What is the Glycemic Index?

Introduction

Glycemic Index (GI) is a measurement carried out on carbohydrate-containing foods and their impact on our blood sugar. GI is a relatively new way of analyzing foods. Previously, most meal plans designed to improve blood sugar analyzed the total amount of carbohydrates (including sugars and starches) in the foods themselves. GI goes beyond this approach, looking at the impact of foods on our actual blood sugar. In other words, instead of counting the total amount of carbohydrates in foods in their unconsumed state, GI measures the actual impact of these foods on our blood sugar. Each food in the WHF database is classified as very low, low, medium, or high GI. Individual GI values appear in the DRI%/DV% bar chart at the top of each food profile page.

Over the past 15 years, low-GI diets have been associated with decreased risk of cardiovascular disease, type 2 diabetes, metabolic syndrome, stroke, depression, chronic kidney disease, formation of gall stones, neural tube defects, formation of uterine fibroids, and cancers of the breast, colon, prostate, and pancreas. Choosing whole, unprocessed foods that are low or very low GI is a practical way to take advantage of these associations. All WHF, including herbs and spices, are classified into one of four GI categories for easy reference.

Typically, a food is consumed in whatever serving size will provide 50 grams (about 1.8 ounces) of available carbohydrates. Available carbohydrates (or avCHOs) are carbohydrates that get readily digested, absorbed, and metabolized by our body. These carbohydrates have a much greater impact on our blood sugar level than carbohydrates in general because carbohydrates in general include substances that aren’t readily digested, absorbed, and metabolized. Insoluble fibers, for example, are carbohydrates that do not have an immediate impact on our blood sugar level because they cannot be readily digested. As a very general way of estimating available carbohydrates in a serving of food, researchers take the total amount of carbohydrates and subtract out the total amount of fiber. Available carbohydrates are what’s left.

After 50 grams of available carbohydrates have been consumed, blood sugar levels are measured over a period of 2 hours. The results are plotted on a graph and summarized in what is called glucose AUC, or “area under the curve.” Glucose AUC shows the immediate impact of the food on our blood sugar.

Measuring GI also requires a second step. In this second step, 50 grams of available carbohydrate are consumed, but this time the food involved is one of two reference foods: either white bread or pure sugar (pure glucose). Once again, blood sugar levels are measured over a period of 2 hours, and the glucose AUC is calculated. At this point, it is possible to compare the two results. The impact of the first food on our blood sugar is compared to the impact of either white bread or glucose itself. When these two results are compared, the impact of the white bread or glucose is arbitrarily given a value of 100 to make the comparison easier. As an example, let’s say that researchers are trying to establish a GI for green peas and they decide to compare the impact of green peas on blood sugar to the impact of white bread. And in this example, let’s say that a person consumes a starchy vegetable like green peas, and the glucose AUC (area under the curve) is 48% as large the glucose AUC when white bread is consumed. In this case, the GI for green peas would be established at 48% of 100, or 48. (In fact, this is precisely the GI that we use for green peas at WHF.)

GI rating system

Most healthcare organizations use a “high,” medium” and “low” rating system for GI. Using this system, foods get classified in the following way:

Low GI

Medium GI

High GI

0-55

56-69

70 or greater

The WHF rating system uses this same three-tier framework as its foundation, with the addition of a “very low” category. Since over one-third of WHF are vegetables with very small amounts of available carbohydrate (avCHO), the “very low GI” classification captures foods with less than 5 g avCHO per 100 g serving. AvCHO is calculated as total carbohydrate minus total fiber. The “low” category applies to foods with 5-12 g avCHO, or foods with a published GI of 55 or below, or foods for which the preponderance of research demonstrates a beneficial impact on blood sugar regardless of avCHO level. The summary chart below shows the full classification criteria.

