Diabetes Nutrition Guide: Understanding the Glycemic Index
The glycemic index is one tool you can use to help rate the quality of carbohydrates that you eat.

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What Is The Glycemic Index?

The glycemic index is one tool you can use to help rate the quality of carbohydrates that you eat. The index measures the 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. By choosing low-glycemic index foods, you can minimize dramatic increases in your blood sugar. Conversely, if you eat a high-glycemic index food, you can expect that it will increase your blood sugar more significantly and may cause a higher post-meal blood sugar reading.

Many factors can change the glycemic index of a food, including 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 of carbohydrate 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, and 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 glycemic index (GI), foods are assigned to one of three categories: low, medium or high. Low glycemic index foods are those that have a GI of 55 or less. Medium GI foods are between 56 and 69. High GI foods are 70 or higher. For glycemic load,  under 10 is considered low, 10 to 20 in considered medium, and over 20 is consider high.

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

  • Acidity. 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.
  • Process: 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.
  • Ripeness: 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 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.

Listed below are some common food with both their glycemic index and glycemic load. Figures are based on 100 grams of carbohydrate.

Food

Glycemic Index Ranking

Glycemic Load Rating

Apple

39

6 (4 ounce apple)

Bagel, white

69

25 (2 ½  ounces)

Baked russet potato

111

33 (5 ounces)

Banana

62

16 (4 ounce or 1/2 small )

Black beans

30

7 (5 ounces )

Carrots

35

2 (1/3 cup)

Coca-Cola

63

16 (8 ounces)

Gatorade

78

12 (8 ounces )

Grapes

59

11 (4 ounces)

Hamburger bun

61

9 (1 ounce)

Hummus

6

0 (2 tablespoons)

Instant mashed potatoes

87

17 (1/2 cup)

Instant oatmeal

83

30 (1 cup)

Microwave popcorn, plain

55

6 (20 grams/One-third an average bag)

Navy beans

31

9 (5 ounces )

Orange

40

4 (4 ounce orange)

Orange juice

46

12 (1 cup)

Peach

42

5 (4 ounce peach)

Pita bread, white

68

10 ( 1 ounce)

Raisins

64

28 (2 ounces)

Soybeans

15

1 (5 ounces)

Sweet potato

70

22 (5 ounces)

What Are the Benefits of Using the Glycemic Index?

Choosing foods with low glycemic impact can help to keep your blood sugar levels low, providing you carefully follow 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?

While the glycemic index can help you pick higher quality carbohydrates, it is the total carbohydrate loads in your diet that ultimately affects blood sugar levels. While choosing low glycemic foods can help, 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 solely off microwave popcorn.

If you are starting 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.

Written by: Rachel Nall, RN, BSN
Edited by:
Medically Reviewed by: Peggy Pletcher, MS, RD, LD, CDE
Published: May 8, 2014
Published By: Healthline Networks, Inc.
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