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The Glycemic Index

Glycemic Index… glycemic load… good carbs… bad carbs… no carbs. It’s all so confusing, isn’t it? I get lots of questions about which carbs may raise blood glucose and which may not. In truth, all carbohydrate-rich foods raise blood glucose, but research shows that some have a more dramatic effect than others. The glycemic index attempts to identify which foods spike blood glucose and which foods have a more gradual release of glucose.

Understanding the glycemic index (GI)?

The GI ranks carbohydrate-containing foods from 0 to 100 – the higher the number, the bigger the rise in blood sugar; the index measures each food in a portion containing 50 grams of carbohydrate. A food that is slowly digested and absorbed, such as apples or chickpeas, causes glucose to move more slowly into the bloodstream, while a food that moves quickly through the digestive system, such as white bread or gummy bears, cause glucose to flood more quickly into the bloodstream. You can search a database at www.glycemicindex.com to learn which foods have high (>70), medium (56 – 69) or low (<55) GI scores. So it may sound easy: just pick the foods with low GI scores, and your blood glucose will stay steady. Unfortunately, it’s not that simple.

One problem with the GI is that it doesn’t consider the portion size of a food. Our servings don’t usually contain exactly 50 grams of carbohydrate. Sometimes 50 grams is a huge serving: imagine nine cups of cherry tomatoes or four cups of milk. Other times 50 grams is more typical: a single bagel or a little more than a cup of rice. This is one reason that using the GI alone doesn’t seem to help my patients. A better way to predict the effect of a serving of carbohydrate-containing food is to use the glycemic load. The Glycemic Load (GL) considers both the glycemic index and the amount of carbohydrate. Thus, the GL varies depending on the amount of milk or rice you consume. Below is the simple formula for calculating the GL.

·    Glycemic Load (GL) = (GI x grams of carbohydrate eaten)/100

·      Low GL: <10

·      High GL: >20

My friend and colleague Toby Smithson, RD, CDE, spokesperson for the Academy of Nutrition and Dietetics and founder of DiabetesEveryDay.com, has type 1 diabetes. She uses the GL to help manage her blood glucose. “Monitoring the total amount of carbohydrate is most important,” Toby says. “The amount of carbohydrate has a greater effect on blood glucose than the source of carbohydrate, so portion sizes matter a lot!” Lentils and boiled sweet potatoes, for example, both have low GI scores, but if you eat a huge portion of either, your blood glucose may go high. Toby doesn’t avoid high GI foods completely, but she does combine them with lower-GI foods to help even out the effect. “The most important thing I learned is that all foods can fit,” says Toby. “It’s a matter of monitoring your blood sugar patterns and using that information to try to achieve better blood sugar readings.”

Another problem is that neither the GI nor the GL indicate if a food is actually nutritious or not. Lots of candy bars have a low score and some fruits and whole grains have high scores. Toby’s advice is to focus on choosing nutrient-dense foods (like me, she’s a registered dietitian, so “nutrient-dense” gets thrown into most of our conversations!), monitoring your carbohydrate intake and using the GL as just one more tool in your tool box. Try not to let the GI or GL distract you from the bigger picture of making healthy overall choices.

If you’d like to incorporate the GI or GL into your current diabetes meal plan, continue to count carbs, use diabetic exchanges, or stick with whatever system fits your lifestyle. Then, what Toby and I both suggest is choosing low GI foods or limiting the portion size of high GI foods most of the time. This list of swaps below may help get you started. Find more information on specific foods at glycemicindex.com.

Instead of This (higher GI/GL foods)

Consider This (lower GI/GL foods)

 White bread  Sourdough or rye bread
 Baked white potato without skin  Baked white potato with skin
 White rice  Lentils
 Soft spaghetti  Al dente spaghetti
 Corn chips  Nuts
 Raisins  Grapes
 Cornflakes  Rolled oats

Jill Weisenberger, MS, RD, CDE, is the author of Diabetes Weight Loss Week by Week, contributing editor for Environmental Nutrition, and has written for many publications including EatingWell, Diabetic Living, Her Sports + Fitness, and LifeScript. Weisenberger is a paid contributor for The DX. All opinions contained in this article reflect those of the contributor, and not of Sanofi US, its employees, agencies, or affiliates.

© 2013 The DX: The Diabetes Experience

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