Which is better: Glycemic Index or Glycemic Load?

According to the Linus Pauling Institute, the glycemic load is a more reliable tool than the glycemic index alone for predicting a food's impact on blood sugar levels. This article will demystify the key differences, helping you understand whether glycemic index or glycemic load is better suited for your dietary goals.

Quick Summary

The glycemic index ranks carbohydrates by how quickly they raise blood sugar, while the glycemic load provides a more practical measure by factoring in both the food's index and the portion size. Understanding both concepts can help you make more informed food choices for managing blood glucose levels effectively.

Key Points

• Glycemic Load is more comprehensive: While GI only measures how fast carbohydrates raise blood sugar, GL also includes the portion size, providing a more accurate picture.

• Watermelon fallacy: Watermelon has a high GI but a low GL due to its low carbohydrate density, demonstrating why GI alone can be misleading.

• Strategic food combinations: Combining high-GI foods with low-GI foods, protein, and fat can lower the overall glycemic load of a meal.

• Portion size matters most for GL: Even low-GI foods can have a high GL if consumed in large quantities, so being mindful of portion size is critical.

• GI still has its place: GI can be a useful quick reference for comparing similar foods, but should not be the sole determinant of food choices.

• Focus on whole foods: Prioritizing whole, unprocessed foods naturally helps manage both GI and GL for better blood sugar control.

• Both are valuable tools: For effective diabetes management or weight control, considering both GI and GL helps create a more balanced and informed eating plan.

Understanding the Glycemic Index (GI)

The glycemic index (GI) is a numerical ranking system for carbohydrate-containing foods based on how quickly they are digested and converted into glucose, or blood sugar. Foods are ranked on a scale from 0 to 100, with pure glucose serving as the reference food with a GI of 100. A high GI (70 or higher) indicates a food that causes a rapid spike in blood sugar, while a low GI (55 or less) indicates a food that produces a slower, more gradual rise. This system was originally developed to assist people with diabetes in managing their blood glucose.

How GI Values are Measured and Influenced

GI values are determined in a laboratory setting by feeding human volunteers a portion of a food containing 50 grams of available carbohydrates. Their blood glucose levels are then measured over a period of two hours. The area under the blood glucose curve for the test food is compared to the area under the curve for the reference food (glucose).

However, a food's GI can be influenced by several factors:

• Processing: Highly processed foods, like white bread, tend to have a higher GI than their whole-grain counterparts, like whole-grain bread.
• Cooking Method: The cooking time can affect the GI. For instance, al dente pasta has a lower GI than soft-cooked pasta, and a whole baked potato has a lower GI than mashed potatoes.
• Ripeness: The ripeness of a fruit impacts its GI. An unripe banana has a lower GI than a ripe one.
• Fat, Fiber, and Protein: The presence of fat, fiber, and protein in a meal slows down digestion, which can lower the overall glycemic response.

The Limitations of Glycemic Index

While GI provides a useful guideline, it has significant limitations that make it an imperfect tool for real-world application.

• Ignores Portion Size: GI is based on a fixed 50-gram carbohydrate portion, which is not realistic for many foods. For example, watermelon has a high GI, but a standard serving contains very few carbohydrates, meaning its real-world impact on blood sugar is minimal.
• Excludes Other Nutrients: GI focuses solely on carbohydrates and ignores the effects of fat and protein. The overall composition of a meal dramatically influences blood sugar response.
• Individual Variability: An individual's glycemic response to a particular food can vary day-to-day and is influenced by factors like genetics, metabolic status, and even the time of day.

Introducing the Glycemic Load (GL)

The glycemic load (GL) was developed to address the limitations of the GI by providing a more complete picture of a food's effect on blood sugar. GL accounts for both the quality of the carbohydrate (GI) and the quantity of the carbohydrates consumed in a realistic serving size.

The GL is calculated with the following formula: GL = (GI × grams of available carbohydrate per serving) / 100

This calculation provides a more practical and reliable measure of a food's overall impact on blood sugar. Foods are then categorized based on their GL:

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

An Example of GL in Action

Consider the earlier example of watermelon and white spaghetti, and let's compare them again to see why GL is a superior metric. Watermelon has a high GI (around 72) but a low carbohydrate density, resulting in a low GL (typically 8 for a one-cup serving). Conversely, al dente white spaghetti may have a moderate GI (around 46), but a typical portion contains a large amount of carbohydrates, pushing its GL into the high range (around 20). This shows that a moderate GI food, when consumed in a typical portion, can have a greater impact on blood sugar than a high GI food consumed in a typical portion. This is the critical piece of information that GI alone misses.

