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A LITTLE ABOUT THE GLYCEMIC INDEX

The glycemic index or (GI) is a way of scoring food on a scale from 0 to 100. Pure glucose is scored with the value of 100, which represents the relative rise in the blood glucose level upon digestion of the specific food. The GI of a specific food depends primarily on the quantity and type of carb it contains; but also is affected by how much the carbohydrate molecules are entrapped within the food. Fat and protein content of the food, as well as whether it is cooked also effects the GI rating.
A food is considered to have a low GI if it is scored at 55 or less; a mid-range GI is a scoring of 56 to 69, and a High GI is if the food is scored from 70 and above. 
Generally speaking the glycemic index allows you to see which foods that you eat break down at the slowest rate, and which ones break down the fastest. This information can be used as a tool to help you define your nutrition using foods that break down at a rate equivalent to your energy demands.
An example of this comparison of demand, versus supply is that a man sitting on a couch watching T.V. is not expending energy at a high rate, and would not benefit from 300 calories of pure glucose, which is scored on the glycemic index at 100, and breaks down at a very fast rate in the body. A man running at a heart rate of 170 beats per minute is using energy at a very high rate and, would not benefit much from 300 calories of Grape fruit which is scored at 25 on the glycemic index and breaks down fairly slow in the body. If you were to give the grapefruit to the man watching T.V., and the glucose to the person running, both would benefit as the energy they are consuming would be in balance with the demand of energy for their activities.
Remember, the lower the score of the food, the longer the energy from it stays in your system. The higher the score of the food, the faster it burns, and if your balance is off, you are left with either a deficit of energy, which can lead to loss of lean mass, or you are left with an overage of energy, which can lead to extra storage of body fat.
Click on the link below to gain access to a list of common foods and how they rank on the glycemic index.