Glycemic Index

Revision as of 09:58, 18 February 2016 by User:Fellrnr (User talk:Fellrnr | contribs)

Revision as of 09:58, 18 February 2016 by User:Fellrnr (User talk:Fellrnr | contribs)

Glycemic Index (GI) is a measure of how much a food raises blood glucose (blood sugar). A food with a higher Glycemic Index raises the blood sugar more than a food with a lower Glycemic Index. The Glycemic Index value is based on a comparison with a reference food, normally either white bread or glucose.

A graph of blood glucose (sugar) for high and low glycemic index foods.


1 Calculating the Glycemic Index

The Glycemic Index is calculated by measuring blood glucose periodically after the consumption of the food. Typically the measurements are taken just before consuming the food, then at 15, 30, 45, 60, 90, and 120 minutes[1]. These measurements provide a blood glucose curve, and the area between the curve and the baseline measurement taken just before consuming the food is the "incremental Area Under the Curve" (iUAC). The iUAC is compared with the iUAC for a reference food and the value given as a percentage. So a Glycemic Index of 50 means that the food raises the blood sugar by 50% of the reference food. Generally the portion of test food consumed contains 50 grams of carbohydrate. (The iAUC is sometimes called the Post Prandial Glycemic Response or PPGC.)

2 Glycemic Index and Health

High blood glucose levels are linked to many health problems.

  • High Glycemic Index foods may be associated with obesity[2][3][4] which constitutes a major health risk[5].
  • Lower Glycemic Index foods are considered critical to preventing metabolic syndrome, as it is the high Glycemic Index foods that are risk factors, not carbohydrates as a whole [6].
  • Elevated blood glucose after consuming food (Postprandial Hyperglycemia) is an independent risk factor for heart disease and high blood pressure [7].
  • Postprandial Hyperglycemia is associated with an increased risk of stroke and heart attacks[8].
  • Postprandial Hyperglycemia is associated with the risk of death in both diabetics and the overall population, independent of age, blood pressure, cholesterol, body mass index, and smoking habit [9].
  • Lower Glycemic Index foods may improve HDL (Healthy) Cholesterol levels[10][11].
  • Elevated blood glucose and insulin are associated with cancers of the colon[12][13][14], breast[15], and prostrate[16][17][18]. It's been suggested that the high mortality rate from most cancers in obese subjects may be due to elevated insulin[19]
  • Diets with Lower Glycemic Index foods may help manage Impaired Glucose Tolerance (IGT)[20]
  • IGT is a risk factor for Type 2 Diabetes, with estimates that 70% of those with IGT will eventually develop Diabetes[21], with 5-10% succumbing each year[22].
  • IGT is also linked with metabolic syndrome, which is the cluster of health problems including obesity, high blood pressure, non-alcoholic fatty liver disease, elevated triglycerides, and cardiovascular disease[23]. (Note that while glucose lowering drugs may help prevent the conversion of IGT to Diabetes, but it's unclear if they will help prevent some of the health complications of diabetes[23].)
  • IGT is a risk factor for liver cirrhosis[24] and survival rates for those with liver cirrhosis[25].

3 Simple and Complex Carbohydrates

At one time, it was believed that "simple carbohydrates" had high Glycemic Index, while "complex carbohydrates" had lower Glycemic Indexes[26]. The difference between simple and complex carbohydrates is based on the chemistry of the carbohydrate molecule, with small molecules like sugar considered "simple" and big molecules like bread considered "complex". This division into simple and complex is unfortunately crap (biochemistry term meaning 'not useful'). The digestion of carbs is a sophisticated system that does not follow this simple division. Some simple carbs (Fructose) are very slow to digest, whereas some complex carbs (maltodextrin) are very easy to digest. For instance, white bread (a "complex" carb, GI 70) has a higher Glycemic Index than table sugar (a 'simple' carb, GI 60). This is because highly refined flour in bread is more easily digested than table sugar (which is half fructose).

4 References

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  26.,, Accessed on 13 February 2016