The glycemic index, or GI, is a ranking tool that focuses on the glycemic loads of foods. The GI uses a numeric scale from zero to 100 to describe how much each food alters blood sugar levels. One 5-ounce tomato has a GI of less than 15, which is low.
A Low-GI Food
Foods that have a ranking closer to 100 are considered high-GI foods, and foods that have a ranking closer to zero are considered low-GI foods. At less than 15, tomatoes are considered a low-GI food. This means that the tomato is digested and absorbed more slowly than high-GI foods. Eating a tomato will raise blood sugar and insulin levels gradually rather than rapidly. Because of this, the tomato would be an appropriate vegetable to include in a low-GI diet plan, which might be prescribed for someone who has diabetes or difficulty controlling his weight.