Glycemic Index: What’s It All About?

Some nutrition experts are talking about a concept called the glycemic index. They describe it as a good way to judge how a carbohydrate food will affect blood sugar levels — a topic that’s important to people with diabetes. Some food products even show their glycemic index on the label.

If you’ve heard about the glycemic index, have you figured out what it means to you and your diabetes nutrition plan? Maybe not. If that’s the case, this Healthy Eating article might help.

• It explains what the glycemic index is and how the indices for different carb foods are determined.
• It describes the value — and the drawbacks — of using the glycemic index for making food choices.
• It describes how to use the glycemic index in your nutrition plan.

Glycemic Index Basics

The glycemic index (from here on, we’ll call it GI) is a way to rank carbohydrate foods like potatoes, bread, rice, and pasta based on their glycemic response, or how much they affect a person’s blood sugar levels one to two hours after eating. Foods with a high GI are absorbed faster and cause a larger spike in a person’s blood glucose levels than foods with a low GI. Foods with a low GI are digested slowly so that glucose is released gradually into the bloodstream.

But where do the numbers come from? How do nutrition experts know that the GI of a bran muffin is 60 and a banana is 51? To figure out the GI, scientists compare the glycemic response to that of a reference food that contains the same amount of carbohydrates, 50 grams. The reference food is either white bread or glucose.

What do these numbers mean? The blood sugar effect of the reference food is assigned a value of 100. This table shows how the values for how the GI of foods is categorized compared to 100.

• Values 55 and below: Low GI
• Values 56 to 69: Intermediate GI
• Values 70 to 100: High GI

A baked white potato has a GI value of 93, while a baked yam has a GI value of 54. Based on this system, which vegetable would be the better nutrition choice? The yam.

The Value of GI

In theory, eating foods with a low GI will help your body cells use insulin more effectively, so the cells will take up more blood sugar to use for energy. Of course, this lowers the amount of sugar in your blood. As a result, your blood sugar levels are better controlled and if you use insulin, this can help reduce your insulin requirement.

The Other Side of the GI Story

The GI sounds like a good deal for people with diabetes. But nutrition experts are still debating the benefits of using it to help people with diabetes make food choices. Here are some of the issues they’ve identified:

• Many factors affect the GI of a food.
  • How much fiber and fat the food contains. The more of these, the lower the GI.
  • How ripe the fruit or vegetable is. The riper these foods are, the faster their carbohydrates are digested and absorbed, and the higher the GI.
  • How much the food was processed before you bought it. The more it was processed, the higher the GI.
  • How you prepare the food (raw, cooked).
  • What you eat with the food, if it’s eaten at a meal.
  • How quickly or slowly you eat the food.
• Also, blood sugar levels vary from day to day, so people with diabetes may not always respond to the same food in the same way. In addition, GI testing of foods is done in people without diabetes.
• In addition, some foods like carrots have a high GI but contain important vitamins and minerals, while foods like ice cream have a low GI but are high in sugar and saturated fat and not as nutritious as carrots.
• Glycemic index is based on a serving of food that provides 50 grams of carbohydrate. For some foods this might be a really big portion (as in the case of vegetables) or a small one (as in the case of a baked potato). To remedy this, glycemic load (GL) was introduced to provide a measure of the glycemic response of a typical serving of food. Foods with a GL of 10 or less are low GL; those with a GL of 20 or higher are high GL.
• It is extremely challenging for most people to eat only low-GI foods for any length of time.

Meal Planning With the GI

Looking at these issues, you’re probably wondering whether the GI is worth the effort. It does seem like planning a low-GI diet can be confusing and time-consuming, and it may not produce the healthiest result.

But the bottom line is that the GI can be a useful tool. However, it shouldn’t be the sole basis for your food choices. It’s better to focus on sticking to your whole program of healthy eating and physical activity to help you take better control of your diabetes.

• Aim for one low-GI food per meal. Here are some examples.

  Try … (GI)	Instead of … (GI)
  Whole-grain bread (51) Oat bran cereal (50) Baked beans (48)	White bread (70) Corn cereal (83) Mashed potatoes (83)

• Monitor your blood sugar levels before and after you eat to see how a food affects your blood sugar levels.

Remember that Glucerna SR™ products are designed specifically for people with diabetes. They contain low-GI ingredients, and their unique blend of slowly digested carbohydrates helps to minimize blood sugar peaks.

Giving the GI a Try

A little experiment may help you decide whether you think you’d find the GI helpful.

1. Pick two meals this week at which you won’t be drinking your Glucerna SR Shake — say, dinner on Tuesday and Thursday. Plan the meals to be similar, eat similar portions, but with a different carb food at each meal. Here’s an example:
   
   

   Tuesday	Thursday
   Baked chicken breast	Baked chicken breast with herbs
   Steamed broccoli with a squeeze of lemon juice	Steamed broccoli and a sprinkle of butter-flavored granules
   Mixed-greens salad with light vinaigrette dressing	Romaine lettuce with light vinaigrette dressing
   Mashed potatoes (GI, 83)	Baked beans (GI, 48)

   
   
2. Record your blood sugar levels on those two days, both before you eat and two hours after you eat.
   
   

   	Tuesday	Thursday
   After
   Before

   
   
3. Subtract the before-meal blood sugar values from the after-meal values for both meals.
   
   

   	Tuesday	Thursday
   Before
   	minus	minus
   After
   Results

   
   
4. Is your after-eating increase in blood sugar level less after the meal at which you ate the lower-GI carb food than after the meal at which you ate the higher-GI carb food?

Obviously, this is not a scientific test. And many nonfood factors can affect your blood sugar levels, like being under the weather. But if you did see a positive difference in results, it might encourage you to use the GI to help guide your food choices. Can’t hurt, might help.

Summary

• The GI ranks carb foods according to how they affect blood sugar levels one to two hours after eating. Foods with a high GI (70 and above) are absorbed faster and cause a larger spike in a person’s blood glucose levels than foods with a low GI (55 and below). GI values are determined by comparing blood sugar effects of carb foods to those of 50 grams of glucose (or an equivalent serving of white bread). The blood sugar effect of eating 50 grams of glucose is given the value of 100.
• Eating foods with a low GI may help your body cells use insulin more effectively, so the cells will take up more blood sugar to use for energy. This lowers the amount of sugar in your blood. As a result, your blood sugar levels may be better controlled.
• However, the value of GIs for making food decisions is not clear cut. Many factors can affect a food’s GI, among them how the food is prepared, how ripe it is, and what foods it’s eaten with. And an individual’s glucose response can vary from day to day. So the GI should be considered a helpful tool and not the primary basis of food decisions.