Glycemic index rating system

Very Low GI

Low GI

Medium GI

High GI

Criteria for Classification

No established GI value and an available carbohydrate (avCHO) of less than 5 grams OR an established GI of less than 20 and an avCHO of less than 7 grams

Either an established GI value of 55 or less OR an available carbohydrate (avCHO) value greater or more than 5 grams but less than or equal to 12 grams OR a beneficial impact on blood sugar in a preponderance of research studies

An established GI vale of 56-69

An established GI value of 70 or greater

One of the most interesting aspects of GI involves its relationship to the unique features of carbohydrates. Carbohydrates are definitely not the same with respect to their immediate impact on our blood sugar. For example, non-whole grain breads and pasta noodles both contain similar amounts of starch, and their starches are similarly composed of long chains of the simple sugar, glucose. But the 3-dimensional structure of bread allows more of the starch to be exposed to enzymes in our saliva and in our digestive tract. This greater exposure to enzymes allows more of the starch to be broken down into sugar and gives non-whole grain breads a generally higher GI value than non-whole grain pastas. Similarly, two basic types of starch found in many foods - amylose and amylopectin - also influence their GI values, even if the foods have identical amounts of total starch.

With respect to their GI, foods are also differently impacted by cooking. Many legumes, for example, have cell structures that are fairly resistant to disruption and help prevent breakdown of the starches inside their cells. For this reason, legumes tend to have lower-than-expected GI values, provided that they have not been overcooked. Before they have been ground into flour, whole grains also tend to have lower GI values due to the sturdiness of their cell structures. But after being ground into flour, their starches become more susceptible to breakdown and their GI value tends to increase. Of course, these descriptions are generalizations and can be different for specific legumes, specific grains, and specific flours. Still, they reflect a general pattern and principle: namely, that for a carbohydrate-containing food, the more its natural integrity becomes disrupted by processing or overcooking, the more its GI value is likely to be increased. Minimal disruption of whole foods from their natural, unprocessed state is one of our key principles at WHF, and it is a principle 100% aligned with promotion of lower GI values.

GI ratings for the WHF

Food Group

Very Low GI

Low GI

Medium GI

High GI

WHF

Vegetables

asparagus

carrots

beets

potatoes

avocados

eggplant

corn

beet greens

garlic

leeks

bell peppers

green peas

sweet potatoes

bok choy

onions

broccoli

sea vegetables

Brussels sprouts

winter squash

cabbage

cauliflower

celery

collard greens

cucumbers

fennel (bulb)

green beans

kale

mushrooms, crimini

mustard greens

olives

olive oil

Romaine and other lettuce

spinach

summer squash

Swiss chard

tomatoes

turnip greens

Fruits

apples

apricots

bananas

cantaloupe

blueberries

figs

cranberries

papaya

grapefruit

pineapple

grapes

watermelon

kiwifruit

lemons/limes

oranges

pears

plums & prunes

raspberries

strawberries

Nuts & Seeds

flaxseeds

almonds

sesame seeds

cashews

peanuts

pumpkin seeds

sunflower seeds

walnuts

Beans & Legumes

soybeans

black beans

tofu

dried peas

tempeh

garbanzo beans

kidney beans

lentils

lima beans

navy beans

pinto beans

Seafood

cod

scallops

salmon

sardines

shrimp

tuna

Meats

beef, grass-fed

chicken-pasture-raised

lamb, grass-fed

turkey, pasture-raised

Dairy

cheese, grass-fed

eggs, pasture-raised

cow’s milk, grass-fed

yogurt, grass-fed

Grains

barley

millet

brown rice

buckwheat

oats

quinoa

rye

whole wheat

World’s Healthiest Spices and Herbs

black pepper

chili pepper

cilantro & coriander seeds

cinnamon

cloves

cumin seeds

dill

ginger

mustard seeds

oregano

parsley

peppermint

rosemary

sage

thyme

turmeric

Much of the pioneering work on glycemic index was carried out by Professor Jennie Brand-Miller,PhD, Personal Chair in Human Nutrition in the Human Nutrition Unit, School of Molecular and Microbial Biosciences at the University of Sydney in Sydney, Australia. The glycemic index website at the University of Sydney provides extensive information about her work as well as a searchable database for GI values.

David Mendosa’s website on glycemic index, glycemic load, and diabetes management also provides food GI databases.

Atkinson FS, Foster-Powell K, Brand-Miller JC. International Tables of Glycemic Index and Glycemic Load Values: 2008. Diabetes Care 2008; 31(12).

Foster-Powell K, Holt HA, and Brand-Miller JC. International table of glycemic index and glycemic load values: 2002. Am J Clin Nutr2002;76:5—56.

