What is the glycemic index?
When you eat bread, rice, fruit or anything else with carbohydrate, your body breaks the carbs down into sugars that pass into your blood. Some foods do this fast, others slowly. The glycemic index puts a number on that speed. It compares a food with pure glucose, which is set at 100. An apple, with a GI of 44, raises blood sugar a little less than half as much as the same amount of carbohydrate eaten as glucose.
GI values are measured in people, not calculated. Under the international standard method described by the University of Sydney, which maintains the GI database used below, 10 or more healthy people eat a portion of the food that contains 50 grams of digestible carbohydrate. Their blood sugar is measured over the next two hours and compared with their response to 50 grams of glucose. The average across the group is the GI of that food.
Foods are grouped into three bands. A GI of 55 or less is low, 56 to 69 is medium and 70 or more is high. Low GI foods are digested and absorbed slowly, high GI foods quickly. That is where the idea of slow carbs and fast carbs comes from.
For everyday eating, GI is a handy way to choose between similar foods. Many people find that meals built around slower carbs give them steadier energy through the morning or afternoon and keep them feeling full for longer. A bowl of oatmeal made from rolled oats (GI 51) and a bowl of instant oatmeal (GI 82) have much the same ingredients, yet the traditional version is digested far more slowly.
Two things to keep in mind. First, only foods with a meaningful amount of carbohydrate have a GI. Meat, fish, eggs and oils have little or none, so they have no GI value. Most nuts contain too little carbohydrate to have one either, although cashews and peanuts have been tested and score very low. Second, a low GI does not make a food healthy on its own. Potato chips (GI 57) score lower than boiled new potatoes (GI 78), mostly because of their fat. Use GI to compare foods within the same group, not to rank your whole diet.
Glycemic index vs glycemic load
The glycemic index tells you about the type of carbohydrate, not the amount. Every GI test uses the same amount of carbs, so GI says nothing about how many carbs are on your plate. That is what glycemic load (GL) adds. The formula is simple: multiply the GI by the grams of carbs in your portion and divide by 100.
Take two high GI foods. A slice of white bread has 12 grams of carbs and a GI of 71, so its glycemic load is about 9. A cup of cooked white rice has 45 grams of carbs and a GI of 70, which gives a glycemic load of about 32. Their GI is almost identical, but the rice has more than three times the glycemic load, because the portion holds far more carbs. A medium apple, with 25 grams of carbs and a GI of 44, lands at about 11. (Carb counts are from our carbs in food chart.)
The reverse happens too. The University of Sydney points out that tropical fruits such as pineapple and watermelon tend to have a higher GI, but a low glycemic load, because a normal serving contains relatively little carbohydrate. And since GL scales with the portion, doubling your serving doubles the glycemic load, whatever the GI.
In practice, use both. The GI helps you pick the kind of carb, and the portion (which is what glycemic load captures) decides how much it adds up to. If you already count carbs, you have the second half covered. Our guide on how to count carbs shows how.
Glycemic index chart: low, medium and high GI foods
The tables below give the GI of 53 common foods, sorted from low to high within each band. All values come from the University of Sydney GI database and use glucose as the reference (glucose = 100). The database lists individual test results, so many foods have several published values. For each food we used one result for its plain, commonly eaten form, tested in healthy adults, from the middle of its published range.
Treat the numbers as a guide rather than exact figures. GI values vary by variety, ripeness, processing and preparation, and foods close to a boundary can land in a different band in another test. Raisins, at 56, are a good example: other published results put them just inside the low band.
Low GI foods (55 or less)
Low GI foods are digested slowly, so their carbs reach your bloodstream gradually. Beans, chickpeas and lentils sit near the bottom of the scale, together with pearl barley, plain dairy, most whole fruits, pasta and traditional oats.
| Food | GI |
|---|---|
| Hummus | 22 |
| Cashews, salted | 22 |
| Carrots, boiled | 32 |
| Pearl barley, boiled | 33 |
| Pear, ripe | 33 |
| Milk, reduced fat | 34 |
| Chickpeas, canned | 35 |
| Plain yogurt, low fat | 35 |
| Kidney beans, canned | 36 |
| Baked beans in tomato sauce | 40 |
| Lentils, canned | 42 |
| Green peas, frozen, heated | 42 |
| Apple | 44 |
| Apple juice, unsweetened | 44 |
| Orange | 45 |
| Banana, just ripe | 47 |
| Mango | 48 |
| Spaghetti, white, boiled | 49 |
| Pumpernickel rye bread | 49 |
| Corn tortilla | 49 |
| Grapes | 50 |
| Quinoa, boiled | 50 |
| Oatmeal, from rolled oats | 51 |
Medium GI foods (56 to 69)
Medium GI foods sit in between. Many are close relatives of foods in the other two tables: basmati and brown rice are here, while jasmine rice is in the high table, and an overripe banana is here while a just ripe one is low GI.
