Difference Between Glycemic Load and Glycemic Index

The glycemic index (GI) and glycemic load (GL) refer to ways of measuring how certain foods might affect your blood sugar.

GI and GL were originally developed to determine which foods were best for people with diabetes, but whether you're diabetic or not, these tools are useful for blood sugar management and better diet planning.

This article will explore the similarities and differences between GI and GL and how your glycemic response influences your health and well-being.

What Is Glycemic Index?

The glycemic index (GI) is a system of classification in which the glycemic responses of foods are indexed against a standard (white bread). It was introduced in 1981 by David Jenkins, MD, a scientist at the University of Toronto, to express how much dietary carbohydrates impact blood sugar (glucose) levels. 

GI is a numerical way of describing how carbohydrates in foods affect blood sugar levels. The GI ranges from 0 to 100, with pure glucose being given a value of 100.

Processed foods made with refined sugar and flour such as candy, bread, cake, and cookies have a high GI, while whole foods such as unrefined grains, non-starchy vegetables, and fruits tend to have a lower GI.

GI is categorized as follows:

• Low GI: 55 or less
• Medium GI: 56–69
• High GI: 70 or higher

What Is Glycemic Load?

The glycemic load (GL) is a relatively new way to assess the impact of carbohydrate consumption on the rise of blood sugar in the body. It gives a fuller picture than GI alone.

GL uses GI and the amount of total carbohydrates per serving of a specific food to estimate both how quickly a food causes blood sugar to rise and how much blood sugar levels will rise in total after eating.

By taking GI and the amount of carbohydrates per serving into account, GL highlights what nutritionists have known for a long time: High or low GI does not necessarily equate to healthy or unhealthy. Most fruits, for instance, have a high GI, but low GL.

How Glycemic Load and Glycemic Index Are Related

Your blood sugar levels are dependent on many factors, including insulin levels, how quickly sugar is absorbed into your bloodstream, and how much sugar (glucose) is in a meal per serving.

GI tells you something about how high your blood sugar could rise with certain foods, but it does not tell you how high your blood sugar will go when you actually eat the food. That’s where glycemic load comes into play. 

GL gives you a more accurate picture of how food impacts your blood sugar levels, considering the following factors:

• The types of sugar and starches in the food
• The way your food is prepared
• Fat content
• Fiber and carbohydrate content
• Serving size
• Rate of absorption and digestion of food products

GL provides food's real-life impact on your blood sugar. Watermelon, for example, has a high glycemic index (80), but its low carbohydrate content per serving results in a glycemic load of only 5.

How to Calculate Glycemic Load

GL is a great tool because you don’t need to be a math whiz to calculate it. Dietary GL is calculated by the amount of carbohydrate contained in a specified serving size of the food multiplied by the GI of that food and divided by 100. (Mathematically, GL = GI × available carbohydrate (g) /100)

GL is categorized as follows:

• High GL: 20 or higher
• Medium GL: 11–19
• Low GL:10 or less
  

Glycemic Response and Diet

GL and GI estimate the rise of blood glucose in the body after eating a specific food. Generally, foods with a low GL have a low GI, whereas foods with an intermediate or high GL can range from very low to very high GI. 

GI is a significant factor in GL. The lower a food's GI, the slower blood sugar rises after eating that food. In general, foods that are higher in carbs and contain more processed ingredients have a higher GI. On the other hand, foods high in fiber or fat have lower GIs.

GI alone does not tell the full story, because it doesn’t account for the many factors that impact your blood sugar. GL represents the quantity and quality of carbohydrates in the overall diet and their interactions in the body. This is why GL is widely regarded as a more reliable tool than the glycemic index alone.

Sample Low Glycemic Load Menu

Glycemic load offers information about how foods affect blood sugar and insulin. The lower a food's glycemic index or glycemic load, the less it affects blood sugar and insulin levels. 

Research shows that sticking to a low GL diet can play an important role in staving off type 2 diabetes and heart disease.

Here is a GL reference list with many common foods based on their GL reference range.

Foods with a low GL of 10 or less include:

• Hummus
• Green peas
• Carrots
• Black beans
• Lentils
• Fruits (watermelon, apples, oranges, pears)
• Microwave popcorn
• Nonfat milk

Foods with an intermediate GL of 11–19 include:

• Some cereals, like Special K
• Rice cakes
• Reduced-fat yogurt with fruit
• Banana, ripe
• Dates, dried
• Pasta

Foods with a high GL of 20 or more include:

• Instant oatmeal
• White rice
• Raisins
• Macaroni and cheese (commercially made, like Kraft)
• Baked russet potato
• Sweet potato
  

Glycemic Load and Disease Prevention

Observational studies have yielded mixed results regarding the association of GI, GL, and adverse medical events.

Studies show that carbohydrates are not bad in and of themselves. Rather, diets that are too high or too low in carbohydrates can be problematic. Eating carbohydrates in the form of whole foods, such as whole grains, legumes, fruits, and vegetables is better for your health than the carbohydrates contained in processed foods.

Overall, research shows that eating a low glycemic load diet, especially one that is high in fiber and whole-grain foods, is considered beneficial for cardiovascular disease prevention and several other chronic diseases, such as type 2 diabetes. 

One study, the PURE (Prospective Urban Rural Epidemiology) study, looked at how GI and GL impact cardiovascular health in nearly 140,000 people. The PURE study found that higher GI and GL are associated with a greater risk of adverse cardiovascular disease events in adults with established cardiovascular disease.

However, the study was limited by recall bias due to its observational study design. More follow-up studies are needed to verify these results.

Summary 

Glycemic index explains how carbohydrates may affect blood glucose levels, whereas glycemic load takes into consideration every component of the food as a whole, giving a more real-life picture of a food’s impact on your blood glucose levels. Both of these tools are valuable in blood sugar management and diet planning.