Glycemic Index

Overview

If you have diabetes or prediabetes, you likely know all too well the importance of watching your blood sugar levels and being intentional about what you eat. That’s where the glycemic index can come in handy, as it assigns foods a number between 0 and 100, indicating its potential effect on blood sugar levels.

However, while helpful, the glycemic index provides a limited look at just one factor affecting blood sugar.

Learn more about the glycemic index below, which foods tend to cause a spike in blood sugar (or not) and the limitations of this measurement.

What Is the Glycemic Index?

The glycemic index measures how quickly foods that contain carbohydrates can increase your blood sugar. The scale is 0 to 100.

Foods can fall into one of three categories:

Low: 55 and below

Moderate: 56 to 75

High: 76 and above

Foods with a low GI typically release sugar slowly when consumed, causing a slower increase in blood sugar. Foods with a high GI release glucose more rapidly and cause a quick increase in blood sugar levels.

A slow and steady increase in blood sugar, compared to rapid increases and drops, also reduces sugar cravings, supports hormonal balance and helps prevent conditions like cardiovascular disease and type 2 diabetes.

Essentially, the glycemic index shows that not everything that contains the exact same amount of grams of carbs will behave the same way in your body. You can measure how your body responds to a cup of orange juice versus how it reacts to other food items: a banana, 25 grams of candy or 25 grams of whole-grain bread.

The reason for these differences comes from how carbs react in your body. Simple carbohydrates — say, the sugars found in soda and sweet desserts — are broken down faster than the more complex carbohydrates found in some vegetables and whole-grain foods. As a result, your blood sugar spikes and then falls rapidly. Over time, doctors believe these constant surges and retreats play a part in people becoming insulin resistant.

Glycemic Index vs. Glycemic Load

To counteract some of the issues with glycemic index, researchers developed the glycemic load (GL) measurement. Unlike GI, GL accounts for the quantity of the food being eaten.5 The main difference between GI and GL is:

Glycemic index is based on eating 50 grams of a specific food

Glycemic load is based on eating a standard serving size of a specific food

Glycemic load is calculated by multiplying the GI value by the number of carbohydrates (in grams) per serving, then dividing that number by 100.

What is Glycemic Load?

The glycemic load (GL) is a more accurate tool for assessing the impact of eating carbohydrates. It gives a more complete picture than does glycemic index alone, because it accounts for the amount of carbohydrate in a serving. A GI value indicates only how rapidly a particular carbohydrate turns into sugar, whereas GL accounts for how much of that carbohydrate a person would typically eat. The carbohydrate in watermelon, for example, has a high GI. However, there is not a lot of sugar in a serving of watermelon, since most of it is fiber and water. Thus watermelon’s glycemic load is relatively low.

Foods that have a low GL almost always have a low GI. In contrast, foods with an intermediate or high GL can have a GI that ranges from very low to very high.

Glycemic Load	Range
Low	0 - 10
Medium	11 - 19
High	20 & over

Glycemic Load Chart for Common Foods

The following charts highlight low, medium, and high GL foods based on data from the Linus Pauling Institute at Oregon State University.7

Low-GL Foods (10 or less)
Foods	GL
Apple	6
Carrots, boiled	1
Cashews	2
Kidney beans	8
Lentils, dried and boiled	7
Orange	5
Peanuts	1
Pear	4
Skim milk	4
Watermelon	8
White bread (wheat)	10

Medium-GL Foods (11 to 19)
Foods	GL
Banana	13
Pearled barley, boiled	11
Puffed rice cake	17
Spaghetti, whole wheat	14

High-GL Foods (20 or more)
Foods	GL
Brown rice	20
Cornflakes	20
Dates	25
Potato, boiled	25
Spaghetti	20
White Rice	35

Why Are These Numbers Important?

A low glycemic index diet has been associated with improvements in:

Obesity

Type 2 Diabetes

Gestational Diabetes

Metabolic Syndrome

PCOS

NAFLD

Dyslipidemia

Hypoglycemia

Conversely, diets with high glycemic index or glycemic load are strongly associated with type 2 diabetes incidence. Dietary glycemic index is also positively associated with the prevalence of metabolic syndrome, though according to one review, a significant association between dietary glycemic load and metabolic syndrome has not yet been found.

