Understanding: Glycemic Index and Glycemic Load

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Both of these terms relate to how your body responds to the food that you eat, in terms of blood sugar.

Glycemic Index
The glycemic index (GI) is defined as the measure of the power of foods to raise blood sugar (glucose) levels after being eaten.  The glycemic index is measured on a scale of 1-100.  Foods with a lower glycemic index raise your blood sugar less than when you consume a food with a higher glycemic index rating.  In other words, a lower glycemic index tends to be better than one that is higher.

Pure glucose has a glycemic index of 100, and is used as the comparison for other foods.  Here are some examples:  the glycemic index of jelly beans is 80, and rice cakes is also 80.  Corn flakes have a glycemic index of 83.  A banana is 56, while an orange is 43.  Sweet potato and yams are 54 and 52, while breads range from 60-90.  Broccoli and spinach, meanwhile, have a glycemic index of 6.

The glycemic index of a food is determined by testing the actual blood glucose measurements of a group of people after that food is eaten.  This is because there are many factors that affect a particular food’s glycemic index – not just the amount of carbohydrate it contains.

The Glycemic Index was developed in 1981.  Since then, over 2,500 foods and food-like substances have been tested to examine their effect on people’s blood sugar.  In doing this research, it was found that many other factors besides the amount of carbohydrate in the food were important in how the food affected blood sugar levels.

What else affects the GI of a Food?

  • The type of carbohydrate present
  • The amount of fiber in the food
  • The amount of processing the food has been through
  • The speed of digestion
  • The speed of absorption by your body

Glycemic Load
Glycemic Load is a measure that uses the Glycemic Index and combines it with the amount of a food that you have eaten. The formula for Glycemic Load is simple:

A food’s Glycemic Index, times grams of carbohydrate in the food consumed, divided by 100.

GL*grams carbs/100.

The Glycemic Index described above is a measure of how a particular food is digested, absorbed, and ultimately travels through your blood as glucose.  An aspect that is absent from this description is how much of that food that you eat and the impact of the total amount of sugar entering your body.  In other words, Glycemic Index describes how much of a particular food ends up as glucose in your blood (blood sugar), but it needs to be expanded upon to describe how much of a particular food have you eaten.

Glycemic load was developed at Harvard in the 1990′s to improve upon the concept of the Glycemic Index.  A lower Glycemic Load value refers to a lower total load of glucose in your blood stream.  For Glycemic Load, 10 or less is low, medium is 11-19, and a Glycemic Load of 20 or greater is high.  A range of Glycemic Load daily values is 60 on the low end to anywhere as high as 180 on the high end.  A best practice is to keep your total Glycemic Load under 100 per day.

Glycemic Load Tool:  See this index for more examples of other common foods’ glycemic loads.

Important Considerations:

The Glycemic Index and Glycemic Load of a food, and of your overall diet, is an important aspect of the quality of your nutrition.  High blood sugar levels are associated with all of the chronic diseases, most notably obesity, heart disease and diabetes, but high blood sugar levels are also associated with several types of cancer.  However, a holistic approach is always critical to ensure that your fuel contains all of the essential elements your body needs.  Total energy consumption, nutrient content, variety, and food quality are all key aspects to understand, along with your fuel’s affect on your blood sugar.

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