What is Glycemic Load and how is it different from Glycemic Index?
Glycemic Load (GL) is a measure that factors in the amount of carbohydrate in a portion of food and its impact on blood glucose levels. The glycemic load factors in both the quality as well as the quantity of the carbs you eat.
You may have heard of another measure called the Glycemic Index (GI). The glycemic index ranks foods based on how quickly a food causes our blood sugar levels to rise. It is a number or a value assigned to foods, based on how much they increase blood sugar levels. Foods are ranked on a scale of 0-100, with pure glucose (sugar) being assigned a value of 100. The lower a food’s GI, the slower blood sugar rises after eating that food. However, the glycemic index does not take portion sizes into account. For example, watermelon is classified as a high glycemic index food with a GI of 80. But a single portion of watermelon only has a glycemic load of 8.8 because of its low carbohydrate content. The glycemic load therefore corrects for the glycemic index by combining portion size and glycemic index into one number.
How is the Glycemic Load calculated?
The glycemic load is calculated by multiplying the carbohydrate content of the actual serving size of a food with that food’s GI and dividing the result by 100.
Glycemic Load Formula
GL = GI X Carbohydrate/ 100
In order to arrive at the glycemic load for a particular food you would need to know:
- The glycemic index of that food. You can find the glycemic indexes for different foods here
- The amount of carbohydrate present in that quantity of food
If we were to take the same example of watermelon above, we would calculate the GL for watermelon as follows:
- GI of watermelon = 80
- Amount of carbohydrate in a single serving of watermelon (one cup of diced watermelon, 152gm) = 11gm
- So the GL for a single serving of watermelon = 80 X 11/100 = 8.8
Why you should consider both the Glycemic Load and the Glycemic Index when evaluating foods
Let’s consider the same example of watermelon to understand why looking at the GI of a food in isolation may be misleading. We saw how while watermelon is classified as a high GI food, when you consider a single portion size, it is actually a low GL food. On the other hand, a doughnut has a GI of 76, lower than the GI of watermelon (80). So if you were to look at the GI alone you might arrive at the false conclusion that a doughnut is a better food choice. However, when you consider the GL you would find that a mid sized doughnut has a GL of 17 because it has 23gm of carbohydrate.
GL of a mid sized doughnut = GI X Carbohydrate/ 100 = 76 X 23/100 = 17
So while the GI is a useful tool to help make healthier food choices, it should be used with the GL to see how different sized portions of different foods compare with each other. This might help you to decide between a single portion of white rice (1 cup, GI 66, GL 35) and a portion of couscous (1 cup, GI 60, GL 27) to go with your main course of a chicken gravy, for example.
What counts as a high and low glycemic load?
The GL values of foods are classified into 3 categories as follows:
- Low GL foods: 10 or less
- Medium GL foods: Between 11 and 19
- High GL foods: Greater than 20
Foods with a low GL include peanuts (¼ cup of peanuts has a GL of 1), skim milk (8 oz has a GL of 4) and all bran cereal (1 cup has a GL of 9) to name a few. Foods with a medium GL include cooked oatmeal (1 cup has a GL of 11.7), bananas (1 large banana has a GL of 12.4) and boiled brown rice (1 cup has a GL of 18). Some examples of foods with a high GL are cornflakes (surprise, surprise! 1 cup has a GL of 21), candy bars (1 Snickers candy bar has a GL of 22.1), raisins (2 tablespoons has a GL of 27.3) and potatoes (1 medium baked potato has a GL of 23).
The Glycemic Index Foundation recommends keeping the daily glycemic load under 100 for optimal health.
How to use the Glycemic Load
The Glycemic Load is a useful tool to choose healthier foods and portion sizes. It can be particularly useful to assess the GL of a food you eat fairly often or even of a new food you plan to try. You can use it with the Glycemic Index to maintain good blood glucose levels. The glycemic load and glycemic index are particularly useful metrics for people who have diabetes as they help you evaluate the impact of the food you eat on your blood glucose levels, and plan your meals accordingly.
It is important to keep in mind that while the GI and GL are useful tools that can help you make better food choices, you cannot rely on them in isolation. They don’t factor in the nutritional content of different foods, for example. So a medium baked potato might have a higher GL than a Snickers candy bar, but is much better in terms of nutritional content. So while it is good to be aware of the GI and GL of the food you are eating, a focus on overall dietary content and quality is the best approach to maintaining optimal health.
Read More: What is the Glycemic Index?