Low-Glycemic Index Foods Chart

While it’s unlikely you’ll remember the exact GI for every food, it helps to know whether common foods are low or high on the chart.

[Low-glycemic index foods] have a lower glycemic index because they have more fiber, protein and fat compared to carbohydrates.

Below are several foods that have a low average GI, per research published by the ADA’s Diabetes Care and the Journal of Ethnic Foods.

Food	Average GI
Carrots (and other non-starchy vegetables)	39
Strawberry jam/jelly	49
Legumes and beans	16-32
Apples	44
Avocados	40
Bananas	51
Tomatoes	38

Other common low-GI foods include unrefined grains, peanuts, squash, cauliflower, nuts and seeds.

High-Glycemic Index Foods Chart

Common foods that have a high GI (about 76 and higher) are listed below, with their average GI per research in ADA’s Diabetes Care.

Food	Average GI
White bread	75
Cornflakes (and other common breakfast cereals)	81
White rice	73
Potatoes	78
Rice crackers	87

Other common high-GI foods include cake, pastries, bagels, processed snacks and maple syrup.

How Is Glycemic Index Measured?

A food’s glycemic index number is determined through a series of clinical trials with a small number of human test subjects. In these tests, participants’ blood sugar levels are measured before and after eating a serving of food that equals 50 grams of carbohydrates. For example, if potatoes are being tested, each participant would eat however many potatoes are required to meet 50 grams of carbohydrates.

After consuming the food source, blood glucose levels are measured at intervals of usually 15, 30, 45, 60, 90 and 120 minutes.

These varying blood sugar levels are then graphed. At that point, the area under the blood glucose curve (AUC) is calculated, which represents the rise and fall of blood glucose over the two-hour period, The glycemic index is then determined by dividing the AUC of the food being tested by the AUC of the reference food source, then multiplying by 100.

Limitations of Glycemic Index

Although perhaps a helpful starting point for understanding how certain foods may affect glucose levels, the glycemic index should not be used alone; instead, it should be considered alongside a food’s energy density and macronutrient profile, recommends the ADA.

The GI isn’t a perfect measurement and it faces a few limitations:

Fluctuating numbers. The GI of some foods, including porridge oats, has produced variable results, notes the ADA, suggesting this may be due to differences in cooking methods over the years.

Limited effect. Blood sugar is affected by not only a food’s carbohydrate content, but also by the type of carbohydrate (refined or unrefined) and other foods eaten at the same time.

Individual variability. GI measurement testing in a handful of individuals does not account for the variability across the population, as there are differences in gut microbiome, genetics, metabolic rate, daily activity, stress and medications, experts note.

Inconsistent portion size. A food’s GI is determined based on its serving size that equates to 50 grams of carbohydrates. In reality, most people are likely eating portion sizes that don’t equal the test size, meaning the GI won’t realistically depict the food’s glucose effect.

Preparation variability. Even the way a food is prepared alters its GI. For example, a boiled potato has an average GI of 78, instant mashed potato has a GI of 87 and French fries have a GI of 63, per the ADA’s measurements.

Although GI can be a good starting point, Rand and Jones recommend focusing more on eating well-balanced meals to keep your blood sugar in check. Starting a meal with a salad or vegetables or eating fibers, fats and proteins alongside sugars and starches helps slow down digestion and the absorption of carbs, they say.

Eating balanced meals not only helps regulate blood sugar levels, but can also lower your risk for type 2 diabetes or help manage it in the long term, according to Jones. That way, you can focus on enjoying a wide-ranging, healthy meal instead of committing GI numbers to memory.

For those with diabetes, more care and attention should be paid to total grams of carbohydrates at each meal and snacks, as well as regularity in their meal and snack timing, it is recommended to work with a registered dietitian who is a certified diabetes educator (CDE), who can help you create a plan for the timing and amounts of carbs that should be consumed.

Glycemic index chart

When it comes to how to calculate glycemic index numbers, doctors have measured only certain foods or classes of foods (foods like meats, fats and oil don’t contain carbs).

