What Is the Glycemic Index?

The glycemic index (GI) is a number that helps show how quickly carbohydrate-containing foods raise your blood sugar. Foods are scored from 0 to 100, with higher numbers indicating a faster rise. For example, white bread and sugary drinks have a high GI, while lentils and nuts have a low GI.

What About Glycemic Load?

The glycemic load (GL) takes the GI and the portion size into account. It’s calculated by multiplying a food’s GI by the amount of carbohydrate in a serving, then dividing by 100.

For example, if a food has a GI of 70 and a serving contains 15 grams of carbohydrate, the GL would be 10.5 (70 × 15 ÷ 100). GL gives a clearer picture of how a realistic serving of food will affect blood sugar compared to GI alone.

Benefits of Using GI and GL

GI and GL can be useful tools, especially for people with diabetes or others concerned with blood sugar control. Choosing foods with a lower GI or GL may help reduce spikes in blood sugar and, in some studies, has shown modest improvements in long-term blood sugar measures like A1C.

These tools can also help people see that not all carbohydrates behave the same way. A bowl of beans will affect your blood sugar differently than a slice of white bread, even if both have the same number of carbs.

Shortcomings of GI and GL

While helpful, GI and GL are not perfect systems. Several factors can change how your body responds to a food:

• Meal context: Fat, protein, and fiber slow digestion and can reduce blood sugar spikes.
• Preparation: Cooking methods, ripeness, temperature, and brand can all alter a food’s GI.
• Individual factors: Your gut health, genetics, and insulin sensitivity all play a role.
• Nutritional quality: A food with a lower GI is not automatically healthier — for example, chocolate has a lower GI than a baked potato, but that doesn’t mean it’s a better choice for everyday health.

Research also shows mixed results: some studies find benefits from using GI/GL to guide food choices, while others show little difference. For this reason, the American Diabetes Association (ADA, 2024) states that GI and GL can be considered as optional tools, but the focus should remain on the overall quality of carbohydrates and dietary patterns.

What to Focus on Instead

According to current guidelines, the bigger priorities for blood sugar and overall health are:

• Choose high-fiber, minimally processed carbs: vegetables, fruits, legumes, whole grains, and dairy.
• Limit added sugars and refined grains, especially sugary drinks.
• Pay attention to portion sizes and consistency.
• If you use insulin, remember that fat and protein can cause delayed rises in blood sugar and may affect your dosing needs.

The Bottom Line

The glycemic index and glycemic load can provide insight into how foods affect blood sugar, but they are just one part of the picture. They should not be the main guide for choosing what to eat. Instead, focus on the quality of your carbohydrates, aim for balanced meals, and make adjustments based on your own blood sugar responses.