Four Myths About the Glycemic Index

This is a guest post from Meri Raffetto, RD.

Plenty of myths or halve-truths are floating around about the Glycemic Index. Let’s just say it’s a topic that isn’t black and white. Generalized statements can make it tough to make the right choices in your kitchen.

The Glycemic Index is a scientific way of figuring out how a specific food raises your blood sugar, ranking foods on a scale of 0 to 100. Simple right? Well…the interpretation of what you should eat as a result of this measurement is where the grey shades come in.

Myth 1: Watermelon is high glycemic so therefore is bad for you. The answer to this is yes and no. Yes watermelon has a high glycemic index of 72, but there’s more to this story. The glycemic index measures a set amount of carbohydrates, 50 grams. This would equate to around 4 to 5 cups of watermelon, which you likely wouldn’t eat. Now introduce the Glycemic load, which measures the glycemic index to the amount of food you’re eating and rates it on a scale of 0 to 20. So one cup of watermelon (a reasonable amount to eat) ends up with a glycemic load of 7 making it low glycemic. With the high nutrient content of watermelon you wouldn’t want to eliminate this from your diet for no reason!

Myth 2: All low glycemic foods are good for you. No, no and no. Low glycemic simply measures how quickly a food raises your blood sugar. There’s more to healthy eating than just that one concept. For example, Peanut M&M’s and many sodas are medium glycemic…this doesn’t mean it’s OK to eat or drink them all day long. Sugar still impacts health in other negative ways. Don’t throw out everything you know about healthy eating. Glycemic Index is just one piece of the puzzle.

Myth 3: You’ve seen different glycemic index values for the same food so one source must be wrong. Nope. The testing for glycemic index is not an easy task. Typically, 10 different individuals are tested using the same amount of food on each. Then, their blood sugar is observed over a two-hour period to develop a blood sugar response curve. This response is then compared to a test food such as table sugar. The responses for each test are averaged giving the glycemic index of that food. Each person may have a small variation in her response to food, so if two separate labs tested the same food with different individuals you’ll see slight differences. Even the same food, say something like long grain rice, can vary slightly simply from small differences in harvesting and regions where different batches are grown. Bottom line: the differences are so small it’s not going to matter: A high GI food will still end up a high GI food.

Myth 4: All low glycemic foods are high in fiber. This is true most of the time, but not always. Overall, fiber helps to slow digestion and may be a factor in a food being low glycemic, but this is an overgeneralized statement. For example, a baked Russet potato is high in fiber but has a high glycemic load. Some brands of white enriched bread aren’t high in fiber, yet have a low glycemic load. A distinction such as this one is important for someone with diabetes who may be more sensitive to the rise in blood sugar. Finding foods that are both low glycemic and high in fiber is the way to go!

Moral of the story? Research developments are giving more insight into how a low glycemic diet affects your health. If you choose mostly low glycemic foods you can get better glucose control, feel more satisfied, improve heart health, decrease risk of stroke and even control food cravings. Just watch out for those generalized statements and broad assumptions.

Meri Raffetto is a Registered Dietitian, author of the Glycemic Index Diet for Dummies® and coauthor of Glycemic Index Cookbook for Dummies®, Mediterranean Diet Cookbook for Dummies®, Restaurant Calorie Counter for Dummies®, and Calorie Counter Journal for Dummies®. To learn more about Meri visit her blog.