To determine glycemic index numbers, doctors observe how healthy people’s blood sugar levels change after ingesting carb-containing foods. By measuring subsequent blood sugar levels — and comparing it to a baseline — they can determine where a food falls on a scale of zero to 100, where 100 represents pure glucose and zero is a food with no sugar at all.

Use this glycemic index food chart as a starting point.

Low-glycemic index foods

GI of 55 or less include:

Medium-glycemic index foods

GI of 56-69 include:

High-glycemic index foods

GI of 70 or more include:

Apple
Banana
Barley
Broccoli
Carrots
Cashews
Chickpeas
Dark chocolate
Eggplant
Lemons
Lettuce
Limes
Mango
Oranges
Peanuts
Pears
Peppers

Corn Tortilla
Pasta
Soy Milk
Grapes
Corn
Peas
Most Vegetables
Kidney Beans
Black Beans
Plain yogurt
Skim milk
Strawberries
Tomatoes
Whole milk

Brown rice
Couscous
Pineapple
Popcorn
Potato chips
Soda
Sweet potato
Oatmeal
Raisins
Peach
Sucrose
Short Bread
Pita Bread
Wholemeal bread

Cereal
Cheeseburger
Corn chips
Doughnuts
French fries
Fried chicken
Mashed potatoes
Pizza
Pretzels
Sports drink
White bread
Bagel
Baked Potato
Wheat Bread
White Rice
Rice Milk
Watermelon

The University of Sydney has a useful Glycemic Index Database you can search.

Another useful FoodStruct Glycemic Index Chart you can search

Why calculating the index isn’t exact

Determining the glycemic index ratings for individual foods is an imperfect science. Factors like how food is processed or prepared plays a role.

For example, one study of instant oatmeal shows that it had a glycemic index of 79, which is the high range. Yet steel-cut rolled oats have a glycemic index of 55, which puts it in a low glycemic index.

Different versions of the same food will also vary due to ingredients. For example, yogurt that’s marketed for kids is going to taste delicious because it has a lot of sugar or artificial sweeteners, like high fructose corn syrup — versus plain Greek, regular fat yogurt.

They might have very similar amounts of carbs, but the glycemic index is very different because of the number of proteins and fats and the quality and quantity of the sugar that’s in there.

How much you eat of a certain carb-heavy food can also have an effect. For example, a small sip or two of soda won’t have as big an impact on your body as a large portion of whole-grain rice — even though the latter is generally perceived as healthier.

As with many diets moderation is key, as is striking a balance between eating low and high glycemic index foods.

