What Is Glycemic Index

As expected, the level of circulating glucose increases after eating a carbohydrate-containing meal. But to what level, and will different foods having the same amount of carbohydrate result in the same increase in blood glucose? This kind of information surely would be of interest to many people, especially those managing their blood glucose levels (such as in diabetes).

As shown in Figure 4.4, the level of glucose circulating in the blood increases after eating or drinking a carbohydrate-containing food or beverage and then is reduced back toward the normal fasting level. This response is often referred to as a glucose tolerance curve and it can be used to assess how well a person's body is able to take glucose out of the blood and use it for energy and to build stores.

Since different foods will produce different glucose tolerance curve patterns, scientists developed the glycemic index. Simply put, glycemic index is a measure of the power of carbohydrate-containing foods to raise blood glucose levels after being eaten or drunk. In addition to people managing their blood glucose levels, glycemic index has become popular for many people trying to lose weight which will be discussed this in more

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Figure 4.4 Glucose levels during an oral glucose tolerance test (OGTT). Two fasting people were provided with 75 grams of glucose and their blood glucose was measured every 30 minutes for 4 hours. Note that even after 4 hours the blood glucose level of the intolerant individual is still elevated.

detail in Chapter 11. See Table 4.4 for standard levels for glycemic index and load.

Glycemic index is a measure of a food's ability to raise the level of blood glucose.

For a long time it was assumed that because starch was more structurally complex than simpler sugars, starchy foods would be digested more slowly and therefore absorbed more slowly and evenly after a meal. On the other hand, foods containing simpler sugars (for example, soda and candy) would be digested and absorbed more rapidly, leading to a faster and greater rise in blood glucose. However, the relationship between different foods and blood glucose turned out to be more complex, which is why the determination of glycemic index for individual foods has been helpful.

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