Glycaemic Index (GI) ranks foods from 0–100 based on how fast 50 g of their carbohydrate raises blood glucose compared to pure glucose. Low GI (≤55), medium (56–69), high (≥70). Glycaemic Load (GL) multiplies GI by the grams of carbohydrate in a typical serving — it’s more practically useful because it accounts for how much you actually eat.
A few caveats: GI is measured in fasting individuals eating a food in isolation. Mixing foods, cooking method, ripeness, and individual variation all change real-world glucose responses substantially.
Higher-GI diets are associated with modestly increased risk of type 2 diabetes and cardiovascular disease in observational studies, though causality is debated. Practically, choosing wholegrains over refined grains, legumes, and minimally processed foods achieves a lower dietary GI — and delivers fibre and micronutrients — without needing to memorise GI tables.