Glycemic index explained: low, medium and high
The glycemic index (GI) ranks carbohydrate foods from 0 to 100 by how quickly they raise blood glucose compared with pure glucose. A GI of 55 or less is low, 56 to 69 is medium and 70 or more is high. GI does not account for portion size, so the amount you eat still matters.
What does the glycemic index measure?
The glycemic index compares how fast the carbohydrate in a food raises blood glucose with the same amount of pure glucose, which scores 100. Foods that raise glucose slowly score lower.
| Category | GI value |
|---|---|
| Low | 55 or less |
| Medium | 56 to 69 |
| High | 70 or more |
Why is GI not the whole story?
- Portion size. A large portion of a low-GI food still contains a lot of carbohydrate.
- The rest of the meal. Protein, fat and fibre eaten together can slow how fast glucose rises.
- How the food is prepared. Ripeness, cooking and processing change the GI.
- You. People respond differently to the same food.
How can I use it?
Treat GI as one tool among several, alongside portion size and balanced meals such as the plate method. The best test is your own record. Note what you ate and your readings afterwards, as described in what to write in a blood sugar diary.
Information, not medical advice. Talk to your care team about your own targets and treatment. Never use a converter or a diary entry to work out an insulin or medicine dose.
Sources
Frequently asked questions
Is a low-GI food always a better choice?
Not always. GI says nothing about portion size, fat, salt or overall nutrition. A low-GI food can still be a poor choice in a large portion.
Does cooking change the GI?
Often, yes. Ripeness, cooking time, processing and what you eat with the food can all change how quickly it raises glucose.
Where can I look up the GI of a food?
The University of Sydney runs an international GI database at glycemicindex.com. A dietitian can also help.
Keep reading
The plate method
How to build a balanced plate with the plate method: half non-starchy vegetables, a quarter protein and a quarter high-fibre carbohydrate.
Food and carbsReading labels for carbs
How to find carbohydrates on a nutrition label: serving size, total carbohydrate, fibre and added sugars, with a simple way to work out your portion.
Daily habits and self-careBlood sugar diary
A practical guide to keeping a blood sugar diary: what to record, why context matters, and a simple template you can copy.