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Glycemic index (GI) is a definition used for ranking of foods according to their ability to increase blood glucose levels. High consumption of foods with high GI has a strong correlation with the development of type 2 diabetes, obesity and cardiovascular disease. The main purpose of this study was to review the available methods for measuring the GI of foods. Food GI can be measured using <i>in vivo</i> and <i>in vitro </i>methods. The <i>in vivo</i> method involves human blood testing after consumption of the food and was first introduced by Jenkins et al. (1981). For food labeling purposes, the <i>in vivo</i> method is recommended in many countries. However, it is inappropriate for research purposes, product development and quality assurance as it is costly, long, requires human intervention and lacks the necessary discriminatory power to distinguish minor differences in carbohydrate digestibility between foods. To overcome these limitations, various <i>in vitro</i> methods have been developed. The methods developed by Englyst et al. (1995) and Goni et al. (1997) are amongst the most cited methods; however recently these methods have been tailored for particular applications. They involve a series of incubations at physiological pH and temperature that imitate human digestion system. Carbohydrates are successively hydrolysed using hydrolytic enzymes including a-amylase and amyloglucosidase and then measuring the glucose content enzymatically or chemically. Recently the <i>in vitro</i> method has been automated by developing laboratory instruments but require optimization. The <i>in vitro</i> methods are criticized because they cannot mimic human digestion system in the lab and the measured GI values are only an indication of the actual glycemic response as high, low or intermediate. Further research is required to develop methods that are more suitable for measuring GI of foods for commercial purposes.