What the glycemic index measures
The glycemic index (GI) ranks carbohydrate foods from 0 to 100 by how much they raise blood glucose in the two hours after eating, compared with a reference food, either pure glucose or white bread. The method was introduced in 1981 by David Jenkins and colleagues, who fed volunteers portions containing 50 g of available carbohydrate and compared the blood sugar curves. Available carbohydrate means total carbohydrate minus fiber.
Foods are usually grouped into three bands.
| Band | GI | Typical examples (approximate) |
|---|---|---|
| Low | 55 or less | Lentils, chickpeas, kidney beans, pearl barley, apples, strawberries, plain yogurt |
| Medium | 56 to 69 | Rolled oats, pineapple, some brown rice, sweet corn |
| High | 70 or more | White bread, white rice, cornflakes, baked potato, watermelon |
Values differ between studies because of variety, ripeness, cooking time and the people tested, so read them as ranges. The International Tables of Glycemic Index and Glycemic Load Values, most recently updated in 2021, and the University of Sydney GI database are the standard sources.
Why glycemic load is more useful
GI is measured on a fixed 50 g of carbohydrate, which is not how people eat. You would need to eat about a kilogram of carrots to reach 50 g of carbohydrate, but only a small portion of rice. Glycemic load (GL) fixes that by combining the quality of the carbohydrate with the quantity in a real serving.
GL = GI x grams of available carbohydrate in the serving / 100
A GL of 10 or below is low, 11 to 19 is medium and 20 or above is high, per serving.
A worked example
Take 150 g of cooked white rice. It holds roughly 42 g of available carbohydrate and has a GI near 73, so its GL is about 31, which is high. Now take 150 g of cooked lentils. They hold roughly 18 g of available carbohydrate and have a GI near 30, so the GL is about 5. The lentils deliver a similar amount of food with a fraction of the blood sugar effect, and they bring about 12 g of fiber and a lot of protein as well. The numbers are approximate, but the gap is real.
Watermelon shows the opposite problem. Its GI is high, around 76, yet a normal slice has little carbohydrate, so the GL is only about 8. This is why GL is the better guide for portions and GI is the better guide for choosing between similar foods.
What changes a food's glycemic response
- Processing. Finely milled flour is digested far faster than the intact grain. Wheat flour, including whole wheat flour, raises blood sugar quickly, which is why these recipes use legumes, nuts and seeds instead.
- Fiber and viscosity. Soluble fiber such as beta-glucan in barley and the gel formed by psyllium and chia slows absorption.
- Ripeness. A ripe banana has more rapidly digested sugar than a green one.
- Cooking. Pasta cooked until just firm raises blood sugar less than soft pasta. Cooked and cooled starch becomes partly resistant.
- Fat, protein and acid. Eating carbohydrate with protein, fat or vinegar lowers the response of the whole meal. Small studies suggest vinegar helps, though the effect is modest.
The limits of GI and GL
Neither number is a complete guide. Both come from small tests, mostly in healthy volunteers, and individual responses to the same food can differ a lot. GI says nothing about nutrients, so a low-GI food can still be heavily processed or high in saturated fat. Foods with no carbohydrate, such as meat, fish and eggs, have no GI at all, and that does not make them better or worse by default. Large cohort data, including the Nurses' Health Study analysis by Salmeron and colleagues, linked a high glycemic load with a higher risk of type 2 diabetes, especially when cereal fiber was low, but diet quality as a whole matters more than any single number.
How the recipes on this site apply these ideas
Every recipe here is built to keep the glycemic load low without asking you to calculate anything. The rules are simple:
- No sugar in any form: no white or brown sugar, honey, maple syrup or agave. Sweet recipes use unsweetened cacao, spices, berries and a few drops of liquid stevia if wanted.
- No wheat flour, bread, wheat pasta or couscous. Chickpea flour, almond flour, psyllium, chia and lentil or chickpea pasta take their place.
- No dates, dried fruit or fruit juice, and no high-load fruit such as ripe banana, mango, grapes or pineapple. Fruit comes from berries, apples and citrus in modest portions.
- Starch comes mainly from beans, lentils, chickpeas, pearl barley and small portions of rolled oats, always with protein, fat or fiber on the same plate.
Browse the full recipe collection or start with the guides for prediabetes, type 2 diabetes, PCOS and fiber. The main insulin resistance guide explains how everything fits together.
Frequently asked questions
Is a low glycemic index always healthier?
No. The number only describes how quickly carbohydrate raises blood sugar. Ice cream and some chocolate bars have a modest GI because fat slows digestion, yet they are not good everyday foods. Use GI alongside fiber, protein and overall food quality.
Which fruits are best with insulin resistance?
Berries, apples, pears and citrus fruit have a low glycemic load in normal portions. Dried fruit, dates and fruit juice pack a lot of sugar into a small volume, so their glycemic load is high.
Are oats and barley low GI?
Pearl barley is low. Rolled oats sit around the low to medium border, so they work best in small portions with protein and nuts, as in the cinnamon walnut oatmeal here.
Do I need to count glycemic load?
Not for most people. Choosing beans, lentils, vegetables, nuts, fish, eggs and berries, and leaving out sugar and refined flour, already gives a low glycemic load without any arithmetic.
References
- Jenkins DJ, Wolever TM, Taylor RH, et al. Glycemic index of foods: a physiological basis for carbohydrate exchange. Am J Clin Nutr. 1981;34(3):362-366.
- Atkinson FS, Foster-Powell K, Brand-Miller JC. International tables of glycemic index and glycemic load values: 2008. Diabetes Care. 2008;31(12):2281-2283.
- Atkinson FS, Brand-Miller JC, Foster-Powell K, et al. International tables of glycemic index and glycemic load values 2021: a systematic review. Am J Clin Nutr. 2021;114(5):1625-1632.
- Salmeron J, Ascherio A, Rimm EB, et al. Dietary fiber, glycemic load, and risk of NIDDM in men. Diabetes Care. 1997;20(4):545-550. And Salmeron J, Manson JE, Stampfer MJ, et al. Dietary fiber, glycemic load, and risk of non-insulin-dependent diabetes mellitus in women. JAMA. 1997;277(6):472-477.
- University of Sydney. Glycemic Index Research Service and GI database, glycemicindex.com.
This article is educational and is not medical advice. Talk to your doctor or dietitian before changing your diet or medication.