Using the Glycemic Index

Two important concepts will help you predict and control your blood sugar responses to your carbohydrate intake. The first of these is the glycemic index (GI). To their credit, the Joslin Center’s guidelines are the first in the United States to actually mention the concept of GI in better meal planning. The GI value of a particular food is simply the effect it has on your blood glucose levels. When you consume a carbohydrate, your body breaks it down through digestion and then absorbs it. The more rapidly it does so, the sooner the absorbed end products of carbohydrates (mainly glucose) get into your bloodstream.

GI values are usually scaled from 0 to 100, with glucose being the most rapidly absorbed–its GI value is 100. If a food has a high GI value, then your BG will rise more rapidly after eating it; a lower number means that the food causes less of an immediate increase. While the actual range for each GI category may vary somewhat, “high-GI” foods are usually considered to be those with a GI value of 70 or more. These foods cause rapid rises in blood sugars that are even harder to control if you have diabetes or insulin resistance.

Most of the foods in the high-GI category contain large amounts of highly refined flour or added sugars, including most ready-to-eat breakfast cereals, pretzels, sugary candy, and bread. White potatoes, though not a processed food, also fit into this list because they are digested so rapidly. To deal with the influx of glucose from carbohydrates with higher GI values, your pancreas must be able to respond by releasing a large amount of insulin to take the resulting glucose out of your bloodstream and into cells around your body. Unfortunately, most people with diabetes lack the ability to respond to these glucose spikes with adequate amounts of insulin, as do many people with pre-diabetes and insulin resistance.

Other carbohydrate sources cause less of a spike in your blood sugar levels and are generally easier for your body to handle–depending on how much of them you eat. “Medium-GI” foods such as sweet potatoes, rice (white or brown), oatmeal, and white sugar have GI values in the range of 55 to 70. Any food with a GI value less than 55 is considered “low-GI”; examples are most whole fruits (since the GI value of fructose is not that high–even though it’s a simple sugar), dairy products, legumes (beans), and pasta (white or whole-wheat). A more comprehensive list of GI values of common American foods taken from the International Table of Glycemic Index and Load Values (2002) can be found online at

More on this topic to come next week…


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