In 1981 researchers David Jenkins and Thomas Wolever of the University
of Toronto published a study suggesting that the "glycemic index"
of foods be used to classify carbohydrates rather than the traditional
"simple" and "complex" system.
Contrary to traditional belief, the study found that complex carbohydrates
were actually digested faster than simple carbohydrates. Therefore, complex
carbohydrates increased blood sugar much faster than simple carbohydrates.
Glycemic Index
Glycemic index (or GI) is a ranking of how fast a given food triggers
a rise in blood sugar level. The developers of the glycemic index used
pure glucose as the standard, giving it a rating of 100. Therefore, the
closer a particular food is to 100, the higher its glycemic index.
All foods that are ranked by GI are based on 50 grams of carbohydrates,
regardless of how much of that food it takes to reach 50 grams.
High |
GI of 70+ |
Moderate |
GI of 56 - 69 |
Low |
GI of 55 or less |
When high GI foods are consumed, the pancreas detects that rapid rise and
quickly pumps out a high level of insulin to balance the blood sugar levels.
The result is a sudden "crash" in blood sugar. This sudden "crash"
of blood sugar level is thought to create cravings for more carbohydrates,
resulting in a vicious cycle of abrupt ups and downs and over eating. Low
GI foods are digested slower, therefore there is a gradual rise and descent
of blood sugar when insulin is released from the pancreas lessening carbohydrate
cravings.
Glycemic Load
Although the glycemic index ranks how rapidly a particular food turns
into sugar, the serving amount is not clear. The glycemic load is a ranking
of how much a standard serving of food raises your blood sugar. The lower
the glycemic load, the less a serving of food will trigger your blood
sugar to spike.
High |
GL of 20+ |
Moderate |
GL of 11-19 |
Low |
GL of 10 or less |
The glycemic load of a particular food is calculated by multiplying the
amount of carbohydrate in a serving by the glycemic index and dividing that
number by 100. For example:
1 serving contains 12 grams of carbohydrate
(carbs less fiber)
Food item has a GI of 40
The glycemic load of the food is: 12
X 40 / 100 = 4.8 (rounded to 5)
This food has both a low GI and a low
GL
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1 serving contains 56 grams
of carbohydrate (carbs less fiber)
Food item has a GI of 45
The glycemic load of the food is 56
X 45 / 100 = 25.2 (rounded to 25)
Although this food item has a low GI of 45, the GL
is high at 25, an indication that you should be careful with portion
size and how frequently you eat this food item.
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The examples above help to explain why the glycemic load (GL) value of
a food is a better tool than the glycemic index (GI) value of a food when
evaluating the foods you eat.
Factors That Alter Glycemic Value
- Cooking process
- The amount of processing the food has undergone
- Amount of fiber present in the food
- The addition of fat/oil to food will lower values
- The addition of acid (such as lemon juice) will lower values
- The addition of vinegar will lower values
All of the above factors have the ability to alter the glycemic effects
of food.
When eating high GI or high GL foods, adding fat will slow down
the rise in blood sugar levels, i.e.: add peanut butter to a slice
of bread. |
High insulin levels are also believed to play a part in diseases such
as diabetes, high cholesterol, blocked coronary arteries, high blood pressure,
strokes, and obesity. Controlling spikes in insulin may help to alleviate
some of these health risks.
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