Human Nutrition Unit, School of Molecular Biosciences, University of Sydney, Sydney, Australia. (2013). GI Foods Advanced Search Database. Online at http://www.glycemicindex.com/foodSearch.php.

National Cancer Institute (NCI). DHQ Nutrient Database. Applied Research: Cancer Control and Populations Sciences. National Institutes of Health, Bethesda, MD. Available online at: http://appliedresearch.cancer.gov/DHQ/database/

In Addition We Used the Following Non-Database References

Castro-Quezada I, Sanchez-Villegas A, Diaz-Gonzalez V, et al. Relationship between dietary glycemic index, dietary glycemic load and major cardiovascular events in the PREDIMED study. European Geriatric Medicine, Volume 4, Supplement 1, September 2013, Pages S128-S129.

Frost G and Dornhorst A. Glycemic Index. Encyclopedia of Human Nutrition (Third Edition), 2013, Pages 393-398.

Kumar SB and Prabhansankar P. Low glycemic index ingredients and modified starches in wheat based food processing: A review Review. Trends in Food Science & Technology, Volume 35, Issue 1, January 2014, Pages 32-41.

Lin CS, Kimokoti RW, Brown LS, et al. Methodology for Adding Glycemic Index to the National Health and Nutrition Examination Survey Nutrient Database. Journal of the Academy of Nutrition and Dietetics, Volume 112, Issue 11, November 2012, Pages 1843-1851.

Ma XY, Liu JP, and Song ZY. Glycemic load, glycemic index and risk of cardiovascular diseases: Meta-analyses of prospective studies. Atherosclerosis, Volume 223, Issue 2, August 2012, Pages 491-496.

O’Reilly J, Wong SH, and Chen Y. Glycaemic index, glycaemic load and exercise performance. Sports Med. 2010 Jan 1;40(1):27-39.

Wolever TM. Is glycaemic index (GI) a valid measure of carbohydrate quality? Eur J Clin Nutr. 2013 May;67(5):522-31. doi: 10.1038/ejcn.2013.27. Epub 2013 Feb 13.

Topics

Discussion

What is the glycemic index (gi)?

Glycemic Index (GI) is a measurement carried out on carbohydrate-containing foods and their impact on our blood sugar. GI is a relatively new way of analyzing foods. Previously, most meal plans designed to improve blood sugar analyzed the total amount of carbohydrates (including sugars and starches) in the foods themselves. GI goes beyond this approach, looking at the impact of foods on our actual blood sugar. In other words, instead of counting the total amount of carbohydrates in foods in their unconsumed state, GI measures the actual impact of these foods on our blood sugar. Each food in the WHF database is classified as very low, low, medium, or high GI. Individual GI values appear in the DRI%/DV% bar chart at the top of each food profile page.

Why is GI important?

Over the past 15 years, low-GI diets have been associated with decreased risk of cardiovascular disease, type 2 diabetes, metabolic syndrome, stroke, depression, chronic kidney disease, formation of gall stones, neural tube defects, formation of uterine fibroids, and cancers of the breast, colon, prostate, and pancreas. Choosing whole, unprocessed foods that are low or very low GI is a practical way to take advantage of these associations. All WHF, including herbs and spices, are classified into one of four GI categories for easy reference.

How is GI measured?

Typically, a food is consumed in whatever serving size will provide 50 grams (about 1.8 ounces) of available carbohydrates. Available carbohydrates (or avCHOs) are carbohydrates that get readily digested, absorbed, and metabolized by our body. These carbohydrates have a much greater impact on our blood sugar level than carbohydrates in general because carbohydrates in general include substances that aren’t readily digested, absorbed, and metabolized. Insoluble fibers, for example, are carbohydrates that do not have an immediate impact on our blood sugar level because they cannot be readily digested. As a very general way of estimating available carbohydrates in a serving of food, researchers take the total amount of carbohydrates and subtract out the total amount of fiber. Available carbohydrates are what’s left.

After 50 grams of available carbohydrates have been consumed, blood sugar levels are measured over a period of 2 hours. The results are plotted on a graph and summarized in what is called glucose AUC, or “area under the curve.” Glucose AUC shows the immediate impact of the food on our blood sugar.

