Glycemic Index

What is Glycemic Index ?

Glycemic Index is a number that shows effect of a food item in rising the blood glucose level. In short Glycemic Index is known as GI. A GI value of 100 is given to pure Glucose.

How was Glycemic Index invented ?

1980-81 Dr David J. Jenkins was researching on foods that can be best for diabetic people. During his research he invented the term Glycemic Index and calculated it values for different food items.

Glycemic Index and Glycemic Load

Glycemic Index is a simple value given to a food item, it does not take into account the amount of food consumed by a person. Therefore a related measure Glycemic Load (GL) is calculated by Multiplying the Glycemic Index (GI) of the particular food item with the amount of carbohydrate in the serving. Sometimes the GI and GL values differs a lot. For example Watermelon has a high GI but low GL for the quantity normally consumed. While Fructose has low GI, but high GL if large quantity in consumed.

Limitations of Glycemic Index

Glycemic Index generally depends on the carbohydrate content of the food item. If we talk about Steak, which has no carbohydrate but very high protein value, has no Glycemic Index due to absence of carbohydrate. But if it does not have Glycemic Index, it does not mean that it will not rise blood sugar level. 50% of protein in Steak can be converted to Glucose if very little to no carbohydrate is consumed with it. Therefore some nutrition experts use "Insulin Index" for food comparison instead of Glycemic Index. Insulin Index measures the amount of insulin released by our body after consumption of that food item.
Insulin Resistance: The reason behind Diabetes
Glycemic Index are not considered accurate in some cases. One GI value is given to a particular food item, but in reality the variations in same food item can vary its effect on blood glucose level. The ripeness and cooking methods can easily change that value. One example of such food item is Potato, which range from very moderate to high GI value.

How GI of a food item is calculated

The glycemic index of a food is defined as the incremental area under the two-hour blood glucose response curve (AUC) following a 12-hour fast and ingestion of a food with a certain quantity of available carbohydrate (usually 50 g). The AUC of the test food is divided by the AUC of the standard (either glucose or white bread, giving two different definitions) and multiplied by 100. The average GI value is calculated from data collected in 10 human subjects.

Usually GI is used only for foods with carbohydrates. Those foods which are rapidly digested and release glucose rapidly into blood stream have a higher GI value, while those food items which are digested slowly and release glucose gradually have a lower GI value. Therefore a lower GI value of food suggests that its slow in digestion.

Glycemic Index Table for Different Food Items

ClassificationGI RangeFood Items
Low GI55 or lessfructose; beans (black, pinto, kidney, lentil, peanut, chickpea); small seeds (sunflower, flax, pumpkin, poppy, sesame, hemp); walnuts, cashews, most whole intact grains(durum/spelt/kamut wheat, millet, oat, rye, rice, barley); most vegetables, most sweet fruits (peaches, strawberries, mangos); tagatose; mushrooms; chilis
Medium GI56–69white sugar or sucrose, not intact whole wheat or enriched wheat, pita bread, basmati rice, unpeeled boiled potato, grape juice, raisins, prunes, pumpernickel bread, cranberry juice,regular ice cream, banana
High GI70 and aboveglucose (dextrose, grape sugar), high fructose corn syrup, white bread (only wheat endosperm), most white rice (only rice endosperm), corn flakes, extruded breakfast cereals, maltose,maltodextrins, sweet potato (70), white potato (83), pretzels, bagels

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