Understanding GI numbers

The glycemic index ranks the effect food has on blood sugar levels. A low-GI diet suggests foods that have low GI values. The categories are:

• Low GI: 1 to 55
• Medium GI: 56 to 69
• High GI: 70 and higher

In order to assign a rank, also called a GI value, researchers usually compare the effect of eating a food with the effect of eating sugar on blood sugar levels. Sometimes the comparison is made with eating white bread. For example, to test the GI value of cantaloupe, 10 or more healthy people eat enough cantaloupe to digest 50 grams of total carbohydrates. That is about one medium cantaloupe for each person. Over the next two hours, their blood sugar levels are tested several times. On another day, the same 10 people eat or drink 50 grams (12 teaspoons) of sugar. Again, their blood sugar levels are tested several times over two hours.

The researchers compare the results of eating sugar with eating cantaloupe to rank the effect of eating cantaloupe. The GI value for cantaloupe is 65 to 70.