Measuring GI also requires a second step. In this second step, 50 grams of available carbohydrate are consumed, but this time the food involved is one of two reference foods: either white bread or pure sugar (glucose). Once again, blood sugar levels are measured over a period of 2 hours, and the glucose AUC is calculated. At this point, it is possible to compare the two results. The impact of the first food on our blood sugar is compared to the impact of either white bread or glucose itself. When these two results are compared, the impact of the white bread or glucose is arbitrarily given a value of 100 to make the comparison easier. As an example, let’s say that researchers are trying to establish a GI for green peas and they decide to compare the impact of green peas on blood sugar to the impact of white bread. And in this example, let’s say that a person consumes a starchy vegetable like green peas, and the glucose AUC (area under the curve) is 48% as large the glucose AUC when white bread is consumed. In this case, the GI for green peas would be established at 48% of 100, or 48. (In fact, this is precisely the GI that we use for green peas at WHF.)

GI rating system

Most healthcare organizations use a “high,” medium” and “low” rating system for GI. Using this system, foods get classified in the following way:

Low GI

Medium GI

High GI

0-55

56-69

70 or greater

The WHF rating system uses this same three-tier framework as its foundation, with the addition of a “very low” category. Since over one-third of WHF are vegetables with very small amounts of available carbohydrate (avCHO), the “very low GI” classification captures foods with less than 5 g avCHO per 100 g serving. AvCHO is calculated as total carbohydrate minus total fiber. The “low” category applies to foods with 5-12 g avCHO, or foods with a published GI of 55 or below, or foods for which the preponderance of research demonstrates a beneficial impact on blood sugar regardless of avCHO level. The summary chart below shows the full classification criteria.

Glycemic index rating system

Very Low GI

Low GI

Medium GI

High GI

Criteria for Classification

No established GI value and an available carbohydrate (avCHO) of less than 5 grams OR an established GI of less than 20 and an avCHO of less than 7 grams

Either an established GI value of 55 or less OR an available carbohydrate (avCHO) value greater or more than 5 grams but less than or equal to 12 grams OR a beneficial impact on blood sugar in a preponderance of research studies

An established GI vale of 56-69

An established GI value of 70 or greater

Why do some GI values seem surprising?

One of the most interesting aspects of GI involves its relationship to the unique features of carbohydrates. Carbohydrates are definitely not the same with respect to their immediate impact on our blood sugar. For example, non-whole grain breads and pasta noodles both contain similar amounts of starch, and their starches are similarly composed of long chains of the simple sugar, glucose. But the 3-dimensional structure of bread allows more of the starch to be exposed to enzymes in our saliva and in our digestive tract. This greater exposure to enzymes allows more of the starch to be broken down into sugar and gives non-whole grain breads a generally higher GI value than non-whole grain pastas. Similarly, two basic types of starch found in many foods - amylose and amylopectin - also influence their GI values, even if the foods have identical amounts of total starch.

With respect to their GI, foods are also differently impacted by cooking. Many legumes, for example, have cell structures that are fairly resistant to disruption and help prevent breakdown of the starches inside their cells. For this reason, legumes tend to have lower-than-expected GI values, provided that they have not been overcooked. Before they have been ground into flour, whole grains also tend to have lower GI values due to the sturdiness of their cell structures. But after being ground into flour, their starches become more susceptible to breakdown and their GI value tends to increase. Of course, these descriptions are generalizations and can be different for specific legumes, specific grains, and specific flours. Still, they reflect a general pattern and principle: namely, that for a carbohydrate-containing food, the more its natural integrity becomes disrupted by processing or overcooking, the more its GI value is likely to be increased. Minimal disruption of whole foods from their natural, unprocessed state is one of our key principles at WHF, and it is a principle 100% aligned with promotion of lower GI values.

