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Low Glycemic Index Eating: The Science Behind the Numbers


Apr 1, 2005

How Foods Are Measured for the Glycemic Index

What’s so great about the glycemic index?

It can help you understand the impact on your blood glucose levels by how quickly or how slowly your body digests the carbohydrates you eat. But how can you know the rate of digestion of a particular carbohydrate food?

The glycemic index spells it all out for you.

Thanks to dedicated scientists in several countries throughout the world, a specific protocol is followed in research laboratories to test the rate of digestion of certain carbohydrate foods.

Here’s what they do:

1. Eight to 10 volunteers are chosen to participate for each food to be tested. They are instructed to arrive at the research lab in a fasting state. Their fasting blood glucose levels are measured.

2. They are then given a specific amount of the test food. The actual amount varies from food to food, but it must be equivalent to either 25 or 50 grams of carbohydrate.

3. The volunteers’ blood glucose levels are measured and recorded every 15 minutes during the first hour and every 30 minutes during the second hour. (If the volunteer has diabetes, blood samples are measured over a period of three hours.)

4. All recorded values are plotted on a graph, and the area under the resulting curve is calculated by a specialized computer program.

5. The volunteers’ responses to the test food are compared with their responses to the reference food (either white bread or glucose), which were previously measured and recorded in exactly the same way. In fact, these responses are tested two or three times on different days and an average is calculated. This average value minimizes the effect of day-to-day variations in the volunteers’ blood glucose responses.

6. Once all the values of all the volunteers are averaged, the glycemic index (GI) value of that food is established and added to the list. At present, more than 600 carbohydrate foods have been tested this way.

The glycemic index attests only to the quality of a carbohydrate based on the time it takes for its digestion. Foods with a high GI value (known as “gushers”) are digested more rapidly into glucose, causing a rapid rise in the blood glucose level. Those foods with a low GI value (“tricklers”) are digested more slowly, resulting in a smaller, more sustained excursion of glucose into the bloodstream.

But, as we know all too well, how much carbohydrate one eats also affects one’s glycemic control. You’ve probably experimented with how much pumpkin pie or mashed potatoes you can “get away with” on Thanksgiving Day. By keeping your eye on portion sizes, you are addressing your “glycemic load,” that is, the actual amount of glucose that enters your blood after eating a particular amount of a particular carbohydrate.

A nice perk of using the glycemic index is that if you are a “volume” person, who likes to eat large portions, knowing which foods enter the bloodstream slowly gives you an edge. Choosing your foods carefully with help from the glycemic index will help you maintain more controlled blood glucose levels. But a word to the wise: Don’t go overboard, because the calories that accompany those low GI carbs add up, and when they are too many, they’re too many, no matter how healthy your food choice.


The Glycemic Index ranks carbohydrate foods on a scale of 0 to 100 based on their impact on BG levels after consumption. The higher the glycemic index, the more rapid the spike in BG levels.

Low: 0 to 55
Peanut butter 14
Pasta 44
Baked beans, canned 48
Intermediate: 56 to 69
Raisins 56
Instant oatmeal 66
Pancakes 67
High: 70 or more
Bagel 72
Cheerios 74
Pretzels 83
Cornflakes 92


Categories: Blood Glucose, Diabetes, Diabetes, Food, Glycemic Index & Carb Counting, Nutrition Advice



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