Glycemic Index

The glycemic index (GI) measures how carbohydrate-containing foods affect your blood sugar level and has the following classification:

Low GI =55 or less
Medium GI = 56-69
High GI = 70 and above

This measure has proven to give valuable insights between food and health. Please note that a more precise and useful measurement of the blood glucose levels in the body is Glycemic Load because it uses the actual portion size of the meal in the calculations.

High GI food causes blood glucose levels to rise suddenly, resulting in a short-lived release of insulin in excessive amounts, followed, after 90 minutes to 2 hours, by a glucose drop. This glucose drop leads to tiredness, lethargy, nervousness and more hunger, which causes cravings for more food, usually carbohydrate rich foods. Constantly subjecting our bodies to high insulin levels results in a lower sensitivity to insulin (Insulin resistance), thereby increasing the requirements for more insulin such as in case of diabetes. A diet high in “High-GI” foods is associated with an increased risk of obesity, coronary heart disease, macular degeneration and diabetes type 2. (1)Chiu CJ, Liu S, Willett WC, Wolever TMS, Brand-Miller C, Barclay AW, Taylor A. Informing food choices and health outcomes by use of the dietary glycemic index. Nutr Rev. 2011 Apr; 69(4): 231–242. Available here.

Please note, however, that foods high in carbohydrates (foods with a high glycemic index) may be beneficial in case of strenuous physical activity, where insulin aids in placing glucose into the muscle cells for tissue repair and carbohydrate energy stores, while they are being quickly depleted.

Low GI foods release glucose slower, improving the insulin sensitivity. A low GI diet has been shown to reduce the risk of the above-mentioned diseases.

The bottom-line is that low GI foods will make you feel fuller for longer, while high GI foods will make you search for sugar snacks every two hours.

There are many benefits of a low Glycemic Index diet: weight loss and maintenance within a healthy range, improvement of the sensitivity to insulin and reduction of the risk of heart disease and high blood cholesterol. This diet keeps you full for longer, will help maintain a steady level of energy, will prolong physical endurance and will replenish your stores of energy after physical exercise. (2)Better Health Channel. Carbohydrates and the glycaemic index. Available here. (3)About Glycemic Index. Human Nutrition Unit, School of Molecular Bioscience, University of Sydney. Available here.

How glycemic index is measured?

The GI of a particular food is measured in the following way (4)About Glycemic Index. Human Nutrition Unit, School of Molecular Bioscience, University of Sydney. Available here.:

  • Since the GI response to a food can vary for person to person (5)Duyff RL. Complete food and nutrition guide. American Dietetic Association.4th Edition. 2012. John Wiley & Sons, Inc., Hoboken, New Jersey. Available here., the tests are performed on a number of people.
  • The test is performed after an overnight fasting.
  • A serving of food containing 50g of carbohydrates is used, regardless of how large the serving is. For low carbohydrate foods, the serving can be reduced to 25g of the available carbohydrates. Otherwise, the servings could get quite large.
  • The GI results of a particular food are compared against a reference (control) food: either glucose (GI 100) or white bread (GI 70). This website uses glucose as the reference for all the GI calculations since it is most widely used.
  • The GI of the same types of food varies depending on various factors such as the level of ripeness, processing methods, botanical differences or the cooking time and methods.

References   [ + ]

1. Chiu CJ, Liu S, Willett WC, Wolever TMS, Brand-Miller C, Barclay AW, Taylor A. Informing food choices and health outcomes by use of the dietary glycemic index. Nutr Rev. 2011 Apr; 69(4): 231–242. Available here.
2. Better Health Channel. Carbohydrates and the glycaemic index. Available here.
3. About Glycemic Index. Human Nutrition Unit, School of Molecular Bioscience, University of Sydney. Available here.
4. About Glycemic Index. Human Nutrition Unit, School of Molecular Bioscience, University of Sydney. Available here.
5. Duyff RL. Complete food and nutrition guide. American Dietetic Association.4th Edition. 2012. John Wiley & Sons, Inc., Hoboken, New Jersey. Available here.

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