What is the Glycemic Index (GI)?
It is simply a measure of how much a food will contribute to a person's
blood sugar level. The higher the index of a food item, the more
rapid the increase in blood sugar level is. 'Sweet' food like maple
syrup, chocolate, ice cream and 'starchy' food like potatoes and
donuts are rated high in glycemic index.
In contrast, food high in fiber like whole-grain rye bread and
All-Bran cereal are rated low in glycemic index.
How is the GI determined?
Glycemic index is assessed by having one or more people eat a specific
amount of a single food (usually 50 grams of digestible carbohydrate
[total carbohydrate minus fiber]) and then measuring the change
in blood sugar levels compared to the levels achieved after they
have eaten a control food such as white bread.
The average change in blood sugar levels over a set period of time
relative to the levels after consumption of the control food is
the food's glycemic index.
What is Glycemic Load (GL)?
Low GI foods that are high in carbs may be as troublesome as higher
GI foods that contain only a small percentage of carbs, if eaten
in large amounts. This is why glycemic load (GL) is important. It
ranks foods according to actual carb content (eg. in a typical portion-size),
not how fast a 50g amount of carbs raises blood sugar levels.
Harvard School of Public Health professorand researcher Walter
Willett, M.D., and his associates developed this concept as long
ago as 1997, when they published journal articles on the subject.
But it was only in their Harvard Women's Health Watch article and
Dr. Willett's new book that they have published many of the GL numbers.
How is Glycemic Load (GL) Calculated?
Glycemic load tells you how much carbohydrate is in the food, rather
than just how high or how rapidly it raises blood sugar levels.
To calculate glycemic load in a typical serving of food, divide
the GI of that food by 100 and multiply this by the useable carbohydrate
content (in grams) in the serving size.
Can you give an example of GL Calculation?
Take carrots for example, according to some GI tests, carrots have
a glycemic index of 49. They contain about 7 grams of carbohydrate
per 100g of carrots. So to calculate the glycemic load for a standard
2oz (about 50g) serving of carrots, divide 49 by 100 (0.49) and
multiply by 3.5.
The glycemic load (GL) of carrots is therefore 1.7. In some GI
tests, carrots score as high as 95 for glycemic index. Even so,
the glycemic load for a 50g serving size of carrots is still only
How Does Glycemic Index or Glycemic
Load Affect Hunger Obesity?
High glycemic diets can cause excessive calorie-intake and obesity.
For example, if we eat a high glycemic food or a high glycemic load
meal, which by definition triggers a rapid rise in our blood sugar
levels, our pancreas is over-stimulated and releases a much larger
amount of insulin.
Result? This large quantity of insulin rapidly mops up the excess
sugar in our bloodstream causing our blood sugar levels to dip quickly
below normal, causing us to feel hungry once more.
So even though we may have eaten a high calorie meal, we are induced
to feel hungry and eat again within a comparitively short time.
This process may lead to excessive calorie intake and weight gain,
possibly causing obesity.
How does GI and GL related to low-carb
diet like Metabolic Diet?
GI and GL are actually the basis for diets like Metabolic Diet and
is the ranking of foods based on the way they increase a person's
blood glucose level. A rise in blood glucose (or sugar) levels causes
a rise in blood insulin levels.
Low carb diets work on the premise that the rise in blood insulin
levels cause increased weight gain by telling your body to store
In addition, the rapid rise in blood insulin levels causes a rapid
fall, which causes hunger and, even though your body may not need
calories for energy, this causes you to eat (or overeat) which starts
the cycle all over again!
Are there Other Important Diet Considerations?
GI should not be your only criterion when selecting what to eat.
The total amount of carbohydrate, the amount and type of fat, and
the fiber and salt content are also important dietary considerations.
The glycemic index is most useful when deciding which high-carbohydrate
foods to eat. But don't let the glycemic index lull you into eating
more carbohydrates than your body can handle, particularly if you
How useful is Glycemic Load as a
It is useful in determining risks to certain types of cancer. A
large national Women's Health Study shows that women with the highest
glycemic load are nearly three times as likely to develop colorectal
cancer in the next eight years than those with the lowest glycemic
load. In an earlier study, men and women with the highest glycemic
load were 80 percent more likely to develop colon cancer compared
to those with the lowest load.
A high glycemic load may also raise the risk of uterine and stomach
cancer by 24 to more than 100 percent, compared to those with lower
glycemic loads. Researchers think that diets that repeatedly raise
blood sugar levels cause insulin levels to soar. Insulin and insulin-related
growth factors, in turn, appear to promote the development of some