| Food | GI |
|---|---|
| Raisins | 56 |
| Muesli | 57 |
| Banana, overripe | 57 |
| Potato chips | 57 |
| Basmati rice | 60 |
| Table sugar (sucrose) | 61 |
| French fries, oven baked | 64 |
| Beets, boiled | 64 |
| Brown rice | 65 |
| Couscous | 65 |
| Sports drink | 65 |
| Pineapple | 66 |
| Pumpkin, boiled | 66 |
| Risotto rice (arborio) | 69 |
| Special K cereal | 69 |
High GI foods (70 or more)
High GI foods are digested and absorbed quickly. Most are refined or highly processed starches: white bread, white and jasmine rice, puffed cereals and rice cakes, instant oatmeal, pretzels and potatoes, plus sweets like jelly beans.
| Food | GI |
|---|---|
| White rice | 70 |
| White bread | 71 |
| Doughnut | 75 |
| White flatbread (Lebanese bread) | 75 |
| Jelly beans | 76 |
| Mashed potato | 76 |
| Cornflakes | 77 |
| Russet potato, microwaved | 77 |
| New potatoes, boiled | 78 |
| Instant oatmeal | 82 |
| Rice cakes, caramel | 82 |
| Pretzels | 84 |
| Puffed rice cereal | 85 |
| Puffed corn cakes | 87 |
| Jasmine rice | 90 |
Source: University of Sydney Glycemic Index Database (glycemicindex.com). Glucose = 100. Each value is one published test of a common form of the food; GI values vary by variety, ripeness and preparation.
What changes a food's GI
A GI value belongs to a food as it was tested, not to the food in general. These are the main things that move the number, and most of them are in your hands in the kitchen.
Ripeness. As fruit ripens, more of its starch turns into sugar. In tests by the same lab, a just ripe banana had a GI of 47 and an overripe one 57, which moves it from the low band into the medium band.
Processing and cooking. The more a grain is milled, flaked, puffed or cooked, the easier its starch is to digest. Oatmeal from rolled oats has a GI of 51, instant oatmeal 82, and puffed rice cereal 85. Cooking time matters too: according to the University of Sydney, pasta generally has a fairly low GI, but overcooking boosts it, so cook it al dente. Temperature plays a part as well. Potatoes that are cooked and then cooled in the fridge gain resistant starch, and a vinaigrette adds acid, which slows digestion. A cold potato salad with a vinaigrette has a lower GI than potatoes served hot from the pot.
Type of starch. Even foods that look the same can differ a lot. Rice varieties contain different types of starch, and it shows: jasmine rice has a GI of 90, while basmati rice has a GI of 60.
Fat and protein. Fat slows down how quickly your stomach empties, which lowers the GI of a food. That is why potato chips (GI 57) score lower than a microwaved russet potato (GI 77). A lower GI does not make chips the better choice, though. The same effect works at the meal level: eating a high GI food together with protein and low GI carbs brings down the GI of the meal as a whole.
Fiber. Soluble fiber, found in oats, barley, beans, lentils and many fruits, forms a thick gel that slows digestion. That helps explain why pearl barley (GI 33) and lentils (GI 42) score so low. Finely milled fiber does not have the same effect, so a food can be high in fiber and still have a high GI, as many bran flake cereals do.
How CarbScanner shows GI
Looking up GI values food by food takes time, and most meals are a mix of ingredients. CarbScanner gives each meal you photograph a glycemic index rating alongside the carb count. Snap a photo of your meal and the app gives you an estimate of the total carbs, a breakdown of the ingredients and a low, medium or high glycemic index rating for the meal as a whole. It is an estimate for the whole plate, not a GI number for each food.
That lets you compare how quickly different meals release their energy, which makes it easy to choose between similar options. For packaged food, scan the barcode to look up its carbs per 100 g in the Open Food Facts database. Barcode scans show the carbs only, without a GI rating.
Used this way, GI is a practical everyday tool: swap instant oatmeal for rolled oats, pick basmati over jasmine rice, or add beans to a meal, and your carbs become slower without counting a single extra gram. If you manage a medical condition, your care team sets your targets.