Diabetes Nutrition Guide: Understanding the Glycemic Index

Diabetes Nutrition Guide: What Is the Glycemic Index (GI)?

The glycemic index (GI) is one nutritional tool you can use to help rate the quality of carbohydrates that you eat. The index measures how quickly the carbohydrates in a specific food impact your blood sugar. They are rated low, medium, or high, depending on how quickly they raise your blood sugar level, compared to either glucose or white bread (these foods have a glycemic index rating of 100). By choosing low glycemic index foods, you can minimize dramatic increases in your blood sugar. Additionally, if you eat a high glycemic index food, you can expect that it will increase your blood sugar more significantly. It may also cause a higher post-meal blood sugar reading.

Many factors can change the glycemic index of a food. These factors include its composition and how the food is cooked. The glycemic index of food also changes when it is mixed together.

The glycemic index of food is not based on a normal serving of a particular food. For example, carrots have a high glycemic index, but to get the amount measured for carrot’s glycemic index you would have to eat a pound and a half. A different measure, called glycemic load, is also available. This measure takes into account both the speed of digestion and the amount present in a normal serving of a food. It may be a better way to measure the impact a carbohydrate food has on blood sugar.



What Factors Affect a Food’s Glycemic Index Rating?

To assign a GI number, foods are assigned to one of three categories: low, medium, or high.

  • low GI foods: have a GI of 55 or less
  • medium GI foods: between 56 and 69
  • high GI foods: 70 or higher

For glycemic load, under 10 is considered low, 10 to 20 is considered medium, and over 20 is consider high.

Several factors are taken into account when assigning a food a glycemic rating.

These factors include:


Foods that are highly acidic, such as pickles, tend to be lower on the GI than foods that are not. This explains why breads made with lactic acid, such as sourdough bread, are lower on the GI than white bread.

Cooking Time

The longer a food is cooked, the higher it tends to be on the GI. When a food is cooked, the starch or carbohydrates start to break down.

Fiber Content

In general, foods that are high in fiber have lower glycemic ratings. The fibrous coatings around beans and seeds mean the body breaks them down more slowly. Therefore, they tend to be lower on the glycemic scale than foods without this coating.


As a general rule, the more processed a food is, the higher it is on the glycemic scale. For example, fruit juice has a higher GI rating than fresh fruits.


The more ripe a fruit or vegetable, the higher it tends to be on the GI.

While there are certainly exceptions to each rule, these are some general guidelines to follow when evaluating the potential blood sugar impact of a particular food.

How it Works

How Does Using the Glycemic Index Work?

Eating according to the GI can help you better manage your post-meal blood sugar levels. The GI can also help you determine appropriate combinations of food. For example, eating several low GI fruits and vegetables combined with a high GI food can help you maintain better blood sugar control. Other examples include adding beans to rice, a nut butter to bread, or tomato sauce to pasta.



What Are the Benefits of Using the Glycemic Index?

Choosing foods with low glycemic impact can help to keep your blood sugar levels low. However, you must also carefully adhere to the portion sizes recommended. Glycemic ratings are not only for those with diabetes. Those trying to lose weight or decrease hunger also utilize the GI as a diet because it can control appetite. Because the food takes longer to digest in the body, a person can feel fuller, longer.


What Are the Risks of Eating on the Glycemic Index?

The glycemic index helps you pick higher quality carbohydrates. However, it is the total carbohydrate loads in your diet that ultimately affect blood sugar levels. Choosing low glycemic foods can help, but you must also manage the total carbohydrates that you consume. Also, the GI does not take into account the overall nutritional value of a food. For example, just because microwave popcorn is in the middle of GI foods, doesn’t mean you should live only on microwave popcorn.

When you start on a diet to manage your diabetes, the American Diabetes Association recommends that you meet with a registered dietician who is familiar with diabetes. There are many meal plans available. Make sure to ask how you can use information on the glycemic index to best manage your blood sugar levels.


Fruits and Vegetables

The Glycemic Index of Common Fruits and Vegetables

Eating healthy is important to controlling diabetes. Fruits and vegetables are an important part of a healthy diet. Knowing both the glycemic index as well as the glycemic load of some of the more common fruits and vegetables will help you choose your favorites to incorporate into your daily diet. According to the Harvard Health Publication, they are as follows:

FRUITS Glycemic index (glucose = 100) Serving size (grams) Glycemic load per serving
Apple, average 39 120 6
Banana, ripe 62 120 16
Dates, dried 42 60 18
Grapefruit 25 120 3
Grapes, average 59 120 11
Orange, average 40 120 4
Peach, average 42 120 5
Peach, canned in light syrup 40 120 5
Pear, average 38 120 4
Pear, canned in pear juice 43 120 5
Prunes, pitted 29 60 10
Raisins 64 60 28
Watermelon 72 120 4
VEGETABLES Glycemic index (glucose = 100) Serving size (grams) Glycemic load per serving
Green peas, average 51 80 4
Carrots, average 35 80 2
Parsnips 52 80 4
Baked russet potato, average 111 150 33
Boiled white potato, average 82 150 21
Instant mashed potato, average 87 150 17
Sweet potato, average 70 150 22
Yam, average 54 150 20



When you use the glycemic index when planning meals, you will be able to better manage your blood sugar levels. You will also be able to find and choose foods that you enjoy. You can then incorporate them into a healthy diet plan. Managing blood sugar levels through diet is an extremely important part of managing your diabetes.

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