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What is the Glycemic Index and is it useful?

Written by: Martha Weintraub, MPH, MSW, RD
Fit4D Nutrition Coach









There is quite a bit of media controversy over the use of the glycemic index (GI) for blood sugar management and weight loss.  People familiar with the GI often have very definite ideas about its usefulness in making food choices but they don’t necessarily agree about this topic.  Whether you’ve been part of this debate, are curious about the glycemic index, or have never heard of this concept before, it would be a good idea to be well informed about what the GI is and how it is best used.

What exactly is glycemic index and glycemic load?

  • The GI ranks how quickly 50 grams of a carbohydrate food raises blood glucose compared to either sugar or bread.
  • Foods with a high GI will be absorbed more quickly and have a bigger impact on blood sugar levels than foods with a lower GI.  Although this sounds like it should be a clear cut measurement, it can be affected by how processed the food is, how much protein, fat, and soluble fiber the food contains, how long the food is cooked, and what other foods are eaten at the same time.
  • The biggest problem with the GI is that it is based on the effect of 50 grams of carbohydrate from a particular food, even when a normal serving may be nowhere near 50 grams.  Carrots are an example of the confusion that can arise from this issue.  One GI entry for carrots lists their GI as 92, an extremely high ranking on a scale of 1-100.  However, a typical serving of carrots contains only 5-6 grams of carbohydrate, so eating the equivalent of 50 grams of carbohydrate would mean eating over 2 pounds of carrots at one meal.  Few people would be able to say that carrots were responsible for their high blood sugar or weight gain.
  • The glycemic load (GL) was developed to avoid some of this confusion by accounting for the amount of carbohydrate consumed in a typical portion of each food.  For example the GL of a typical serving of carrots varies from 1 to 6 depending on preparation method, but any GL less than 10 is considered a low score, with less impact on blood sugars.

What are the official recommendations regarding using the Glycemic Index for glucose management?

The American Diabetes Association recommends that the GI and GL may provide some benefit in blood glucose management over the use of total carbohydrate alone.

Can the GI or GL have benefits other than glucose management?

  • Evidence for the benefit of using the GI and GL is not yet clear.  A low-GI diet has been found to improve A1c and reduce blood sugar lows compared to a high-GI diet and may improve insulin sensitivity (how efficient the body is at using insulin).
  • There is growing evidence that a low-GI diet can help with weight management as well as limited evidence that it can help improve cholesterol levels and cardiovascular disease risk as well as, but these are not yet clearly supported by research.  

How can I use the glycemic impact of foods in meal planning?

Examples of high-GI foods (rated 70 or higher) that are likely to have more of an impact on blood sugar include:

  • white bread, bagels
  • corn flakes, instant oatmeal
  • shortgrain white rice, rice pasta, macaroni and cheese from mix
  • Russet potato, pumpkin
  • pretzels, saltine crackers
  • melons and pineapple

A low GI meal plan is one based on vegetables and fruits, lean protein, low fat dairy products, beans and legumes, nuts and heart healthy oils, and whole grains.  Examples of low GI foods (55 or less) include:

  • 100% stone-ground whole wheat or pumpernickel bread
  • oatmeal (rolled or steel-cut), muesli
  • pasta, converted rice, barley, bulgar
  • sweet potato, corn, lima/butter beans, peas, legumes and lentils
  • most fruits, non-starchy vegetables (including carrots)

Foods such as animal protein and oils have no carbohydrate so have no GI ranking.  Other high fat foods may also have a low GI ranking because of the fat they contain, such as some ice creams and pastries, but that doesn’t mean they’re nutritious additions to your meal plan.

How can the GI help with menu planning?

  • Let’s look at Carla, a young woman living with diabetes, who was ready to make some lifestyle changes.  Carla had been carefully counting her carbohydrates and limiting them to 60 grams at each meal, but was not happy with her blood sugar levels or A1c.
  • She decided to use the GI list to see if it would help her manage her health more easily.  Below compares her usual breakfast to a GI alternative.
Original menu Gl menu
Small bagel 1 cup steel-cut oatmeal
Low-fat cream cheese & jelly 1 tablespoon almonds
Jelly 2 tablespoon raisins
½ cup orange juice 1 cup skim milk
  • Both breakfasts contained approximately 60 grams of carb, but the new menu was significantly lower on the GI.
  • Carla noticed right away that her blood sugars before lunch decreased to within her target range and she saw an improvement in her A1c three months later.

Is there a downside to using the GI?

  • Many people find they begin to limit their food choices to those lowest on the GI list, and for some people, the GI and GL provide more detail than needed.
  • In fact, variety is essential for good health and we need to enjoy our food choices.
  • Using the general description of a low GI meal plan as one based on vegetables and fruits, lean protein, low fat dairy products, beans and legumes, nuts and heart healthy oils, and whole grains, and avoiding processed foods and sweets, will result in an eating pattern that is low on the GI without having to constantly consult the list and check the numbers.

What’s the bottom line?

If you are looking for help in making healthy food choices, the GI or GL can be another tool to assist you in improving your meal plan and your blood sugar management.  If you are already choosing less processed, high fiber foods with lots of vegetables, you are likely to find that you’ve been following the guidelines for a low glycemic load meal plan without even realizing it!

Have you used the GI or GL in the past to help manage your blood glucose?  Did you find it helpful? We’d love to hear about your experiences!  Please share in the comments.

Where can I get more information?

For information from the American Diabetes Association about the Glycemic Index visit:|utmccn=%28referral%29|utmcmd=referral|utmcct=/&__utmv=-&__utmk=207823762

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