The glycaemic index (GI) was introduced to guide food exchanges within equicarbohydrate food categories, and it expresses the glycaemic potency of the available carbohydrate component in a food relative to that of glucose. As GI is a relative value based on ‘available carbohydrate’ it cannot guide food choice for glycaemic control unless the foods are equal in available carbohydrate. Furthermore, GI cannot respond to food intake or to effects on food glycaemic potency of replacing glycaemic ingredients with non-glycaemic ingredients. The glycaemic glucose equivalent (GGE) overcomes these limitations of GI. The GGE content of an amount of food is the weight of glucose (g) that would induce a glycaemic response equal to that induced by the food. Few studies have compared GI and GGE as guides to food choice for glycaemic control, but in a direct test of the predictive validity of GGE in a group of foods of differing carbohydrate and GI, GGE predicted glycaemic potency well, whereas GI was unrelated to glycaemic effect. Furthermore, an information-processing model of the use of food information in food choice shows that GI has fundamental flaws when used outside the restriction of equicarbohydrate food exchange categories. As a general guide to food choices for the control of glycaemia GI does not satisfy the criteria predictive validity, accuracy, safety, ease of use, flexibility, sufficiency and compatability, whereas GGE does. GGE is also a scientifically precise and meaningful term with which to express glycaemic potency than is ‘glycaemic load’.