What is the Glycemic Index and Why Should You Care?

What Is Glycemic Index and How to Use It

If you’re like most people, chances are you’ve tried numerous diets that didn’t work or were challenging to stick with long-term. If so, you’re not alone. It’s far more effective and beneficial to your health to have an eating pattern that supports your healthy lifestyle. But what does a healthy eating pattern look like?

Fortunately, there are tools available that can help you tell which foods might not be the best for your health. One such tool is the glycemic index (GI). Take a look to see if GI could help guide your food decisions in the right direction.

The Glycemic Index and Carbohydrates

To understand GI, you’ll need to understand carbohydrates first. The carbohydrate is one of the three macronutrients for your body; the other two are protein and fat. But the good old carb takes the cake when we’re talking about the glycemic index (pun intended).

A macronutrient is a substance your body needs in large quantities to keep you healthy. Carbohydrates exist as sugar, fiber, and starch in your food, and have historically been a primary energy source for humans. Every carbohydrate is a long chain of glucose (sugar) molecules linked together.

As soon as a carbohydrate hits your mouth, your body begins working to digest it. As the carbohydrate passes through your digestive tract, countless enzymatic and chemical reactions go to work to break the sugars and starches down into glucose, fructose, and galactose. Meanwhile, the fiber in your meal passes through your body undigested, helping to keep your large intestine happy. The smaller molecules enter your bloodstream and get transported throughout your body to be used as energy or stored for later.

All Carbs Aren’t Not Created Equal

Unfortunately, not all carbs get processed in the same way, which makes sense if you think about it. Complex carbs (such as whole grains) take more effort to digest, whereas simple carbs (like white rice) take less effort.

The way your body digests carbohydrates directly correlates to the impact different foods have on your blood sugar. For example, if you eat white rice, it will have a greater impact on your blood sugar than if you eat wild rice; it is easier for your body to digest the carbs in the white rice and make them accessible for energy. Your blood sugar will go up more quickly.

All carbs impact your blood sugar, but some affect it more than others. The concept of the glycemic index can come in handy to help you determine which carbohydrates cause a spike in your blood sugar; something you want to avoid if you want to lose excess fat.

What is the Glycemic Index?

A glycemic index is a tool to help you determine how a specific food will impact your blood sugar. Only foods that include carbs are included in the index because some foods don’t impact your blood sugar in the same way (think butter or filet mignon).

Foods you digest quickly like white rice will rank higher on the index, while others will rank lower. The glycemic index for white rice is 72, while the glycemic index for wild rice is 45.

Foods that are high in protein, fiber, and fat rank lower on the glycemic index if you compare them to higher GI foods. For example, kidney beans, a good source of protein and fiber, have a GI score of approximately 24.

Glycemic Index Calculations

To score a food using the GI, scientists study the impact that specific food has on a person’s blood sugar by giving them a quantity of the food that contains 50 grams of carbohydrate (not including fiber). The person being studied is fasting so that no other foods impact the results, and their blood sugar is monitored for two hours after eating the food. 

Low GI food score at 55 or less

The scientists see what impact the food has on blood sugar and then assign it a GI score from 0 to 100. Pure glucose is the comparison for the scoring as it has the highest possible GI score of 100 based on that. According to Harvard Medical School, the scoring is as follows:

  • Low GI foods score at 55 or less. Examples include apples, green beans, oat bran, and non-starchy veggies.
  • Moderate GI foods score between 56 and 69. Examples include under-ripe bananas, green peas, yam, couscous, and macaroni.
  • High GI foods score at 70 or higher. These include some cold cereals, watermelon, potatoes, most bread, and candy.

Current glycemic index lists are pretty extensive, but they’re not exhaustive. You can still use them to get an idea of what other similar foods might score.

Limitations of the Glycemic Index System

A number of variables can impact the GI of a food. An under-ripe banana has a GI of 30 while a ripe one scores at 62! And how you cook food can also affect its score. 

Take the lovely potato as an example. Baked potato wedges have a GI of 54 while mashed potatoes have a GI of 83; it’s the same vegetable, prepared differently. 

Glycemic index charts and databases do account for some of these differences but not all. Also, the testing method for establishing a food’s GI isn’t realistic. Think about your last meal; you probably had a combination of food items, whether you ate a salad topped with nuts and dressing, or had some peanut butter on apple slices. 

Testing a food’s GI on an empty stomach is necessary to find the blood sugar impact of that specific food, but it also means you shouldn’t consider GI an exact science when you apply it to your daily eating habits. The testing method requires the subject to eat 50 grams of the food’s carbohydrate, which also brings up some challenges. Again, this doesn’t represent reality.