GI ratings for the WHF

Food Group

Very Low GI

Low GI

Medium GI

High GI

WHF

Vegetables

asparagus

carrots

beets

potatoes

avocados

eggplant

corn

beet greens

garlic

leeks

bell peppers

green peas

sweet potatoes

bok choy

onions

broccoli

sea vegetables

Brussels sprouts

winter squash

cabbage

cauliflower

celery

collard greens

cucumbers

fennel (bulb)

green beans

kale

mushrooms, crimini

mustard greens

olives

olive oil

Romaine and other lettuce

spinach

summer squash

Swiss chard

tomatoes

turnip greens

Fruits

apples

apricots

bananas

cantaloupe

blueberries

figs

cranberries

kiwifruit

grapefruit

papaya

grapes

pineapple

lemons/limes

raisins

oranges

watermelon

pears

plums

prunes

raspberries

strawberries

Nuts & Seeds

flaxseeds

almonds

sesame seeds

cashews

peanuts

pumpkin seeds

sunflower seeds

walnuts

Beans & Legumes

soybeans

black beans

tofu

dried peas

tempeh

garbanzo beans

kidney beans

lentils

lima beans

navy beans

pinto beans

Seafood

cod

scallops

salmon

sardines

shrimp

tuna

Meats

beef, grass-fed

chicken-pasture-raised

lamb, grass-fed

turkey, pasture-raised

Dairy

cheese, grass-fed

eggs, pasture-raised

cow’s milk, grass-fed

yogurt, grass-fed

Grains

barley

millet

brown rice

buckwheat

oats

quinoa

rye

whole wheat

World’s Healthiest Spices and Herbs

black pepper

cayenne & chili pepper

cilantro & coriander seeds

cinnamon

cloves

cumin seeds

dill

ginger

mustard seeds

oregano

parsley

peppermint

rosemary

sage

thyme

turmeric

Where can I find out more about gi?

Much of the pioneering work on glycemic index was carried out by Professor Jennie Brand-Miller,PhD, Personal Chair in Human Nutrition in the Human Nutrition Unit, School of Molecular and Microbial Biosciences at the University of Sydney in Sydney, Australia. The glycemic index website at the University of Sydney provides extensive information about her work as well as a searchable database for GI values.

David Mendosa’s website on glycemic index, glycemic load, and diabetes management also provides food GI databases.

References

For Established Glycemic Index values, We Used the Following Databases and Publications

Atkinson FS, Foster-Powell K, Brand-Miller JC. International Tables of Glycemic Index and Glycemic Load Values: 2008. Diabetes Care 2008; 31(12).

Foster-Powell K, Holt HA, and Brand-Miller JC. International table of glycemic index and glycemic load values: 2002. Am J Clin Nutr2002;76:5—56.

Human Nutrition Unit, School of Molecular Biosciences, University of Sydney, Sydney, Australia. (2013). GI Foods Advanced Search Database. Online at http://www.glycemicindex.com/foodSearch.php.

National Cancer Institute (NCI). DHQ Nutrient Database. Applied Research: Cancer Control and Populations Sciences. National Institutes of Health, Bethesda, MD. Available online at: http://appliedresearch.cancer.gov/DHQ/database/

In Addition We Used the Following Non-Database References

Castro-Quezada I, Sanchez-Villegas A, Diaz-Gonzalez V, et al. Relationship between dietary glycemic index, dietary glycemic load and major cardiovascular events in the PREDIMED study. European Geriatric Medicine, Volume 4, Supplement 1, September 2013, Pages S128-S129.

Frost G and Dornhorst A. Glycemic Index. Encyclopedia of Human Nutrition (Third Edition), 2013, Pages 393-398.

Kumar SB and Prabhansankar P. Low glycemic index ingredients and modified starches in wheat based food processing: A review Review. Trends in Food Science & Technology, Volume 35, Issue 1, January 2014, Pages 32-41.

Lin CS, Kimokoti RW, Brown LS, et al. Methodology for Adding Glycemic Index to the National Health and Nutrition Examination Survey Nutrient Database. Journal of the Academy of Nutrition and Dietetics, Volume 112, Issue 11, November 2012, Pages 1843-1851.

Ma XY, Liu JP, and Song ZY. Glycemic load, glycemic index and risk of cardiovascular diseases: Meta-analyses of prospective studies. Atherosclerosis, Volume 223, Issue 2, August 2012, Pages 491-496.

O’Reilly J, Wong SH, and Chen Y. Glycaemic index, glycaemic load and exercise performance. Sports Med. 2010 Jan 1;40(1):27-39.

Wolever TM. Is glycaemic index (GI) a valid measure of carbohydrate quality? Eur J Clin Nutr. 2013 May;67(5):522-31. doi: 10.1038/ejcn.2013.27. Epub 2013 Feb 13.