What do the Glycemic Index numbers mean?

The Glycemic Index (GI) was developed to use as an aid in making better food choices that will help keep your blood sugar levels more steady instead of allowing high peaks after eating certain types of foods (carbohydrates) that are absorbed quickly and cause the blood sugars to rise rapidly. In other words, high Glycemic Carbohydrates are carbs that result in a quick rise in blood sugar. As a starting point a piece of plain white sandwich bread was arbitrarily given an index number of 100.

Then various other foods have been given a relative rating based on the amount of effect they (or more precisely the carbohydrate in them) have on blood glucose levels and if they trigger the release of insulin.

A GI of 55 is regarded as the point at which insulin will be released. It is useful as an indicator of which foods will produce a spike in blood sugar, and which ones (with a lower or zero rating) will break down over a longer period of time and be more gradually released into the blood. In short, the higher the GI rating, the higher the blood glucose will be after consuming the food. A high GI rating is 70 or more, a medium GI is 56 -69, and low GI is 55 or less. When a low GI food is combined with a food of a higher rating, the overall effect will be to lower the GI of the food with a higher rating. Adding fiber also helps lower the glycemic index and makes you feel fuller.

Choosing low GI carbs - the ones that produce only small fluctuations in our blood glucose and insulin levels - is the secret to long-term health - reducing your risk of heart disease and diabetes and is the key to sustainable weight loss.

Some example low-GI carbs are:

Oatmeal = 49
Rice, brown = 55
Popcorn = 52
Banana = 55
Ice cream, low fat = 50
Chocolate = 49
Green peas = 48
Grapes = 46
Orange Juice = 46
Orange = 44
Apple = 38
Pear = 38
Spaghetti, al dente, boiled = 41
Yogurt (artificial sweetener) = 33
Milk, skim = 32
Bell peppers = 10
Grapefruit = 25
Whole Wheat pasta = 37
Soy beans = 18
Peanuts = 14
Spinach = 15
Turnip greens = 15
Lettuce = 10
Watercress = 15
Zucchini = 10
Celery = 15
Cucumbers = 15
Dill pickles = 15
Broccoli = 15
Onions = 10
Tomatoes = 15

On the other hand, here are some high-GI carbs (to avoid):

Pretzels = 83
Jelly beans = 80
Waffles = 76
Donut = 76
Corn chips = 72
Watermelon = 72
Rice, white, short grain = 72
Wheat bread, white = 70

Medium GI carbs (enjoy in moderation):

Pineapple = 66
Rye Kernel bread = 65
Raisins = 64
Potato, white, boiled = 62
Pizza, cheese = 60
Wheat - 100% stone Ground Wheat = 59
Pita bread, white = 57
Rice, white, long grain = 56