 As Esther Ellis, MS, RDN, LDN from the Academy of Nutrition and Dietetics succinctly puts it,“A serving of 50 grams of carbohydrate in one sitting may be reasonable for food such as rice, which has 53 grams of carbs per cup. But for beets, a GI ranking of 64 is a little misleading since beets have just 13 grams of carbs per cup; we would need to consume nearly 4 cups of beets in order to cause that spike in blood sugar levels.”

Glycemic Index may not be the most effective way for you to discover how a food will affect blood sugar at that moment. For example, if you only looked at the GI of raw pineapple, you might think it’s a food you’d want to be cautious of since it has a moderately-high GI of 58. But, a half-inch-thick slice contains about 7 grams of carbohydrate, which means a few slices probably won’t spike your blood sugar. In situations like the pineapple, the Glycemic Load (GL) can come in handy.

What is Glycemic Load?

Glycemic Load is a correction tool that gives you a more realistic picture of how food will influence your blood sugar. The formula looks like this:

Glycemic Load (GL) = (GI/100) x (net grams of planned carbohydrate)

GL = (GI/100) x (net grams of planned carbohydrate)

This calculation is a combination of portion size and glycemic index to give you a clearer picture of how the food will impact your blood sugar. It accounts for the specific amount of carbohydrate you anticipate eating from that food item.

Glycemic Load in Action

Let’s say you’re having four small strawberries (each strawberry has 0.5 grams of carbohydrate, so you’re having a total of two grams carbohydrate). The GI for strawberries is 40. To find the GL, divide 40 by 100 and multiply that by two to get a GL of 0.8. This GL score means these four strawberries have a low glycemic load, as the scoring is slightly different than that of GI:

  • Low GL foods have a score of 10 or less.
  • Moderate GL foods have a score between 11 and 19.
  • High GL foods have a score greater than 20.

Can You Benefit from Using the Glycemic Index?

Whether you’re already on the path to a healthier lifestyle, or you want to learn a bit more about the carb content of your food, the GI can strengthen your knowledge and help you choose foods that will support your health goals.

Glycemic Index and Chronic Disease

This system has the potential to help reduce your risk for chronic diseases since it typically promotes less-processed food choices, and research consistently shows eating a lot of processed foods is linked with weight gain. But, the research is still unclear if following a low GI diet can improve your health. 

The evidence is inconclusive; some studies show a low GI diet can improve multiple health markers, like your blood pressure and insulin sensitivity, and other studies say this may not be the case. Despite the mixed evidence, the GI system provides information you’ll find valuable. 

For example, if you’re not sure which foods are high in carbohydrates, look up the GI of different foods, it can help you learn quickly.

Diabetes and Glycemic Index

You should avoid highly processed foods whether or not you have diabetes; they drive your blood sugar through the roof and are detrimental to your health unless you eat them in moderation. If you have diabetes, your body doesn’t process sugar efficiently. If you eat large amounts of high-GI foods, it can be risky, and possibly cause hyperglycemia.

You can use the GI to gain a deeper understanding of the carb content of foods you typically eat. But for the purposes of managing your blood sugar, it may be simpler to directly count the carbohydrates in your meals. Basic carb counting is a tried-and-true method for monitoring changes in your blood sugar, so you might want to stick with the status quo.

How to Incorporate GI and GL Into a Healthy Lifestyle

To use GI and GL daily: 

  1. Begin by assessing the foods you typically consume. If oatmeal is one of your staples, familiarize yourself with its GI information by using a glycemic index list or database
  2. To balance your blood sugar, aim to eat foods that are low to moderate on the glycemic index.
  3. Pair high-GI foods with healthy proteins, fats, and fiber. For example, eat mashed potatoes (GI 83) with boiled carrots (GI 39) and roasted turkey. The pairing method will slow your body’s digestion of all the carbohydrates in your meal. You can also easily swap out high-GI foods for low-GI ones: 

High-GI foodLow-GI alternatives
CheeriosOatmeal (not instant)
Over-ripe bananasApples, Raspberries, Strawberries
RiceWild Rice
Corn FlakesOat Bran
French FriesSweet Potato Fries

Your Takeaways

You can use a glycemic index to gain a solid knowledge-base of the carbohydrate content of your food. The GI will help you avoid processed foods, encourage you to eat more whole-foods-based, and help you develop a balanced eating pattern. Remember, food isn’t the only factor in your healthy lifestyle; exercise, sleep, and reducing your stress are also essential. Be sure to talk with your healthcare provider about incorporating the glycemic index into your lifestyle, especially if you have a pre-existing condition like diabetes.

Author's bio

Grace Engels, RD

Grace Engels, RD

Grace Engels is a Registered Dietitian Nutritionist based in the Greater NYC Area. She completed her undergraduate coursework and requirements to sit for the RDN exam (including 1400 hours of supervised practice) at Cornell University. Grace keeps busy with three main jobs: Clinical ...