5 Things to Know About Glycemic Index

Trinh Le, MPH, RD
by Trinh Le, MPH, RD
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5 Things to Know About Glycemic Index

While many carb-conscious eaters default to tracking their daily grams of carbohydrates, another popular way to keep tabs on carbs is by using the glycemic index (GI). Whereas carbohydrate counts measure the amount of this nutrient, GI measures the carbohydrate quality of foods.

What Is the Glycemic Index (GI)?

The Glycemic Index was invented in the 1980s to help people with diabetes manage their blood sugar levels. This scoring system ranks foods and drinks by assigning them a GI score. The GI score indicates how a person’s blood glucose will respond to eating a fixed amount of that food alone on an empty stomach. Foods with higher GI scores cause a sharper, more immediate rise in blood glucose after eating. Pure glucose (a simple sugar) is the standard reference, and scores 100 on the index—all foods are ranked from 0 to 100.

In carbohydrate-rich foods, a high GI food is usually starchier, more sugary and refined, while a low GI food is more fibrous. With higher GI foods, the carbs are easily broken down into glucose and quickly absorbed into the bloodstream, leading to an increase in blood sugar. Fiber in foods slows down this process, but fat and protein can, too, and are the reason why ice cream is considered a “low GI” food despite being relatively high in sugar and low in fiber. High-protein foods (meat, eggs and fish) or high-fat foods (oil, butter, mayonnaise) have so few carbs they score 0 on the index.

Here’s a brief run-through of the different GI levels of common foods:

Glycemic Index Level of Common Foods

Glycemic Index LevelFood Examples

Low GI
(less than 55)
Pasta, beans, fruits, dairy products (think milk, yogurt, cheese, ice cream), nuts and seeds, non-starchy vegetables, meats, oils
Moderate GI
(56 to 69)
Whole grains (think brown rice, oats, whole-wheat goods), corn, soda, sugar, honey, agave nectar, higher-sugar fruits (mango, grapes)
High GI
(70 or more)
Refined grains (think white rice, bread, instant oatmeal), boiled potatoes, melons, crackers

Interested in learning more? You can search for the GI scores for particular foods through the University of Sydney.

5 Downsides of Glycemic Index

While the glycemic index can be used as a tool to judge carbohydrate quality, it does have a few drawbacks, particularly if you’re using it as a means of controlling your blood sugar.

1. Quality is important, but so is quantity. The GI measures carbohydrate quality by ranking foods based on its effect on blood sugar, but it doesn’t take into account how much of it is eaten. Because of this, a new measure, called “glycemic load” (GL), was developed to account for both quantity and quality. While the glycemic load is more accurate compared to GI, it makes calculations a bit more complicated! Here’s the formula for GL:

     Glycemic Load = [Glycemic Index x Amount Carbs Eaten (in grams)] / 100

2. We rarely eat food in isolation. Think about any large meal you ate. Chances are many different foods were represented, and this is how it should be since a varied diet is a cornerstone of healthy eating. Both GI and GL give you a score for foods in isolation. For example, drinking a cola might rapidly spike your blood sugar, but if you drink it with a burger (a mixed meal of carbs, protein and fat), the effect is less pronounced.

3. Not all “low” GI foods are healthy. Adding fat will lower a food’s GI score, so ice cream, cheesecake, doughnuts and other high-fat but sugary desserts will have a low GI score. By frying a boiled potato with a GI score of 96, you can lower its GI score to 70. Does this mean these foods are healthier for you? Of course not! While you shouldn’t be afraid of fat, eating a calorie-dense, high-fat/high-carb diet is not helpful for weight loss.

4. GI & GL ignore fructose. Take a careful look at the table above—does anything surprise you? Pure table sugar, honey and agave nectar are considered “moderate” GI foods even though they are huge contributors to the added sugars we consume. Fructose, because of the way it’s metabolized, can be more detrimental to our health, but neither GI nor GL take fructose into account since it doesn’t cause a direct spike in blood sugar.

5. It makes eating more complicated. As you can see, carefully considering GI or calculating GL makes eating complicated. No matter how healthy an eating strategy is, it won’t be helpful to you it’s not simple and practical.

Using the GI for Weight Loss

Although the GI was originally designed for blood sugar control, this concept caught on in the weight loss world, and became the basis for popular diets like the South Beach Diet and the Zone Diet. Eating mainly low GI foods for weight loss follows the same logic as lower-carbohydrate diets: it should help prevent wild fluctuations in blood sugar and insulin. This idea is based on the fact that insulin helps with fat storage—thus having less of it around could help you store less fat.

The evidence is still lacking for using GI in weight loss, with a 2011 review showing no significant trends for low GI/GL diets and losing weight. Similar muddied evidence links low GI diets to reduced risk for diabetes, cancer and heart disease. Better science exists for following a low GL diet for weight loss, which makes sense since GL takes into account both carb quality and quantity.

It’s important to remember that both glycemic index and glycemic load focus on carbohydrates only—you’ll still need to make smart protein and fat choices for a healthy lifestyle. Instead of focusing on the numbers on these indexes, follow these simple tips (that you probably already know):

  • Get most of your carbohydrates from minimally processed whole grains, nuts and seeds, beans, fruits and non-starchy vegetables.
  • Eat processed grains (think white bread, white rice), potatoes, sugary drinks and sugary desserts only occasionally, and in moderation.
  • Balance your meal by eating high GI foods along with low GI foods.

Do you use GI/GL to help you eat healthier? If so, share your tips and tricks in the comments below.

About the Author

Trinh Le, MPH, RD
Trinh Le, MPH, RD
Trinh is a registered dietitian by day, blogger at Fearless Food RD by night. She loves helping folks develop a better relationship with food, which includes lots of cooking, eating and learning about nutrition. When she’s not snapping mouthwatering shots of (mostly) healthy food, you can find Trinh HIIT-ing it at her local gym. For more, connect with her on FacebookInstagram and Pinterest.