What is Glycemic Index (G.I.) and Glycemic Index Load (GI Load)?

What is GI?

Glycemic Index(GI) compares different carbohydrate foods based on their impact on the blood sugar levels. It ranks carbohydrates on a scale of 0-100 based on how much they raise the blood sugar levels after eating. Foods having high GI are rapidly digested and absorbed and therefore cause large fluctuations in blood sugar levels, lower GI foods are more slowly digested and produce gradual rises in blood sugar levels.

How is a food’s GI value determined?

After an overnight fast, a group of about 10-12 people is given a serving of a food item whose GI is to be measured. This serving contains 50gms of available carbohydrates. Available carbohydrates does not include the fiber content. After the food is been consumed blood sugar levels are measured every 15-30 minutes over a 2hour period. The results are then plotted on a graph.

Next the people are given 50gms of carbohydrates of a reference food either white bread or pure glucose. The same process is repeated. And these results are also plotted. The area under the curve for the reference food is given a value of 100. The area under the curve of the test food is then calculated as a percentage of the reference food area. Whatever that percentage is, is its Glycemic Index value. This is how GI of foods is calculated.

GI Graph Plot

GI Scale

Carbohydrates with GI value of 55 or less are rated as low, a medium value lies between 56-69 and a high value is 70 or more. Now let’s look at Glycemic Index load.

Glycemic Index GI Range

 

What is Glycemic Index Load (GI Load)?

GI load is another way to analyze carbohydrate foods. It takes into account portion sizes while GI looks only 50gms carbohydrate amounts. GI load looks at the available carbohydrates in portion size. The GI Load equation is as follows:

GI Load= (Available carbs in portion size X GI value)/100

The scale for GI load is:

High equals 20 or more, medium is 11-19 and low is 10 and below.

Glycemic Index GI Load

 

Overeating any food will dramatically increases its Load. Other things that can effect the Glycemic Index value is how it’s cooked; cooking will raise the Index value however slow cooking will not raise Index value nearly as much as fast cooking such as microwaving. The more the food is processed the higher the Glycemic value. What other types of food it is being consumed with also affects glycemic index value.

The GI and GI load is useful in relation to blood sugar level spikes but because the food has a low GI or GI Load value, does not mean the food is healthy or unhealthy. It is only just a tool, fat content, fiber content, how much the food is processed, cooking technique must also be taken into consideration.

Glycemic Index vs Glycemic Index Load

GI and GI Load of different foods:

GI Food Chart

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