What Is GI and GL? (Simplified Explanation)

what is gi and gl

Are glycemic Index (GI) and glycemic load (GL) two terms that confuse you?  Do you need a simple explanation on what they are and how they are calculated? My name is LeeAnna. I am a Registered Dietitian, as well as a Diabetes Care and Education Specialist. I wrote this quick article just for you to simplify the answer. What is GI and GL?

As a whole, glycemic index refers to a blood sugar index, which measures the effects of carbohydrate foods on a person’s blood sugar. The glycemic load goes a step further by including the amount of carbohydrate in the food with the glycemic index.

What is Glycemic Index?

GI became popular in the 1980’s after research was conducted to determine which foods were most beneficial for people with diabetes. The studies included measuring and observing the blood glucose results of various test subjects after eating the same amount of carbohydrate, but from different food sources. Each participant would consume 50 g of a standard food portion and their blood glucose was measured for the following three hours, in regular increments.

The glycemic index (GI) is a number ranging from 0 to 100, assigned to a food. Pure glucose (sugar) was given the value of 100. This represents the relative rise in the blood glucose level two hours after consuming a food.

Water, which does not affect blood glucose levels, has a GI value of 0, while foods such as parsnips or baguettes have values in the high 90’s. Peanuts have a GI value of 13 or 14 depending on preparation, which means they have a low impact on blood glucose levels

The Glycemic index itself is not a diet, but one of various tools, such as calorie counting or carbohydrate counting for guiding food choices. where a low GI food ranges from a number of 1 to 55. A medium GI food ranges from 56 to 69, and a high GI food is valued at 70 or higher.

The purpose of the glycemic index is to allow people to see how likely a food is to cause large increases in blood sugar levels. Unfortunately, the GI does not necessarily specify portion sizes or an optimal number of calories, proteins, or fats.

Water, opposite pure sugar, has a GI value of 0, which does not affect blood sugar. Foods that fall into the three categories of GI include the following:

GI values are divided into 3 categories:

  • LOW GI FOODS: (1-55) include green vegetables, raw carrots, most fruits, chickpeas, kidney beans or lentils, and whole-grain or bran cereal.
  • MEDIUM GI FOODS: (56-69) include bananas, sweet corn, pineapple, raisins, oat cereal, multigrain or Rye bread.
  • HIGH GI FOODS: (70-100) generally include white bread, white rice, and potatoes.

About 90-100% of carbohydrates break down to blood glucose. GI is a reference for carbohydrate-containing foods. Fats, such as butter and oils, and proteins, such as meat and fish, do not affect the blood sugar and are not significant when measuring GI. Most of these foods are assigned the value of 0. You will notice that the same product, made with different ingredients, will give you a different GI. For example, an English muffin made with white flour has a GI value of 77. A whole wheat English muffin has a GI value of 45.

GI will vary in the same food depending on any number of factors, including whether the food is cooked or raw, how long the food is cooked, fiber content, food processing, shape, and density. In general, foods that are cooked longer will have a higher GI. Foods that are more dense will tend to have a higher GI.

Due to the many variations of different foods, using GI as a weight loss plan not reliable. The Academy of Nutrition and Dietetics does not endorse the GI Method by itself, but can be utilized if a calorie restriction is in place.

Adding fat and protein to a food will lower the GI. Mashed potatoes, for example, have a high GI. Mashed potatoes with gravy and meatballs will have a much lower GI.

Ripeness of a fruit or vegetable will effect the GI. Generally speaking, “the riper the fruit, the higher the GI.” Similarly, the pH of the food plays a role. Usually, the lower the pH (more acidic), the lower the GI. For example, adding vinegar to a food will lower the glycemic index of that food.

My Dietitian TIP: When counseling patients who question glycemic index, I explain what it is, but I also tell them not to be overly concerned about GI values for all foods. I use carrots as an example. Yes, carrots have a high glycemic index number, but unless you are eating an entire bag of carrots by itself, it will not likely have an impact on your blood glucose. Like adding gravy and meatballs to your mashed potatoes, including carrots with different proteins and fats will essentially “balances out” the high GI of the carrots.

What Is Glycemic Load?

The glycemic load (GL) is a formula that corrects for a potentially misleading GI by combining the portion size with the GI into one number.

The (GL) of a food is calculated by the GI multiplied by the number of carbohydrates the food contains and then divided by 100. The lower the GL, the better, and it means the less impact it will have on your blood sugar levels over a sustained period of time.

GL values are divided into 3 categories:

  • LOW GL foods: (10 or less)
  • MEDIUM GL foods: (11-19)
  • HIGH GL foods: (20 or greater)

Glycemic Load Calculation Examples

* One fresh large peach example:

(4 oz) with 15 g of carbohydrate and a GI of 42:

How To Calculate Glycemic Load On A Peach

GL Calculation = 15×42 = 630  630÷100 = 6.3

* One small potato example:

(3 oz) with 15 g of carbohydrate and a GI of 92:

How To Calculate Glycemic Load On a Small Potato

GL Calculation = 15×92 = 1380 1380÷100 = 13.8

Final Thoughts

Calculating glycemic load can be troublesome, and using glycemic index can be confusing. Using GI and GL may be helpful if they are used with evidence-based approaches to manage weight, cardiac health, and diabetes. However, I recommend consuming more unprocessed foods and high-fiber foods, practice portion control, and increase self-monitoring to see your progress or keep yourself accountable.

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