The GI of foods is determined using a food portion containing 50 g available carbohydrate. Although they have the same GI, a portion of two different foods with varying carbohydrate contents per 100 g may have a different impact on glycaemic response (Table 3.1). Therefore the concept of glycae-mic load (GL) was introduced to help understand the relationship between the glycaemic response to foods and health outcomes in epidemiological studies (Salmeron et al., 1997a,b). GL is formally the product of the available carbohydrate content and the GI of a food. It is a measure of the quantity and quality of the carbohydrate in the food item and has units of weight (g). Foods with the same GL will theoretically produce the same glycaemic response even if their GI is different (Livesey, 2003).
Which foods should be considered high GI and which should be considered low GI? Professor J. Brand-Miller and her team from the University of Sydney have proposed the following cut-off levels, where the reference food is glucose, with a GI of 100 (www.glycemicindex.com):
In order to calculate the glycaemic effect of the whole diet, the GL is used. The GL of the diet of one day can be calculated by adding together the individual GLs of all meals consumed over the day. A typical diet of one day will have a GL of about 100. A diet with a daily GL of less than 80 would be considered as low GI and one with a GL of above 120 as high GI.
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