The Glycemic Index is a classification of carbohydrates on a scale from 0 to 100 according to the level to which they raise blood sugar levels after eating.
High GI indicates the food is rapidly digested and absorbed, resulting in significant fluctuations in blood sugar levels.
Low-GI foods, being slowly digested and absorbed, result in gradual rises in blood sugar and insulin levels which is beneficent for health.
However, the impact of food on the blood sugar also depends on other factors such as: ripeness, content of fat, fiber, how processed the food is, cooking time, time of day, blood insulin levels and the individual time necessary for digestion.
The Glycemic Index must be used as informative for health control.
High GI level foods will result in marked fluctuations in blood sugar levels, which are not healthy because of the stress they place on the body determining the pancreas to secrete insulin to drop blood-sugar levels.
One of the undesirable effects of raised insulin levels is that it inhibits the release of growth hormones which will eventually depress the immune system.
Low Glycemic Index value is less than 55.
GI values between 55 and 70 are considered intermediate.
High Glycemic Index value is higher than 70.
Here are some examples of values for food GIs:
|Spaghetti, protein enriched||Low||27|
|Spaghetti, whole wheat||Low||37|
|Ravioli, meat filled||Low||39|
|Multi grain bread||Low||48|
|Porridge, non instant||Low||49|
|Whole grain bread||Low||50|
|Oat bran cereals||Medium||55|
|Spaghetti, durum wheat||Medium||55|
|Pita bread, white||Medium||57|
|Shredded wheat cereals||Medium||69|
|Whole meal bread||Medium||69|
|Rice pasta, brown||High||92|
|Dairies||Yogurt low-fat (sweetened)||Low||14|
|Apricots (tinned in syrup)||Medium||64|
|Lettuce, all varieties||Low||15|
|Low-fat yogurt, artificially sweetened||Low||15|
|Peppers, all varieties||Low||15|
|Young summer squash||Low||15|
|Soya beans, boiled||Low||16|
|Kidney beans, boiled||Low||29|
|Lentils green, boiled||Low||29|
|Haricot beans, boiled||Low||38|
|Tomato soup, tinned||Low||38|
|Lentil soup, tinned||Low||44|
|Baked beans, tinned||Low||48|
|Kidney beans, tinned||Low||52|
|Lentils green, tinned||Low||52|
|Black bean soup, tinned||Medium||64|
|Green pea soup, tinned||Medium||66|
|Potato, micro waved||High||82|
|Chocolate bar — 30g||Low||49|
|Jams and marmalades||Low||49|
|Table sugar (sucrose)||Medium||65|
The GI table does not include foods that do not contain carbohydrate (like fresh meat, chicken, fish, eggs and cheese). There are only processed foods containing meat and flour.
For high GI foods the advice is that they should be eaten (if at all) together with foods with a low GI. Thus, the GI value of the meal is lowered. However, for optimum nutrition, it would be preferable that these foods are replaced by lower GI foods.
The glycemic index informs on how a food raises blood sugar levels, not how much sugar is in the food. The amount of carbohydrate also affects blood glucose level. For this purpose scientists have developed the concept of Glycemic Load (GL). It describes the quality (GI) and the quantity of carbohydrate in a meal. The glycemic load is calculated by multiplying the grams of carbohydrate in a serving of food by that food's glycemic index. Thus, foods with a high level of water or air in their structure will not cause a steep rise in the blood sugar even if their glycemic index is high.
There are also other factors that influence the raise in blood sugar determined by carbohydrates:
- Physical form — the finer a grain is ground the faster the digestion, the higher the GI.
- Fiber content — high fiber content results in slower digestion and thus slower release of sugar molecules into the bloodstream.
- Fat and acid content — the higher the fat or acid content the slower the carbohydrates' conversion into sugar.
- Ripeness — ripe fruits and vegetables usually have more sugar-higher GI index- than unripe ones.
- Starch — starch configuration differs from case to case - some are easier to break into sugar molecules than others. For example, the starch in potatoes is quickly digested and absorbed into the bloodstream.
- Cooking procedure and combinations — the way of cooking influences directly the GI (e.g. when baking a potatoe, starches become more accessible to the digestive system). When combined with fat, the GI decreases, as carbs turn into sugar more slowly.