Food Group	Food	Glycemic Index	Serving Size	Glycemic Load (Per Serving)
Vegetables	Spinach	0	30g (1 cup)	0.0
	Mushrooms	0	70g (1 cup)	0.0
	Green Beans	0	135g (1 cup)	0.0
	Cauliflower	0	100g (1 cup)	0.0
	Celery, raw	0	62g (1 stalk)	0.0
	Cabbage, cooked	0	75g (1/2 cup)	0.0
	Broccoli, cooked	0	78g (1/2 cup)	0.0
	Tomato	38	123g (medium)	1.5
	Frozen Peas	48	72g (1/2 cup)	3.4
	Yams	51	136g (1 cup)	16.8
	Sweet Potatoes	54	133g (1 cup)	12.4
	Yellow Corn	55	166g (1 cup)	61.5
	Potato	104	213g (medium)	36.4
	Potato, baked	111	150g	33.0
	Potato, boiled	82	150g	21.0
	Parsnips	97	78g (1/2 cup)	11.6
	Beets, canned	64	246g (1/2 cup)	9.6
Fruits	Sweet Cherries, raw	22	117g (1 cup)	3.7
	Plum	24	66g (1 fruit)	1.7
	Grapefruit	25	123g (1/2 fruit)	2.8
	Peach	28	98g (medium)	2.2
	Prunes	29	132g (1 cup)	34.2
	Dried Apricots	32	130g (1 cup)	23.0
	Pear	33	166g (medium)	6.9
	Apple, with skin	39	138g (medium)	6.2
	Strawberries	40	152g (1 cup)	3.6
	Grapes	43	92g (1 cup)	6.5
	Pears, canned	44	248g (1 cup)	12.3
	Orange	48	140g (1 fruit)	7.2
	Banana	51	118g (medium)	12.2
	Mangos	51	165g (1 cup)	12.8
	Peaches, canned	52	251g (1 cup)	17.7
	Fruit Cocktail	55	214g (1 cup)	19.8
	Kiwi, with skin	58	76g (1 fruit)	5.2
	Papayas	60	140g (1 cup)	6.6
	Raisins	64	43g (small box)	20.5
	Apricots, canned	64	253g (1 cup)	24.3
	Cantaloupe	65	177g (1 cup)	7.8
	Pineapple	66	155g (1 cup)	11.9
	Watermelon	72	152g (1 cup)	7.2
Legumes	Peanuts	13	146g (1 cup)	1.6
	Soy Beans	20	172 (1 cup)	1.4
	Kidney Beans	27	256g (1 cup)	7.0
	Lentils	29	198g (1 cup)	7.0
	Chickpeas, boiled	31	240g (1 cup)	11.3
	Pinto Beans	39	171g (1 cup)	11.7
	Lima Beans	31	241g (1 cup)	7.4
	Baked Beans	48	254g (1 cup)	18.2
Nuts	Cashews	22	N/A	N/A
	Hazelnuts	0	N/A	N/A
	Almonds	0	N/A	N/A
	Macadamia Nuts	0	N/A	N/A
	Pecans	0	N/A	N/A
	Walnuts	0	N/A	N/A
Dairy	Ice Cream	38	72g (1/2 cup)	6.0
	Low-Fat Ice Cream	47	76g (1/2 cup)	9.4
	Whole Milk	40	244g (1 cup)	4.4
	Plain Yogurt	36	245g (1 cup)	6.1
Beverages	Tomato Juice	38	243g (1 cup)	3.4
	Apple Juice	41	248g (1 cup)	11.9
	Soy Milk	44	245g (1 cup)	4.0
	Grapefruit Juice	48	250g (1 cup)	13.4
	Orange Juice	57	249g (1 cup)	14.25
	Cola	63	370g (12 oz.)	25.2
	Hot Chocolate	51	28g (1 packet)	11.7
	Cranberry Juice	68	253g (1 cup)	24.5
	Gatorade	78	16g (3/4 scoop)	11.7
Candy/Sweets	Peanut M&Ms	33	30g (1 ounce)	5.6
	Strawberry Jam	51	2 tablespoons	10.1
	Jelly Beans	78	1 ounce	22
	Honey	87	2 tablespoons	17.9
	Snickers Bar	68	60g (1/2 bar)	23.0
	Table Sugar	68	2 tablespoons	7.0
Grains	Quinoa	53	150g (1 cup)	13.0
	White Rice	89	150g (1 cup)	43.0
	Brown Rice	50	150g (1 cup)	16.0
	Bulgur	48	150g (1 cup)	12.0
	Couscous	65	150g (1 cup)	9.0
	Pearled Barley	28	150g (1 cup)	12.0
Cereals	Oatmeal	55	250g (1 cup)	13.0
	Muesli	66	30g (1 cup)	16.0
	Bran Cereal	55	30g (1 cup)	12.0
	Puffed Wheat	80	30g (1 cup)	17.0
	Cheerios	74	30g (1 cup)	13.3
	Rice Krispies	82	33g (1.25 cup)	23.0
Baked Goods	Graham Cracker	74	14g (1 squares)	8.1
	Kaiser Roll	73	57g (1 roll)	21.2
	Bagel	72	89g (1/4 in.)	33.0
	Glazed donut	76	75g (large)	24.3
	White Bread	70	25g (1 slice)	8.4
	Wheat Bread	70	28g (1 slice)	7.7
	Banana cake (made with sugar)	47	60g	14
	Banana cake (made without sugar)	55	60g	12
	Sponge cake (plain)	46	63g	17
	Pita bread, white	68	30g	10
	Corn tortilla	52	50g	12
	Wheat tortilla	30	50g	8
	Hamburger bun	61	30g	9
Miscellaneous	Hummus	6	30g	0.0
	Popcorn	55	8g (1 cup)	2.8
	Cheese Pizza	80	100g	22.0

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