Developed by researchers at the University of Toronto, the GI was originally created to help people with diabetes select foods that would help them better manage their chronic condition. It was well-established that stable blood sugar levels helped reduce the likelihood of developing complications associated with diabetes, such as hypoglycemia (low blood sugar) or hyperglycemia (high blood sugar), kidney disease, nerve damage, and blindness. But at the time, the conventional wisdom was that all carbohydrate foods had exactly the same effect on blood sugar, even though some studies showed that this was not the case. The researchers set out to show that some carbohydrate foods impact blood sugar more than others.
The glycemic index tells you how
fast certain foods raise blood sugar levels
In recent years, research has begun to focus on other uses for the GI. It may help guide weight-loss efforts and has potential as a component of dietary intervention for cardiovascular disease. In fact, the GI is being discussed in the mainstream media, as well as in clinical situations, in connection with the treatment and management of heart disease, stroke, and high blood pressure as well as diabetes. Although additional research is needed, scientific evidence is mounting that a diet of high glycemic-index foods may increase the risk of these and possibly other diseases.
How the Glycemic Index Works
The glycemic index ranks foods according to their immediate effect on blood sugar levels in comparison to other foods. The ranking is done by establishing the effect of 50 grams of available carbohydrate (the total amount of carbohydrate minus fiber) in a control food on blood sugar levels. The control food, originally white bread, was assigned the number 100. Once that was established, researchers tested equal amounts (50 grams of available carbohydrate) of various foods and compared blood sugar response to the control food. Any food that raised blood sugar levels more than white bread had a higher number, while foods that raised blood sugar less than white bread had a lower number.
Today, some researchers have chosen to use glucose as the control food instead of white bread. Glucose, then, is given the value of 100 and all foods are compared to its effect on blood sugar instead. When white bread is used as the control food, the GI rank of glucose is 140, since it raises blood sugar levels more than glucose. For you to use the GI index, though, it doesn't matter which method was used in testing the foods, as the idea is the same. The GI value of a food lets you compare its effect on your blood sugar relative to other foods. That can help you make wiser food choices, including choosing better, healthier carbohydrates.
There are only a few nutrition research groups in the world that have tested the glycemic response and compiled GI values. They use a very strict testing protocol to determine the GI value of each food. Let's say they want to find out the GI value of dried apricot. Researchers use a test food and a control food. In this case, dried apricots would be the test food, and white bread or glucose would be the control food. The subjects (usually 8 to 10 participants) are given enough dried apricots to provide 50 grams of available carbohydrate (approximately 27 apricot halves). Their blood sugar response is then tested and plotted on a graph every 15 minutes during the first hour and every 30 minutes during the second hour. The same procedure is used after they ingest 50 grams of available carbohydrate from glucose or white bread (the control food). The two values are compared, and the data pulled from the graph is calculated using a computer program. Finally, the average GI from all the test subjects for the test food is calculated from the collected data.
In general, low-GI foods have scores below 55. Moderate-GI foods score between 55 and 70, while high-GI foods score above 70. As you can see, the lower the GI, the slower the blood glucose response to that food. Using the GI, you can select foods that elicit a slow, steady rise in blood sugar resulting in stable blood sugar levels that keep energy high and stave off hunger.
Sometimes the glycemic index can be misleading. In the next section, learn more about how to use the glycemic index.
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