units are then called sucrose, or sucrose).

Pure glucose is not very sweet, at least not compared to fructose and this is the reason why food manufacturers tend to use additives containing both fructose and glucose.

The body’s handling of glucose and fructose differs significantly. All cells in the body can use glucose as an energy source. Glucose is actually the most used energy source on the planet. Both animals and plants prefer to burn glucose. Fructose, however, cannot be used as an energy source directly; it must be converted into other substances which can then be used as an energy source (the liver can convert fructose into glucose). This means that glucose is more efficient as an energy source (since glucose does not need to be converted or processed before it can be used as a fuel).

When glucose gets into the blood, it stimulates the pancreas (pancreas) to release insulin. This has several effects in the body:

  1. Insulin signals to the body’s cells to absorb glucose from the blood.
  2. Insulin signals to the fat tissue to stop breaking down fat and instead use glucose to make more fat.
  3. Insulin signals to the liver to stop producing glucose and instead absorb and store glucose. In the liver, glucose is stored in a form called “glycogen”.

Thus, glucose leads to the release of insulin, which in turn leads to reduced fat breakdown and increased production of fat. Many scientists actually believe that insulin is the reason why we gain weight.

Fructose differs in all these respects. Fructose does not stimulate the pancreas and therefore does not lead to the release of insulin. Most cells in the body can not take up fructose, but the liver can do it. The liver is able to convert fructose according to the healing:

  1. Fructose can be converted into glucose.
  2. Fructose can be converted into lactate, which in turn can be used in several ways.
  3. Fructose can be converted into fat (fatty acids).

Unfortunately, the liver is not able to regulate the metabolism of fructose as accurately as glucose. Most of all fructose that enters the liver will be transformed as described above. Therefore, if you eat a lot of glucose, too much fatty acids can be formed. In the liver, this can lead to fat accumulation and therefore both fatty liver and insulin resistance in the liver (insulin resistance is the cause of type 2 diabetes). The fat can also be sent out into the body, increasing the concentration of fatty acids in the blood, which in turn can lead to insulin resistance in the body as well as more fat around the organs and under the skin.

Fructose can also lead to a shift in the liver’s metabolism towards an “inflammatory state” and increase the lifes’ production of uric acid (urate). This is believed to worsen both high blood pressure and the ability of blood vessels to regulate blood pressure and prevent the formation of blood clots.

Some studies have shown that large amounts of fructose can cause metabolic disorders; compared to glucose, fructose was inferior to insulin resistance, blood lipids, blood pressure and weight among people with overweight. However, other studies show that there was no difference between fructose and glucose in these respects.

There are even studies that show that replacing part of the glucose with fructose can be healthy. 8

Fructose and glycaemic index (GI)

Glucose and all starches have a high glycemic index, which means that they give sharp increases in blood sugar and insulin when eating them. Fructose actually has a very low glycemic index. Since a high glycemic index is considered unhealthy, fructose is likely to be better than glucose from a health perspective. 9 In other words, fructose is probably no more harmful than glucose.

Is starch healthier than fast carbohydrates (sugar)?

Yes, sir. Starch consists of glucose. Studies looking at the difference between eating pure sugar and eating starch show that starch is just as bad in body weight, glucose tolerance, insulin levels, cholesterol, triglycerides and fatty acids. The only difference is that pure sugar can give a little higher blood sugar than starch, otherwise they are just as bad. 10

Don’t focus on calories — focus on quality

Fruits contain large amounts of fructose. A good rule of thumb is that a fruit containing 80 kcal contains about 10 g of fructose. If fructose were harmful in high doses, people who eat a lot of fruit should show signs of ill health. The fact is that basically all studies on fruit and health show that people who eat a lot of fruit are healthier, live longer and they are slimmer!

In addition, diabetes is less common among those who eat a lot of fruit. 11

There are even randomised clinical trials where very high doses of fruit were given to participants (up to 200 g of fructose per day). This study showed that there were no adverse effects of eating a lot of fruit (regarding body weight, blood pressure, insulin, blood lipids). On the contrary, there were signs that those who ate so much fruit got better values. 12

So why is fructose as an additive to food and drink harmful but not fructose in fruit? The answer is simple: fructose in whole fruits does not give the same acute load on the liver. When we drink sweetened soft drinks and foods, the concentration of fructose rises rapidly in the liver and the liver cannot take care of all fructose.

Whole fruits, however, can not be absorbed as quickly. In fruit there is a portion of fiber (which complicates the absorption of sugar in the fruit). Furthermore, the fruit itself must be processed in the stomach and intestines before the sugar can be absorbed. Last but not least, fruit also contains other nutrients (vitamins, minerals, etc.) and antioxidants that can possibly protect the liver from inflammation.


  1. Fructose in whole fruits is not harmful. On the contrary, science suggests that fruit is healthy.
  2. Sugar and fast carbohydrates are one of our biggest public health problems. It pushes the development of excess weight, obesity, diabetes, cardiovascular disease and some forms of cancer.
  3. Sugar and fast carbohydrates have no nutritional value for man. There are options that are significantly better.
  4. Drink and food purchased in Swedish stores and restaurants, as a rule, have unnecessary and unhealthy additives of sugar, in the form of glucose and fructose. That type of carbohydrates is definitely harmful and there does not seem to be much difference between glucose and fructose when used as an additive in food.
  5. Sugar and starch are about as unhealthy.

Main source: Examining the Health Effects of Fructose David S. Ludwig, JAMA. 2013;310(1):33-34.

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