Glycemic Index: How to Use It to Support a Healthy Diet

You’ve probably heard the term "glycemic index" (GI), but may not understand exactly what it is or how to use it to support a nutritious diet and improve your health. The glycemic index is a critical measure in nutrition that assesses how quickly consumed carbohydrates affect blood sugar levels. Understanding GI can guide healthier food choices, particularly for managing diabetes and promoting overall well-being.

What Is the Glycemic Index?

The glycemic index is a ranking system based on how fast a carbohydrate-rich food increases your blood sugar after eating it. When you consume carbohydrates, your body breaks them down into a sugar called glucose, which then enters the bloodstream. Blood glucose rises at different speeds depending on the types of carbohydrates we eat. 

The GI scale ranks carbohydrate-rich foods from 0 to 100 based on how quickly they raise blood sugar after consumption. Foods with a higher score on the GI scale raise blood sugar faster than foods with a low score. 

The GI scale uses the following classifications: 

• Low-GI foods range from 0-55 
• Medium-GI foods range between 56-69
• High-GI foods range between 70-100

Foods are classified according to their glycemic response based on a standard food: white bread. This allows scientists to consolidate results on a wide variety of foods from multiple different studies. The University of Sydney in Australia holds a searchable database of carbohydrate-rich foods and their GI number.

The glycemic index is key for diabetes prevention and management. Additionally, knowing the glycemic index of the foods you eat can help you make choices that lower your risk of disease and chronic health problems. 

The American Heart Association states that foods with added sugars (higher GI foods) can increase the risk of cardiovascular and metabolic diseases. On the other hand, a diet full of complex carbs and fiber (lower GI foods) benefits gut health, which can support the immune system, brain health, metabolism, and more. Therefore, understanding the glycemic index and using it to guide your eating habits are key to maintaining good health. 

Low-GI vs. High-GI Foods

Aside from searching the GI database, how can you tell which foods have a high or low GI? The glycemic index of most foods cannot be found on the food label, though some packaged foods may have a low glycemic label. Even without a label, you can get a good idea of whether a food has a high or low GI by looking at its ingredients, added sugar, and fiber content. 

High-GI foods include most “simple” carbs that contain little, if any, fiber and can be broken down easily. They cause a rapid spike in blood sugar shortly after consumption. Some of these foods include but are not limited to:  

• white bread
• white rice 
• most cereals 
• potatoes 
• chips 
• processed pastries
• foods and beverages with added sugar 

Eating too many of these foods may increase the risk of diabetes, obesity, infertility, cancer, and cardiovascular disease. 

Medium-GI foods include fruits like bananas, pineapples, cherries, and raisins. Substitutes for white bread, including whole-wheat and multigrain, also tend to have a medium glycemic index. 

Low-GI foods include dairy products (without added sugars) and “complex” carbs like legumes and pasta. Other low-GI foods include brown rice and leafy greens. Meat and fish are not included in this index, as they do not contain carbohydrates.

Many factors affect a food’s glycemic index. When refined, grains are largely stripped of their natural fiber, resulting in a higher GI. Ripeness also affects a fruit’s glycemic index. The riper the fruit or vegetable, the higher the GI. Foods with a higher fiber, fat, or acid content tend to have a lower glycemic index, as these components slow the digestion of food.

What Is a Low-Glycemic Diet?

A low-glycemic diet emphasizes eating foods that score low on the glycemic index. This eating pattern involves avoiding processed foods, most potatoes and bread, crackers, chips, and products with added sugars. Small amounts of medium GI foods can also be consumed on a low glycemic diet.

The low-glycemic diet offers numerous health benefits, including decreased risk of type 2 diabetes and heart disease, prolonged satiety, and support for weight loss or maintenance. A 2019 review of studies found people with diabetes on a low-GI diet experienced reductions in body mass index (BMI), total cholesterol, LDL “bad” cholesterol, and hemoglobin A1c (a measure of blood sugar over time) levels. 

For people without diabetes, adopting a low-GI diet may support weight management and reduce the risk of cardiovascular diseases and hypertension. These benefits extend to healthy individuals by improving post-meal glucose and lipid metabolism. Other potential advantages of the low-GI diet include enhanced fertility and mood.

How to Lower the Glycemic Index of Foods

You can lower the glycemic index of your favorite foods by altering the way you prepare them or what you eat them with. The best way to reduce the GI of a food is to eat it along with fat and protein. Fat and protein both slow digestion, lowering the GI. For example, next time you make dinner, try swapping half of your high-GI starch with protein and fiber-rich legumes like beans or lentils. 

Changing the order in which you eat your meal can also affect GI. When consuming a meal with high-GI starch, eat your vegetables first, then your protein, followed by the carbohydrates. Consuming the carbohydrate portion of your meal last helps regulate your blood sugar. Try to emphasize whole, unprocessed foods in your diet, which tend to be lower GI than processed or liquid versions. 

Cooking time is another key way to lower the GI of your foods. Recent research indicates that longer cooking times elevate the glycemic response (GR) by speeding digestion. Shorter cooking times, such as cooking pasta al dente, result in a more gradual increase in glucose levels. 

Temperature and storage duration of starchy foods can also alter their molecular structure, significantly impacting blood sugar levels. When a starch is cooled after cooking, a process called retrogradation occurs. This causes the starch granules to shrink and reorganize into a crystalline form called resistant starch type 3 (RS3). This type of starch is more complex to digest, which, in turn, lowers the GI of the food.

Making healthy swaps for higher glycemic favorites in your pantry is easy! Instead of using white flour for your baked goods, try coconut flour. Not only is it gluten-free, but coconut flour is more nutrient-dense than regular flour, with a high fiber content and plenty of fats, resulting in a lower glycemic index. If you cannot eat coconuts, cassava flour is another good alternative. And instead of topping your salad with a heavy, cream-based dressing, try one with vinegar to help lower GI.

Glycemic Index vs. Glycemic Load

Glycemic load (GL) takes the glycemic index a step further. The glycemic index is based on a 0 to 100 scale of how quickly a carbohydrate-rich food raises blood sugar. The glycemic load multiplies the total carbohydrates in a food with its numerical GI score, divided by 100. 

Glycemic load values are classified as follows: 

• Low glycemic load foods: 10 or lower 
• Medium glycemic load foods: between 11 to 19
• High glycemic load foods: 20 or above

For example, according to the University of Sydney GI scale, an apple’s glycemic index is 39 with an average of 25 grams of total carbohydrates. Using the glycemic load equation, an apple’s GL is 9.75, which is considered low. 

Generally, foods with a low GI also have a low GL—but there are exceptions. For instance, watermelon has a high GI of 72 because its carbohydrates are quickly converted to glucose. However, due to its high water content and low overall carbohydrate amount, watermelon’s GL is only 4.4. In summary, glycemic load offers a clearer picture of the glycemic impact of a food’s average portion size.

Final Thoughts

The glycemic index is an important measure of how carbohydrates affect your blood glucose—but it isn’t the only tool for health prevention and blood sugar management. Along with high glycemic foods, stress, illness, dehydration, lack of exercise, and other factors may all increase your blood sugar. 

Maintaining a low-glycemic diet rich in whole foods incorporating healthy fats, proteins, and complex carbohydrates will help your blood sugar remain steady and may lower your risk for chronic health conditions like type 2 diabetes, heart disease, and high blood pressure. Good sleep and daily exercise also help naturally maintain healthy glucose levels. 

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