Carbohydrates are essential components of our diet, providing energy for our body. However, different types of carbohydrates affect blood sugar and metabolism differently, which is a particularly important consideration when dieting. In this article we will review simple and complex carbohydrates and how they are digested and absorbed.

The different types of carbohydrates

Simple carbohydrates

Simple carbohydrates are rapidly digestible sugars that quickly raise blood sugar levels. There are two main types:

• Monosaccharides: these are the basic sugar molecules, such as glucose, fructose and galactose.
• Disaccharides: they consist of two monosaccharides, such as sucrose (table sugar), lactose (milk sugar) and maltose (maltose).

Complex carbohydrates

Complex carbohydrates are made up of longer-chain sugar molecules and are digested more slowly, so they provide more stable blood sugar levels. There are two main categories:

• Oligosaccharides: short-chain sugars such as maltodextrin, raffinose and stachyose. Most of these are resistant to digestive enzymes, so they pass undigested into the large intestine, where they act as selective nutrients for bacteria that are beneficial to the body.
• Polysaccharides: long-chain sugars such as starch and cellulose. Starch is an important source of energy, while cellulose is mainly found in plant fibres and does not break down during digestion.

The effect of carbohydrates on blood glucose levels

Simple carbohydrates are quickly absorbed into the bloodstream, causing a rapid rise in blood sugar levels. This provides a short-term energy boost, but is quickly followed by a drop in blood sugar levels, which can cause fatigue and hunger.

In contrast, complex carbohydrates are digested more slowly, releasing glucose gradually into the bloodstream, providing longer-lasting energy and resulting in more stable blood glucose levels.

Digestion and absorption of carbohydrates

Digestion

Digestion of carbohydrates starts in the mouth, where the enzyme amylase in saliva breaks down starch into maltose. In the stomach, the acidic medium inactivates amylase, so carbohydrate digestion continues mainly in the small intestine. Here amylase released by the pancreas continues the breakdown of starch into maltose and other disaccharides.

Absorption

The epithelial cells of the small intestine use enzymes to break down disaccharides into monosaccharides such as glucose, fructose and galactose, which are then absorbed into the bloodstream. Glucose can be used immediately as an energy source or stored as glycogen in the liver and muscles.

Dieters’ considerations

When dieting, the type and amount of carbohydrates is important. Simple carbohydrates can cause rapid fluctuations in blood glucose levels, making weight loss and blood glucose control more difficult. Complex carbohydrates, on the other hand, can help to keep energy levels more stable and reduce hunger.
Adequate carbohydrate intake is important and depends on the individual’s lifestyle, health and goals. Low glycaemic index (GI) foods, such as fibre-rich grains, vegetables and pulses, provide longer-lasting satiety and steady blood sugar levels.

Summary

Carbohydrates are an essential source of energy, but their types and effects on the body vary considerably. Simple carbohydrates provide quick energy, while complex carbohydrates provide longer-term, stable energy. When dieting, it makes sense to give preference to complex carbohydrates to avoid blood sugar fluctuations and ensure adequate energy supply.