Why Is Checking The Glycemic Index Of Food Not Enough?

Expert-reviewed by Ashwini S.Kanade, Registered Dietician and Certified Diabetes Educator with 17 years of experience

Your diet is one of the most important aspects of managing your diabetes. You may have doubts regarding what to eat and what not to eat. Your doctor will advise you to have foods with low ‘glycemic index’ and low ‘glycemic load’. But what do these terms mean? Here’s everything you need to know about them.

What is Glycemic Index?

Different foods contain different types of carbohydrates, which are broken down by the body into glucose over a period of time. The glycemic index (GI) measures how quickly the carbohydrates in a particular food item convert into glucose, thus raising the body’s blood sugar level.

Pure glucose, with a GI of 100, is the reference point with which other food items are compared and ranked on a scale of 0 to 100. Foods that are digested, absorbed and metabolised rapidly cause a dramatic, more immediate spike in blood sugar levels, and so have a high GI (closer to 100). Foods that contain slower-acting carbohydrates, which take longer to be processed by the body, have a lower GI.

Food items with a low GI are considered healthier because they produce smaller or more gradual increases in blood sugar level.

What is Glycemic Load?

While GI is measured based on the type of carbohydrate, glycemic load (GL) takes into account the amount of carbohydrate present in a portion of food. It helps assess how one typical serving of food affects blood sugar levels.

The GL of a food item is determined by multiplying a food’s glycemic index by the amount of carbohydrate in a serving of that food.

What is the difference between the two?

The glycemic index tells you only the type of carbohydrate in a typical serving of a food item, but not the total amount of carbohydrates in that serving. Hence it gives a measure of the quality of carbohydrate in your food, but not its quantity.

On the other hand, glycemic load considers the quantity of carbohydrate. It tells you how much carbohydrate is present in a particular serving of a food item.

Looking for diabetes-friendly recipes? Here are easy lunch recipes and some quick breakfast recipes to help you get started.

How are the glycemic index and glycemic load values of a food item interpreted?

Glycemic Index values are interpreted as:

• GI ≥ 70 – high
• GI 56 to 69 – medium
• GI ≤ 55 – low

Glycemic Load values are interpreted as:

• GL ≥  20 – high
• GL 11 to 19 — medium
• GL ≤ 10 – low

What does it mean when a food item has a high glycemic index but low glycemic load?

If a food item has a high GI, that means the carbohydrates present in it are converted to glucose more rapidly and cause a spike in blood sugar levels. But the GI does not tell you how much of the food needs to be consumed to cause that rapid spike.

There are some foods with a high GI that cause a drastic rise in blood sugar levels only when consumed in very large quantities, far more than what you would typically have in one serving. Watermelon, for instance, has a GI of 72, but a GL of only 4.^[1] This means you would have to eat an entire watermelon in one go for it to cause your blood sugar to spike.

Why does glycemic index not give you the full picture?

Your insulin response and blood sugar fluctuation are influenced by both: the type and amount of carbohydrates present in the food you consume.

GI tells you about the quality of food that you consume, not the portion size. It does not take into account how much you are actually consuming. So it cannot predict what effect the amount of food you eat (and the carbohydrates it contains) will have on your blood sugar level. Regardless of whether you consume 100 grams or 1,000 grams of food, the GI of a food item remains the same. This could be misleading.

For example, you may prefer to eat a food item with GI 50 instead of one with GI 100, thinking that it will have a lesser impact on your blood sugar. But it can cause the same rise in blood sugar as that of a food item with GI 100 if its portion size is twice that of the food with GI 100.

So, how should you choose what to eat?

What should you look out for when you choose a food item — its glycemic index or glycemic load? Is one of the two better than the other at determining whether a food item is suitable for a person with diabetes?

Foods that have a high GI cause greater spike in your blood sugar levels whereas low GI foods produce a smaller rise. Studies suggest that replacing high GI carbohydrates with low GI forms improves sugar control.^[2]

But food quantity matters too. Counting carbohydrates can help predict your blood sugar response better. This is where GL helps you. It is a better indicator of the impact of a food item on your blood sugar levels and gives you a fuller picture. A food item with higher GL will stimulate insulin and raise your blood glucose significantly. 

Though glycemic index can be very useful, it should not be your only criterion for food choice. You should also consider the total amount of carbohydrate too when selecting what to eat. While glycemic index can help make food choices, the glycemic load can help you to work out the portion size.

You can benefit by eating foods that have lower GL and GI. But remember, there is no one diet plan that suits all. Portion sizes vary from person to person. Variety, processing, cooking method, other foods consumed simultaneously, time of consumption, etc. can all affect a food item’s GI and influence how it affects your blood sugar response. So, calculate your own GL and follow a tailor-made diet plan based on your preferences. Include fruits, vegetables, whole grains, etc. Pay attention to the fibre and salt content, and quantity and type of fat as well.

Can diabetics eat foods with a high GI but low GL?

For a long time certain foods loaded with important nutrients and fibre — such as some fruits — got a bad rap because of their high GI, which is not based on their actual serving size. Thanks to the GL, they are not ‘bad’ anymore and are safe to eat for people with diabetes. One serving of these food items don’t contain much carbohydrate and hence won’t have much effect on your blood sugar.

Some of the examples are: ^[1]

Read the full list of healthy fruits that are good for your blood sugar levels here.

The International table of glycemic index and glycemic load values: 2002 lists the GI and GL of various foods.^[1] There is a revised International table of glycemic index and glycemic load values: 2008 ^{[3, 4]}

References:

1. http://www.diabetes.org.br/publico/images/pdf/2016/nutr-2002-foster-powell-5-56.pdf
2. Willett W, Manson J, Liu S. Glycemic index, glycemic load, and risk of type 2 diabetes. Am J Clin Nutr. 2002 Jul;76(1):274S-80S. Review. PubMed PMID: 12081851.
3. Atkinson FS, Foster-Powell K, Brand-Miller JC. International Tables of Glycemic Index and Glycemic Load Values: 2008. Diabetes Care. 2008;31(12):2281-2283. doi:10.2337/dc08-1239.
4. http://www.beauty-review.nl/wp-content/uploads/2014/07/Revised-International-Table-of-Glycemic-Index-GI-and-Glycemic-Load-GL-Values%E2%80%942002.pdf