Functions of carbohydrates in our body

Carbohydrates are an essential part of our diet. Most importantly, they provide the energy for the most obvious functions of our body, such as moving or thinking, but also for the ‘background’ functions that most of the time we do not even notice1. During digestion, carbohydrates that consist of more than one sugar get broken down into their monosaccharides by digestive enzymes, and then get directly absorbed causing a glycaemic response (see below). The body uses glucose directly as energy source in muscle, brain and other cells. Some of the carbohydrates cannot be broken down and they get either fermented by our gut bacteria or they transit through the gut without being changed. Interestingly, carbohydrates also play an important role in the structure and function of our cells, tissues and organs.

Types of carbohydrates

Monosaccharides, disaccharides and polyols

Simple carbohydrates – those with one or two sugar units – are also simply known as sugars. Examples are:

Glucose and fructose: monosaccharides that can be found in fruits, vegetables, honey, but also in food products like glucose-fructose syrups

Table sugar or sucrose is a disaccharide of glucose and fructose, and occurs naturally in sugar beet, sugar cane and fruits

Lactose, a disaccharide consisting of glucose and galactose, is the main carbohydrate in milk and dairy products

Maltose is a glucose disaccharide found in malt and starch derived syrups

Monosaccharide and disaccharide sugars tend to be added to foods by manufacturers, cooks and consumers and are referred to as ‘added sugars’. They may also occur as ‘free sugars’ that are naturally in honey and fruit juices.

Polyols, or so-called sugar alcohols, are also sweet and can be used in foods in a similar way to sugars, but have a lower calorie content compared to normal table sugar (see below). They do occur naturally, but most polyols that we use are made by the transformation of sugars. Sorbitol is the most commonly used polyol in foods and drinks, while xylitol is frequently used in chewing gums and mints. Isomalt is a polyol produced from sucrose, often used in confectionery. Polyols can have a laxative effect when eaten in too large quantities.

What are carbohydrates?

At their most basic, carbohydrates are made of building blocks of sugars, and can be classified according to how many sugar units are combined in their molecule. Glucose, fructose and galactose are examples of single-unit sugars, also known as monosaccharides. Double-unit sugars are called disaccharides, among which sucrose (table sugar) and lactose (milk sugar) are most widely known. Monosaccharides and disaccharides are usually referred to as simple carbohydrates. Long-chain molecules, such as starches and dietary fibres, are known as complex carbohydrates. In reality, though, there are more distinct differences. Table 1 gives an overview of the major types of carbohydrates in our diet.

Carbohydrates are also known under the following names, which usually refer to specific groups of carbohydrates1:

sugars

simple and complex carbohydrates

resistant starch

dietary fibres

prebiotics

intrinsic and added sugars

The different names come from the fact that carbohydrates are classified depending on their chemical structure, but also based on their role, or source in our diet. Even leading public health authorities have no aligned common definitions for different groups of carbohydrates.