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aGlycemic index (GI) is rounded to the nearest 10%.

aGlycemic index (GI) is rounded to the nearest 10%.

diet, protects from the development of type 2 diabetes. Therefore, the question is whether the rapid increase in diabetes in cultures in transition from traditional to Western lifestyle patterns is in part due to the high glycemic index of the diets eaten, in addition to the excess consumption of energy and reduced physical activity.

Calculation of the Glycemic Index

The glycemic index (GI) has been defined as the area under the blood glucose response curve for 50 g carbohydrate from the test food divided by the area under the blood glucose response curve for 50 g carbohydrate from the standard source, multiplied by 100. The standard carbohydrate source for modern assessments is white bread. In early studies, however, 50 g glucose was used rather than bread. On the 'bread scale' the glucose GI is approximately 130%. Other food GI values can be adjusted accordingly to allow direct comparison of the two scales.

The area under the blood glucose curve includes the area above the fasting level only. Any area beneath the fasting level is ignored. The incremental area under the blood glucose response curve is the sum of the areas of the triangles and rectangles. In Figure 3, A, B, C, D, E, and F represent the blood glucose increments above the baseline value (fasting level) at sequential time points, where t and T represent different time intervals between blood samples.

When the blood glucose concentration at F falls below the fasting concentration (Figure 3), only the area above the fasting level is included in the total area represented by the triangle ET, where T' represents the portion of the time interval T when the blood glucose level between E and F is above the fasting level.

TO "D

TO "D

Time

Figure 3 Schematic representation of postprandial blood glucose response (From WoleverTMS and Jenkins DJA (1986) The use of the glycemic index in predicting the blood glucose response to mixed meals. American Journal of Clinical Nutrition 43:167-172.)

Time

Figure 3 Schematic representation of postprandial blood glucose response (From WoleverTMS and Jenkins DJA (1986) The use of the glycemic index in predicting the blood glucose response to mixed meals. American Journal of Clinical Nutrition 43:167-172.)

The overall equation simplifies to Area = (a + B + C + D )t + 'DtEE

If the last blood glucose concentration F is above the fasting level, then the term (E + F)T/2 is substituted for the last term in the equation, namely E2 T/2(E + F). An example of the incremental area calculation is shown in Table 5.

Calculation of mixed meal or total day's GI Each carbohydrate component is expressed as a percentage of the total carbohydrate in the meal or day and multiplied by the relevant GI. The sum of these values represents the meal's or the day's GI.

Table 5 Example of calculation of incremental area under the blood glucose response curve for glycemic response when the last glucose value falls below baseline

Time

Corresponding

Blood

Blood glucose

(min)

letter on

glucose

increment

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