The 2008 edition of tables of GI and GL has doubled the amount of data available for research and other applications. Most varieties of legumes, pasta, fruits, and dairy products are still classified as low-GI foods (55 or less on the glucose reference scale). Breads, breakfast cereals, rice, and snack products, including whole-grain versions, are available in both high- (70 or greater) and low-GI forms. Most varieties of potato and rice are high GI, but lower GI cultivars were identified. Many confectionary items, such as chocolate, have a low GI, but their high saturated fat content reduces their nutritional value. The GI should not be used in isolation; the energy density and macronutrient profile of foods should also be considered (1
). The high correlation coefficient (r
= 0.94) between values derived from testing the same foods in normal and diabetic subjects indicates that GI values in Table A1 are relevant to dietary interventions in people with diabetes.
Although data quality has been improved, many foods have been tested only once in 10 or fewer subjects, and caution is needed. Repeated testing of certain products indicates that white and wholemeal bread have remained remarkably consistent over the past 25 years, but other products appear to be increasing in GI. This secular change may arise because of efforts on the part of the food industry to make food preparation more convenient and faster cooking. Some foods, such as porridge oats, show variable results, which may reflect true differences in refining and processing that affect the degree of starch gelatinization (9
). Users should note that manufacturers sometimes give the same product different names in different countries, and in some cases, the same name for different items. Kellogg's Special K and All-Bran, for example, are different formulations in North America, Europe, and Australia.
Assignment of GI values to foods requires knowledge of local foods. Ideally, branded product information is available because manufacturers prepare and process foods, particularly cereal products, in different ways. This variability is not unique to the GI but true of many nutrients, including saturated fat and fiber. In the absence of specific product GI information, these tables provide the basis for extrapolation. In the case of low-carbohydrate products, a GI value of 40 for vegetables, 70 for flour products, and 30 for dairy foods could be assigned.
In summary, the 2008 edition of the international tables of GI improves the quality and quantity of reliable data available for research and clinical practice. The data in Table A1 should be preferred for research and coding of food databases. The values listed in Table A2 may be helpful in the absence of other data.