Hopefully we are all aware of the term glycemic index (GI), which is a measure of how quickly blood glucose (BG) levels (i.e., blood sugar) rise after eating a particular type of food. Glucose (the defining standard) has a GI of 100. The effects that different foods have on BG levels vary considerably. The GI estimates how much each gram of available carbohydrate (total carbohydrate minus fiber) in a food raises a person's BG level following consumption of the food, relative to consumption of pure glucose.
A practical limitation of the GI is that it does not take into account the amount of carbohydrate actually consumed. A related measure, The glycemic load (GL) of food is a number that estimates how much the food will raise a person's BG level after eating it. One unit of GL approximates the effect of consuming one gram of glucose. GL accounts for how much carbohydrate is in the food and how much each gram of carbohydrate in the food raises blood glucose levels. GL is determined by multiplying the GI of the food in question by the carbohydrate content of the actual serving.
For example, watermelon has a high GI, but a typical serving of watermelon does not contain much carbohydrate, so the GL of eating it is low. Whereas GI is defined for each type of food, glycemic load can be calculated for any size serving of a food, an entire meal, or an entire day's meals.
For one serving of a food, a GL greater than 20 is considered high, a GL of 11-19 is considered medium, and a GL of 10 or less is considered low. Foods that have a low GL in a typical serving size almost always have a low GI. Foods with an intermediate or high GL in a typical serving size range from a very low to very high GI.
Another practical limitation of the GI is that it does not measure insulin production due to raises in blood sugar. As a result, two foods could have the same GI, but produce different amounts of insulin. Likewise, two foods could have the same GL, but cause a totally different insulin response.
The Insulin Index is a measure used to quantify the typical insulin response to various foods. This measure can be more useful than either the GI or the GL because certain foods (e.g., lean meats and proteins) cause an insulin response despite there being no carbohydrates present, and some foods cause a disproportionate insulin response relative to their carbohydrate load.
Holt and her associates have noted that the glucose and insulin scores of most foods are highly correlated, but high-protein foods and bakery products that are rich in fat and refined carbohydrates "elicit insulin responses that were disproportionately higher than their glycemic responses." They also conclude that insulin indices may be useful for dietary management and avoidance of non-insulin-dependent diabetes mellitus and hyperlipidemia.
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