Glycemic index offers information about how foods affect blood sugar and insulin levels. The lower the glycemic index, the less the food will cause sharp elevations in blood sugar and a subsequent rise in insulin levels. Research has shown that chronically increased insulin levels can lead to insulin resistance, which has been correlated to the development of diabetes and metabolic disorders. Furthermore, obesity and cardiovascular disease have also been correlated to poor blood sugar and insulin regulation.
The glycemic index of a food is calculated by giving a sample group of people a test food that contains 50 grams of carbohydrates and then monitoring their blood glucose levels before, during and after consumption. The blood glucose levels are then compared to those recorded when that same sample group is given a control food (usually a dose of pure glucose equal to 50 grams of carbohydrates). The blood glucose reaction to the control food is given a value of 100; the reaction to the sample food is expressed as a percentage compared to the control. For example, a baked potato has a glycemic index of 76, which means your body’s blood glucose response to the carbohydrate in a baked potato is 76% of your body’s blood glucose response to the same amount of carbohydrate in pure glucose.
While glycemic index provides good information on how various foods affect blood glucose levels and insulin release, it does not take into consideration serving size. All glycemic indices are based on 50 grams of carbohydrates and not on how much of a particular food you are consuming in a meal. For a more practical measurement on how foods affect blood sugar in the context of a meal, glycemic load is a more appropriate value.
To explain this simply, while watermelon might have a high glycemic index, the amount of watermelon a person would have to eat to equal 50 grams of carbohydrates is often much more than a person would eat in a single serving. Glycemic load is a measurement to simultaneously describe the quality (glycemic index) and realistic quantity of carbohydrates in a meal.
The table below is adapted from the Linus Pauling Institute and illustrates the difference between glycemic index and glycemic load.
Also, visit www.glycemicindex.com for more information regarding the glycemic index and glycemic load of various foods.
- The Linus Pauling Institute http://lpi.oregonstate.edu/infocenter/foods/grains/gigl.html
- Dr Tim Irving DC, LMT, Nutritionist: A Little bit about the Difference between the Glycemic Index and the Glycemic Load (lecture)