Glycaemic index (GI)

The glycaemic index (GI) measures how much 50 grams of carbohydrate from a food raises your blood sugar – compared with glucose, which is given a value of 100. The concept was developed in 1981 by the Canadian nutrition researcher David Jenkins. Values up to 55 are considered low, 56 to 69 medium and 70 or above high. White bread comes in at around 75, cornflakes at about 80, coarse wholegrain rye bread at 50 to 60 (finely milled wholemeal wheat bread, by contrast, is barely lower than white bread), lentils at about 30 and most vegetables far below that.

Why does this matter? Foods with a high GI make your blood sugar rise rapidly, your body releases a lot of insulin, and afterwards your blood sugar often drops below where it started – a classic trigger for cravings. Low-GI foods release their energy more steadily and keep you full for longer.

But the GI has its pitfalls. It refers to 50 grams of carbohydrate, not to a portion: watermelon has a high GI (around 75) but contains so little carbohydrate that a normal portion barely affects your blood sugar. That's why there's also the glycaemic load (GL), which factors the actual amount of carbohydrate into the GI: GL = GI × grams of carbohydrate per portion ÷ 100. On top of that, preparation, ripeness, and any fat, protein and fibre in the same meal change the value considerably – and the response varies from person to person.

For everyday life, this rule of thumb is enough: keep food as unprocessed as possible, choose wholegrain over white flour, combine carbohydrates with protein and vegetables, and cook pasta “al dente”. If you have diabetes, you can work with GI and GL in a targeted way – ideally together with your doctor or a dietitian. Healthy children don't need tables.