Glycemic Index
What is the Glycemic Index?
The glycemic index is a ranking of carbohydrates based on their immediate
effect on blood glucose (blood sugar) levels. It compares foods gram for
gram of carbohydrate. Carbohydrates that breakdown quickly during digestion
have the highest glycemic indexes. The blood glucose response is fast
and high. Carbohydrates that break down slowly, releasing glucose gradually
into the blood stream, have low glycemic indexes.
What is the Significance of Glycemic Index?
Low GI means a smaller rise in blood glucose levels after meals
Low GI diets can help people lose weight
Low GI diets can improve the body's sensitivity to insulin
High GI foods help re-fuel carbohydrate stores after exercise
Low GI can improve diabetes control
Low GI foods keep you fuller for longer
Low GI can prolong physical endurance
What is Glycemic Load?
Glycemic load builds on the GI to provide a measure of total glycemic
response to a food or meal
Glycemic load = GI (%) x grams of carbohydrate per serving
One unit of GL ~ glycemic effect of 1 gram glucose
You can sum the GL of all the foods in a meal, for the whole day or even
longer
A typical diet has ~ 100 GL units per day (range 60 - 180)
The GI database gives both GI & GL values
How to Switch to a Low GI Diet
Use breakfast cereals based on oats, barley and bran
Use "grainy" breads made with whole seeds
Reduce the amount of potatoes you eat
Enjoy all types of fruit and vegetables (except potatoes)
Eat plenty of salad vegetables with vinaigrette dressing
Glycemic Index Range
Low GI = 55 or less
Medium GI = 56 - 69
High GI = 70 or more
Measuring the GI
To determine a food's GI rating, measured portions of the food containing
10 - 50 grams of carbohydrate are fed to 10 healthy people after an overnight
fast. Finger-prick blood samples are taken at 15-30 minute intervals over
the next two hours. These blood samples are used to construct a blood
sugar response curve for the two hour period. The area under the curve
(AUC) is calculated to reflect the total rise in blood glucose levels
after eating the test food. The GI rating (%) is calculated by dividing
the AUC for the test food by the AUC for the reference food (same amount
of glucose) and multiplying by 100 (see Figure 1). The use of a standard
food is essential for reducing the confounding influence of differences
in the physical characteristics of the subjects. The average of the GI
ratings from all ten subjects is published as the GI of that food.
The GI of foods has important implications for the food industry. Some
foods on the Australian market already show their GI rating on the nutrition
information panel.Terms such as complex carbohydrates and sugars, which
commonly appear on food labels, are now recognised as having little nutritional
or physiological significance. The WHO/FAO recommend that these terms
be removed and replaced with the total carbohydrate content of the food
and its GI value. However, the GI rating of a food must be tested physiologically
and only a few centres around the world currently provide a legitimate
testing service.
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