The Glycemic Index. What is it?

Note: As far as fruits go, if it tastes too sweet it's generally safe to assume that it has an elevated GI.

Fruits:
apples (40)
banana (51) Ok Green
blueberries (40) Fresh
cherries (22)
grapefruit (25)
green grapes (43)
orange (51)
pears (33)
plums (24)
prunes (29)
raspberries
tomatoes
Vegetables
asparagus
beans (all)
broccoli
cabbage
carrots
garden beans
garlic
kidney beans
lettuce
mushrooms
onions
peas
peppers
spinach
squash
bitter melon
Drinks
unsweetened tea


Low GI carbs:
Bread: Whole Wheat, Multi-grain, Pumpernickel, Rye, Sourdough, Oatmeal
Corn
cooked couscous
whole grain crackers
cooked oatmeal
Pasta cooked al dente
Green, split or black eyed peas
Whole grain pita, 6"
Cooked brown rice
small whole grain roll

Other food:
barley wheat
dairy products
egg noodles
eggs
meat
nuts
steelcut slow-cooked oatmeal
seeds

Glycemic index of foods!

GI values can be interpreted intuitively as percentages on an absolute scale and are commonly interpreted as follows:

Classification and GI range

Examples:
Low GI
55 or less
most fruit and vegetables (but not potato), oats, buckwheat, whole barley, All-bran, basmati rice

Medium GI
56 - 69
sucrose, Mars bar, croissant

High GI
70 or more
corn flakes, baked potato, jasmine rice, white bread

A low GI food will release glucose more slowly and steadily. A high GI food causes a more rapid rise in blood glucose levels and is suitable for energy recovery after endurance exercise or for a person with diabetes experiencing hypoglycemia.
The glycemic effect of foods depends on a number of factors such as the type of starch (amylose vs. amylopectin), physical entrapment of the starch molecules within the food, fat content of the food and increased acidity of the meal — adding vinegar for example, will lower the GI. The presence of fat or soluble dietary fibre can inhibit carbohydrate absorption, thus lowering the GI. Unrefined breads with higher amounts of fibre generally have a lower GI value than white breads, but, while adding butter or oil will lower the GI of bread, the GI ranking does not change. That is, with or without additions, there is still a higher blood glucose curve after white bread than after a low GI bread such as pumpernickel. Many brown breads, however, are treated with enzymes to soften the crust, which makes the starch more accessible. This raises the GI, with some brown breads even having GI values over 100.
The glycemic index can only be applied to foods with a reasonable carbohydrate content, as the test relies on subjects consuming enough of the test food to yield about 50 g of available carbohydrate. Many fruits and vegetables (but not potatoes) contain very little carbohydrate per serving, or have very low GI values. This also applies to carrots, which were originally and incorrectly reported as having a high GI.[2] Alcoholic beverages have been reported to have low GI values, however it should be noted that beer has a moderate GI. Recent studies have shown that the consumption of an alcoholic drink prior to a meal reduces the GI of the meal by approximately 15%.[3]
Glycemic index (also glycaemic index, GI) is a ranking system for carbohydrates based on their effect on blood glucose levels. It compares carbohydrates gram for gram in individual foods, providing a numerical, evidence-based index of postprandial (post-meal) glycemia. The concept was invented by Dr. David J. Jenkins and colleagues in 1981 at the University of Toronto.
Carbohydrates that break down rapidly during digestion have the highest glycemic indices. Carbohydrates that break down slowly, releasing glucose gradually into the blood stream, have a low glycemic index. A lower glycemic index suggests slower rates of digestion and absorption of the sugars and starches in the foods and may also indicate greater extraction from the liver and periphery of the products of carbohydrate digestion. A lower glycemic response is often thought to equate to a lower insulin demand, better long-term blood glucose control and a reduction in blood lipids. But in fact, some foods having a low glycemic index or having very little carbohydrate cause a high insulin response or raise blood lipids. The insulin index may therefore also be useful as it provides a direct measure of the insulin response to a food.
The glycemic index of a food is defined by the area under the two hour blood glucose response curve (AUC) following the ingestion of a fixed portion of carbohydrate (usually 50 g). The AUC of the test food is divided by the AUC of the standard (either glucose or white bread, giving two different definitions) and multiplied by 100.


The effect on blood glucose from a high versus low glycemic index carbohydrate
The average GI value is calculated from data collected in 10 human subjects. Both the standard and test food must contain an equal amount of available carbohydrate. The result gives a relative ranking for each tested food.[1]
The current validated methods use glucose as the reference food, giving it a glycemic index value of 100 by definition. This has the advantages in that it is universal and it results in maximum GI values of approximately 100. White bread can also be used as a reference food, giving a different set of GI values (if white bread = 100, then glucose ≈ 140). For people whose staple carbohydrate source is white bread, this has the advantage of conveying directly whether replacement of the dietary staple with a different food would result in faster or slower blood glucose response. The disadvantages with this system are that the reference food is not well-defined, and the GI scale is culture dependent. (Click on any of the underlined words above for a more detailed description from, "Wikipedia.com")