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Making Sense of the Glycemic Index

Making Sense of the Glycemic Index

You may know the difference between simple and complex carbohydrates, but if you're trying to eat healthier and shed a few pounds, should you also consider the glycemic index?

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Whether you're trying to control or prevent diabetes, lose weight, or just maintain a healthy weight and lifestyle, chances are managing your carbohydrate intake is important to you. You may have already reduced the amount of cookies, candies, white bread, pasta and other refined (or simple) carbs in your diet in favor of more nutritious whole grains, fruits and vegetables. If that's the case, good for you! But should you also be paying more attention to the glycemic index of the foods you eat?

The glycemic index (GI) assigns a number to foods containing carbohydrates based on how much that food can raise your blood sugar. It's another way to make decisions about your diet based on the different ways carbohydrates act in your body. It's based on a scale of zero to 100, with zero representing a food with no carbohydrates (such as butter) and 100 being pure glucose. It was originally developed to help people with diabetes or pre-diabetes make better food choices, and today the results of multiple studies are maintained in a database called the Sydney University Glycemic Index Research Services. It’s important to note that not every food has been studied and assigned a GI, but the list is extensive and certainly covers the majority of foods consumed in the U.S.

When you consume something with carbohydrates, your body breaks down the sugar and starches into glucose – the primary source of energy for cells. Different types of carbohydrates behave differently based on how quickly they are digested and enter the bloodstream. The carbohydrates (sugar) in a can of soda will be broken down faster than an equal amount of carbohydrates from fiber-rich broccoli and whole grain bread. That means soda will cause an increase in your blood sugar levels, followed by a rapid drop to more normal levels in a healthy person. But over time, those spikes and dips can lead to insulin resistance and other health concerns.

The glycemic index ranks foods based on low, medium, and high GI values. The lower the value, the less impact it will have on raising blood sugar. Legumes, most vegetables, dairy, and nuts are all low glycemic foods, and won’t cause rapid fluctuations in blood sugar. On the other hand, foods with a high GI such as most processed foods, baked treats, fast food, and white bread can quickly raise your blood sugar and then leave you feeling tired and hungry soon after as it plummets back down. Foods with a medium GI ranking include many fruits, starchy vegetables, and whole grain breads. In general, foods with more fiber and fat will have a lower GI number. Search for GI numbers for various foods here.

But the glycemic index of a food doesn't really tell the whole story. It ignores other important nutritional considerations such as calories, fat, fiber, protein, and vitamin and minerals various foods may deliver. Many low GI foods could be lacking in nutrients, and medium or high GI foods could deliver a powerhouse of other nutritional benefits necessary for a balanced diet. That's why it's also important to consider the glycemic load of foods as well. The glycemic load (GL) measures both how quickly a certain food will convert to glucose and enter the bloodstream and how much glucose it can actually deliver. The GL is calculated by taking the grams of carbohydrate contained in a food, multiplying that by the GI index, and then dividing by 100. Foods with a number of 20 or higher are high GL, those between 11-19 are medium, and foods less than 10 or low GL. The example most often cited by nutritionists to illustrate the importance of the GL is watermelon. Watermelon is a high GI food with a value of 80, but a serving contains only about 7 grams of carbohydrate, so the GL is about 5.6 – making it a low GL food.

Understanding more about the glycemic index and glycemic load of various foods can certainly help you make better decisions for your health. For most people, it's probably not necessary to calculate the numbers for every food you eat. A balanced and varied diet will naturally contain an abundance of nutrient dense food, with minimal high GL foods that can really wreak havoc on your blood sugar. If you have diabetes or are concerned about blood sugar fluctuations or insulin resistance, talk to your doctor or a certified nutritionist about how a diet with lower GI and GL foods can help you better manage your health. And never make drastic changes to your diet without talking to your doctor first.


This article first appeared in the September 2022 edition of the HealthPerks newsletter.

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