Carbohydrates are an important source of energy for your body, but not all carbs affect you in the same way. The glycaemic index (GI) indicates how quickly a carbohydrate-containing food raises your blood sugar — which is exactly why making the right choices during your eating window can make a difference when practising intermittent fasting. Below, you'll discover the 3 types of carbohydrates, how the glycaemic index works and which foods are best to choose.
In this article:
- What are carbohydrates?
- The 3 types of carbohydrates
- Glycaemic index
- GI values of commonly eaten foods
- Carbohydrates during your eating window
- Frequently asked questions
What are carbohydrates?
You often hear that "carbs are the enemy if you want to lose weight." That's not quite true — it's not just about how many carbohydrates you eat, but also which ones you choose.
Carbohydrates is the collective term for sugars, starches and fibre. Digestible carbohydrates are broken down into glucose in the body. One of their main functions is to provide energy: 1 gram of carbohydrate provides around 4 kcal. Your body can store carbohydrates as glycogen, mainly in the liver and muscles. When these stores are sufficiently full and you consistently consume more energy than you use, excess energy can be stored as fat.
The 3 types of carbohydrates
- Monosaccharides are the simplest sugar molecules. Examples include glucose, fructose (fruit sugar) and galactose (a component of lactose).
- Disaccharides consist of two monosaccharides. Examples include sucrose (fructose + glucose), lactose (glucose + galactose) and maltose (2 x glucose).
- Polysaccharides are large molecules made up of many monosaccharides. Examples include starch (found in plants), glycogen (stored in muscles and the liver) and cellulose (a plant fibre).
As a general rule, simple or rapidly available sugars are found in foods such as sweets, soft drinks and many highly processed products. Fruit and honey also naturally contain simple sugars. Complex carbohydrates are found in foods such as pulses, potatoes and wholegrain products, which often provide fibre and other valuable nutrients as well.
Glycaemic index
The glycaemic index indicates how quickly and how much a carbohydrate-containing food raises blood sugar compared with glucose. Foods with a low GI are generally digested more slowly or cause a slower rise in blood sugar than foods with a high GI. As a general guide, a GI below 55 is considered low, between 55 and 70 is considered medium, and above 70 is considered high.
Tip: If you're trying to lose weight or want to avoid large fluctuations in blood sugar, foods with a lower glycaemic index can be a useful choice. Keep in mind that portion size, preparation method and combining carbohydrates with protein, fat and fibre can also affect your blood sugar response.
GI values of commonly eaten foods
| Carbohydrates per 100 g | Glycaemic Index | |
| Potato gratin | 11.3 g | 70 |
| Potato with skin | 19.0 g | 60 |
| Basmati rice | 28.8 g | 58 |
| Ripe banana | 20.0 g | 51 |
| Cornflakes | 23.0 g | 81 |
| Cooked wholewheat pasta | 15.8 g | 50 |
| Cooked white pasta | 23.8 g | 55 |
| Glucose | 100 g | 100 |
| Cooked quinoa | 18.0 g | 53 |
| Wholemeal bread | 49.4 g | 55 |
| Wholewheat macaroni | 26.5 g | 47 |
Carbohydrates during your eating window
With intermittent fasting, you eat within a limited window of the day. That's why it makes sense to pay attention to the quality of the carbohydrates you choose during your eating window. Foods with a lower glycaemic index and a good amount of fibre can contribute to a steadier supply of energy. Combine them with enough protein, vegetables and healthy fats to create balanced, satisfying meals.
Written by Claudia — Industrial Engineer in Biochemistry, weight-loss consultant and certified Intermittent Fasting Specialist. With 25 years of experience in nutrition and metabolism, she has also personally followed a 16:8 intermittent fasting routine for many years. Learn more about Claudia
