The glycemic index ranks carbohydrate foods by how fast they raise blood glucose, on a scale where pure glucose scores 100. The standard bands: low is 55 or below, medium is 56–69, and high is 70 and above. White bread scores around 75, spaghetti around 49, lentils around 32 — same macronutrient, wildly different speeds.
For someone on insulin, GI is essentially a preview of your curve shape. A high-GI food races your insulin's onset and often wins, producing the spike-then-drop pattern; a low-GI food climbs slowly and can outlast a fast insulin's action. Neither is automatically good or bad — a fast carb is exactly what you want when treating a low.
GI has real limits, though:
- It ignores portion size — that is what glycemic load fixes.
- It is measured on foods eaten alone; add fat or protein and the real-world number shifts.
- Ripeness, cooking method, and processing move it a lot (baked vs boiled sweet potato nearly doubles).
- Individual responses vary — two people can eat the same food and see different curves.
Use GI as a rough speed rating, not gospel. Your CGM after a real meal is the ground truth for how a food behaves in your body.
