The glycemic index (GI), a numeric rating system that measures one food's ability to raise blood sugar against another's, is a handy tool if you are concerned about sugar in your diet and how it affects your health. All foods on the list are measured against pure sugar, or glucose, which has a GI value of 100. Only foods that contain carbohydrates have a glycemic index value.
Any food that has a GI value of 100, or higher, will raise your blood sugar just as quickly and easily as pure sugar. These spikes in blood sugar, over time, can increase your risk of developing heart disease, diabetes and other medical conditions. Not surprisingly, white bread, white rice, cold breakfast cereals, doughnuts, snack chips and other low-fiber carbohydrates are high on the GI list.
Vegetables, for the most part, are very low GI foods. Root vegetables, including white potatoes, sweet potatoes, carrots and parsnips, are the exception. Mashed, boiled, baked or fried white potatoes, without skin, are just as high up on the GI list as, and sometimes higher than, pure glucose. As a result, they can have the same effect on your blood sugar. Other starchy vegetables, such as peas, corn and winter squash are moderately high on the glycemic index.
Different varieties of the same vegetable can have different glycemic values. Processing, ripeness, and preparation techniques, such as slicing or dicing, also affect the GI. Ripe vegetables have a higher sugar content than unripe and therefore a somewhat higher GI value. Vegetables that are overly processed or strained after cooking can lose much of their fiber, which increases their GI value because lower fiber foods are generally digested and absorbed more quickly than higher fiber foods.
Instant potatoes 120
Baked potato without skin 98 - 120
French Fries 105
Parsnips 97
Sweet Potatoes 85
Corn 85
Rutabaga 72
Carrots 70
Baked potato with skin 69
Green Peas 50 - 70
Spinach, broccoli, peppers, onions and all other nonstarchy vegetables have GI values less than 55. Foods with low GI values can help manage type II diabetes and control weight. But the important thing to remember is that the GI value is just one measure of a food's contribution to good health and, as a stand-alone factor, may be meaningless for many people. Case in point: A chocolate bar has a GI value similar to that of a carrot or an ear of corn and yet it hardly makes the same nutritional contribution to your overall diet.
Resources:
University of Wisconsin Extension: Glycemic Index
Harvard School of Public Health: The Nutrition Source: Carbohydrates
http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/carbohydrates-full-story/index.html#glycemic-index
Jerry Sobieraj, MD, Boston Medical Center
http://people.bu.edu/sobieraj/nutrition/gi.html
Glycemic Index Foundation (searchable GI database)
http://www.glycemicindex.com/
