The glycaemic index (GI) ranks carbohydrate foods by how quickly they raise blood glucose compared with pure glucose (GI 100).

Low, medium and high

• Low GI (55 or less): lentils, chickpeas, most beans, oats, most fruit, milk and yoghurt, wholegrain pasta.
• Medium GI (56–69): basmati rice, wholemeal bread, sweetcorn.
• High GI (70+): white bread, cornflakes, rice cakes, baked potatoes, sugary drinks.

The limits of GI

• It measures foods eaten alone; adding protein, fat or fibre to a meal lowers the overall response.
• Low GI doesn't mean healthy: chocolate and crisps can be low GI because of their fat content.
• Cooking, ripeness and processing change GI.

Glycaemic load

Glycaemic load (GL) adjusts for portion size: GL = GI × grams of carbohydrate in a portion ÷ 100. Watermelon has a high GI but a low GL because a typical portion contains little carbohydrate.

Does it matter?

For general health, focusing on fibre-rich, minimally processed carbohydrates naturally lowers the GI of your diet. For people managing diabetes, GI can be one useful tool among many — ideally discussed with a dietitian.