GI vs. GL: A Comparative Table

Feature	Glycemic Index (GI)	Glycemic Load (GL)
Measurement	Measures how quickly carbohydrates raise blood sugar.	Measures the total impact of a food on blood sugar.
:---	:---	:---
Considerations	Focuses only on carbohydrate quality.	Considers both carbohydrate quality (GI) and quantity (portion size).
Real-world Context	Less realistic; based on a standardized 50-gram carbohydrate portion.	More practical; based on typical, real-world serving sizes.
Calculation	A single value, no calculation needed by the consumer.	Requires a calculation: (GI x carbs) / 100.
Watermelon Example	High GI (72), potentially misleading.	Low GL (8), accurately reflects minimal impact.
Effectiveness	Good as a general guide, but limited accuracy in real meals.	More accurate for predicting blood sugar response in real meals.

How to Apply Both Glycemic Tools for a Balanced Diet

For most people, especially those with diabetes or insulin resistance, focusing on the glycemic load is the more practical and accurate approach. However, understanding both allows for better decision-making:

• Prioritize Low GL Foods: Build your diet around low-GL options, which include most vegetables, legumes, and whole grains.
• Be Mindful of Portion Sizes: For foods with a high GI but low carb count (like watermelon), you can enjoy them in moderation without significant blood sugar impact. For low GI foods that are high in carbs (like pasta), be mindful of portion sizes to keep the GL in check.
• Combine Foods Strategically: Pair high-GI foods with low-GI foods, proteins, and healthy fats. For example, adding chicken and cheese to pasta will lower the overall meal's glycemic response.
• Consider Other Factors: Remember that GL is one tool among many. Nutritional value, fiber content, and overall calories are also crucial for a healthy diet.

Conclusion: The Bottom Line

While the glycemic index is a foundational concept in nutrition, the glycemic load is the superior tool for practical dietary management. By incorporating portion size, GL offers a more realistic and accurate prediction of a food's overall impact on blood sugar. It empowers you to make smarter, more nuanced food choices that go beyond a simple high/low rating. For individuals managing their blood sugar, focusing on the glycemic load provides a clearer and more effective roadmap to health.

Sources:

• Better Health Channel: Carbohydrates and the glycaemic index
• Harvard Health Publishing: The lowdown on glycemic index and glycemic load
• Verywell Health: Glycemic Load vs. Index: Tools for Blood Sugar Control
• Linus Pauling Institute: Glycemic Index and Glycemic Load
• Diabetes Research and Clinical Practice: Glycemic index versus glycemic load – What does matter in life?

Frequently Asked Questions

What is the primary difference between glycemic index and glycemic load?

The glycemic index (GI) measures how quickly a carbohydrate raises blood sugar, while the glycemic load (GL) measures the total impact on blood sugar, taking into account both the GI and the amount of carbohydrate in a typical serving.

Is a low-GI food always healthy?

Not necessarily. Some low-GI foods, like chocolate, are low because of their high fat content, not their nutritional value. It's important to consider other factors like calories, vitamins, and minerals.

How do I calculate the glycemic load of a food?

To calculate the GL, you multiply the food's GI by the amount of available carbohydrates (in grams) in a serving, then divide that number by 100.

Can I still eat high-GI foods?

Yes. High-GI foods can be eaten in moderation, especially when combined with low-GI foods, protein, or healthy fats. This helps to slow down the overall release of glucose into the bloodstream.

Does cooking affect GI or GL?

Yes. The way food is cooked and processed can alter its GI. For instance, cooking starches longer can increase their GI, while adding fat or fiber can decrease it.

Which metric is more important for people with diabetes?

While both are useful, the glycemic load is generally considered a more practical and accurate tool for people with diabetes because it accounts for portion size, which is a major factor in blood sugar management.

How can I lower the glycemic load of my meals?

You can lower your meal's GL by focusing on smaller portions of high-carbohydrate foods, choosing low-GI carbohydrates, and combining them with protein, healthy fats, and fiber-rich vegetables.