Monitoring your blood sugar levels is an excellent way to optimize your health and well-being. However, some of these metrics are challenging to understand. But by considering the glycemic index and glycemic load, you get a clearer picture of how a typical serving of food will affect your blood sugar levels.

When your body processes glucose, your insulin levels increase to help deliver glucose to your cells, bringing your blood sugar back to normal. If there’s too much glucose, your pancreas produces more insulin, which then converts the excess sugar into fat for storage. Calculating our glycemic index is a helpful way to begin to understand sugar’s effect on our body.

Glycemic Index

The glycemic index (GI) helps us understand how different foods affect our blood sugar levels. It measures how 50 grams of carbs from a specific food can raise your blood sugar. Foods with higher GI scores (from 1 to 100) cause your blood sugar to spike quickly, which is something you want to avoid. Consistent blood sugar levels are better for your overall health. While your brain and body need glucose to function, getting too much too quickly isn’t good for you.

To keep your blood sugar levels steady, focus on eating more low GI foods, which score between 0 and 55 on the glycemic index. Examples include nuts, most vegetables, whole oats, and certain fruits.

You can also enjoy medium GI foods, scoring between 56 and 70, like rice, whole wheat bread, and most fruits. High GI foods, scoring over 71, such as white bread and potatoes, should be eaten sparingly since they can cause rapid blood sugar spikes.

Eating foods that quickly raise your blood sugar levels can lead to more fat storage in your body. The glycemic index helps you choose foods that promote steady blood sugar levels and healthier eating habits.

Glycemic Load

While the GI measures how quickly 50 grams of carbohydrates from a food can raise your blood sugar, the GL goes further by considering the actual amount of carbohydrates in a typical serving of that food.

The GL is calculated by taking the food’s GI, multiplying it by the carbohydrate content (in grams), and then dividing by 100. For a comprehensive list of foods glycemic index values and their glycemic loads, we recommend you refer to the Harvard Medical School Index.

1. Identify the Glycemic Index (GI) of the food, as indicated on a GI chart like this one:

   • For watermelon, the GI is 72.

2. Determine the amount of carbohydrates in a typical serving:

   • One cup of watermelon (154 grams) contains about 11.6 grams of carbohydrates.

3. Use the formula to calculate the Glycemic Load (GL):

   • The formula is: GL = (GI × Carbohydrate content per serving) / 100

   • For watermelon: GL=(72×11.6 grams) / 100

   • The glycemic load of one cup of watermelon is 8.35

The glycemic load is often more reliable than the glycemic index alone. For example, watermelon has a high GI of 72, meaning it can raise blood sugar levels quickly. However, watermelon is mostly water, and a typical serving has a very low carbohydrate content.

Therefore, the GL of a serving of watermelon is only 8.35, which is very low. While watermelon can cause a quick rise in blood sugar, it won’t keep levels elevated for long due to its low carbohydrate content.

To put it in perspective, the GI measures the effect of a standard 50-gram serving of carbohydrates from a food. Eating 50 grams of carbohydrates from watermelon would be unrealistic for most people. One cup of watermelon (about 154 grams) contains approximately 11.6 grams of carbohydrates. You would need to eat over four cups of watermelon to consume 50 grams of carbohydrates.

Putting the Glycemic Load into practice

Here are a few helpful tips to navigate Glycemic Load targets.

When using the glycemic load as a reference for your food, keep in mind that foods between 10 and 15 on the glycemic load are considered moderate.

These moderate GL foods will not keep your blood glucose levels elevated for long periods of time.

However, foods with a glycemic load higher than 15 should be eaten sporadically, as they will spike blood sugar levels and keep them elevated for longer.

Having rapid spikes and consequential decreases will then will cause you to feel unsatiated and fatigued, so be sure to eat these items with protein to even out the spike.

A word of caution: while understanding the glycemic load is important, every person reacts differently to foods, even among very healthy people. For instance, you — an active, individual who eats lots of fresh produce — might have a glucose spike from a cup of watermelon, but your more sedentary friend may not.

The more your glucose levels spike, the higher your chances are of chronic inflammation. The best way to see how your body reacts is to wear a glucose monitor. If you or your members of your family have health-related issues involving blood sugars, talk to your doctor to see if glucose monitoring is appropriate for you.

How is fructose involved?

If you’re wondering how fructose fits into this index, we hear you! It can be hard to talk about glucose without mentioning fructose—take a look at our sugar article.

Unlike glucose, fructose is considered to be a low GI food. With a glycemic index of 19, fructose causes significantly less insulin secretion than glucose. Naturally-occurring fructose is actually ranked lowest on the GI scale of all natural sugars.

High levels of fructose in your body, however, can cause cellular damage— in fact, excess fructose in your body causes seven times more cell damage than excess glucose. This is another reason why you have to be careful when judging foods solely by their glycemic index.

How can I quickly calculate glycemic loads at the grocery store?

Finding the glycemic index (GI) of foods while shopping at the grocery store can be a bit challenging, as GI values are not typically listed on food packaging. However, there are several strategies you can use to access this information:

• Smartphone Apps: There are many apps available that provide GI values for various foods. Apps like “MyFitnessPal,” “Glycemic Index Load,” and “Fooducate” can be very helpful.

• Printed Guides and Books: Some people find it useful to carry a small printed guide or book that lists the GI values of common foods. There are several comprehensive guides available in bookstores or online.

• Online Databases: Before going to the store, you can look up the GI values of foods on websites such as the Glycemic Index Foundation (glycemicindex.com) or other nutrition-focused sites, like Dirt to Dinner in the infographic above!

• Nutrition Labels: While the GI value might not be listed, you can get a sense of a food’s impact on blood sugar by checking the carbohydrate content and the presence of sugars and dietary fiber. Foods high in fiber and low in sugars generally have a lower GI.

• Healthy Eating Lists: You can refer to general lists of low GI foods, such as whole grains, legumes, most vegetables, nuts, and certain fruits. These lists can guide your shopping choices.

By using these resources, you can make more informed decisions about the GI of foods and better manage your blood sugar levels.