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What is sugar?

In the next few blogs we will tackle the topic of “sugar”. There are some daunting headlines in the media: Sugar is a silent killer. Sugar causes obesity and diabetes. Sugar causes cancer. Sugar seems to be the cause of all evil. We are constantly bombarded with these scary messages. We also hear that sugar is an important fuel for athletes and that athletes need to take gels and drinks that contain sugars. Is it possible that there is some truth in both of these messages? What to believe? In a series of blogs we will tackle this topic. In this first blog we will discuss what “sugar” is…

Infographic on what is sugar

What exactly is sugar?

Sugar is a carbohydrate. The name carbohydrate indicates molecules built of carbon (carbo) and hydrogen (hydrate; water). It also contains oxygen. The general formula of carbohydrate is CH2O. In other words, the molar ratio of carbon, hydrogen, and oxygen is 1:2:1 in all carbohydrates. The most common carbohydrate in the body is glucose. C6-H12-O6. Glucose is formed during photosynthesis, and we obtain almost all our carbohydrates from plants. Carbohydrates, however, can be found in all living cells. Glucose is a good fuel for the muscle and it is stored as glycogen. Glycogen is a starch: a long chain of glucose molecules.

The sugars in our diet

Glucose is a small molecule, a monosaccharide, also called grape sugar. If we link two glucose molecules, malt sugar or maltose is formed. Fructose is another monosaccharide that we will discuss in more detail in a separate blog. If we combine glucose and fructose we get sucrose and this is the most common form of sugar in our diet: table sugar. There is another monosaccharide and that is galactose. Galactose combined with glucose gives lactose, the sugar we find in milk. These mono and disaccharides are all sugars. They have varying levels of sweetness with fructose being a clear winner of the sweetness competition. All these mono and disaccharides, so glucose, fructose galactose, sucrose, lactose and maltose are all sugars present in our diet (as we discussed in a previous blog).

Infographic simple and complex carbohydrate

Complex carbohydrates

At the other end of the spectrum we have complex carbohydrates. Complex carbohydrates are technically a combination of glucose molecules… a chain of glucose molecules. The chain can be short 6-20 glucose molecules (we call them maltodextrins, something we find in many sports nutrition products) or extremely long chains, we call that starch. These longer chains are usually less sweet than the sugars.

What you need to know about sugar

There are a few things that are important to understand about sugar and polysaccharides (multiple glucose units).

  • Sugars are generally sweet, polysaccharides like maltodextrins or starch less so.

  • Fructose is the sweetest carbohydrate. 1.5 times sweeter than sucrose. Galactose is half as sweet as sucrose. The sweetness does not say anything about function.

  • In the ripening process of foods, complex carbohydrates are broken down to sugars and therefore fruits will taste sweeter.

  • The cracker experiment: A cracker contains a lot of starch and does not have a lot of taste and it is not sweet. However, if you keep a cracker for longer in your mouth, amylase in saliva will start to break down the starch, forming sugar. So, if you keep the cracker in your mouth long enough, it will become sweet. Try it!

  • Not all sugars are fast! Some sugars are fast, some are slow.

  • Maltodextrins and some starches (amylopectin) behave almost identical to glucose after ingestion.

  • The terminology 'complex' and 'simple' carbohydrates is used in different ways, and this is the source of a lot of confusion.

Infographic sugar and complex carbohydrate

What are the misconceptions about sugar

There is a lot of confusion and many misconceptions about sugar.

  • One common misconception is that we refer to sugars as fast and starches as slow. This is an important misunderstanding. Some sugars are fast, some sugars are slow, some starches are indeed slow but many are just as fast as glucose…

  • With slow or fast we mean how rapidly they appear as glucose in the blood. Maltodextrins and some starches behave identical to glucose. They are so quickly broken down to glucose that the end-result, when you measure in the blood, is the same.

  • To add to the confusion, the term complex carbohydrate is also used in a different way. It is used to indicate for foods that contain starches but also other nutrients and fibre. For example, whole grains and brown rice are often referred to as complex carbohydrates. But we should probably refer to these carbohydrates as “unrefined” and not as “complex” carbohydrates. Unrefined carbohydrates are an important part of a healthy diet, sugars are not. For athletes refined carbohydrates may be preferred in some situations over unrefined carbohydrates.

In the next blog, we discuss the role of sugar in providing energy.


  1. Jeukendrup AE and Gleeson M. Sport Nutrition 2018 Human Kinetics Champaign IL


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