The glycemic index (GI)is a scientific approach to assess how the carbohydrates in foods affect blood glucose, or blood sugar, levels. It takes the understanding of how much a particular food raises blood sugar to a deeper level, building upon the well-known fact that all carbohydrates raise blood sugar.

The glycemic index assesses foods on a scale of 0 to 100, determining their ability to raise blood sugar levels rapidly. Foods with a higher number cause a more rapid increase in blood sugar, while foods with a lower number have a less pronounced effect on blood sugar levels.

How To Measure Glycemic Index

To determine the glycemic index of a food, a specific weight of the test food (usually 50 grams, which is about 4 tablespoons of sugar) is fed to at least ten healthy volunteers. The volunteers’ blood sugar levels are measured prior to eating and at 15 to 30-minute intervals for two hours, resulting in a blood sugar response curve. 

The food’s blood sugar response is then compared to that of a control food, typically glucose or table sugar, which is assigned a value of 100. The individual responses of each test subject are averaged to calculate the glycemic index number for the food. 

Related: Glycemic Index and Glycemic Load: Meaning and Benefits

Categories of GI

The categorization of foods into low, medium, or high glycemic foods occurs, and they are ranked on a scale of 0–100.

Here are the three categories:

Low= GI of 55 or less

Medium = GI 56 to 69

High = GI of 70 or more

High glycemic index (GI) foods are those that contain easily digestible and metabolizable carbohydrates. Whereas, low GI foods contain slowly digestible carbohydrates that result in a reduced glucose response after a meal.

Related: Myths about Glycemic Index

Glycemic Index of Common Foods

Low-GI Foods (55 or Less)
Foods	GI
Apple	36
Apple juice	41
Banana	51
Barley	28
Carrots, boiled	39
Chapatti	52
Chickpeas	28
Chocolate	40
Dates	42
Ice cream	51
Kidney beans	24
Lentils	32
Mango	51
Orange	43
Orange juice	50
Peaches, canned	43
Plantain	55
Rice noodles	53
Rolled oats	55
Skim milk	37
Soya beans	16
Soy milk	34
Spaghetti, white	49
Spaghetti, whole grain	48
Specialty grain bread	53
Strawberry jam	49
Sweet corn	52
Taro, boiled	53
Udon noodles	55
Vegetable soup	48
Whole milk	39
Yogurt, fruit	41

Medium-GI Foods (56 to 69)
Foods	GI
Brown rice, boiled	68
Couscous	65
French fries	63
Millet porridge	67
Muesli	57
Pineapple	59
Popcorn	65
Potato chips	56
Pumpkin, boiled	64
Soda, non-diet	59
Sweet potato, boiled	63
Wheat flake biscuits cereal	69
Wheat roti	62

High-GI Foods (70 to 100)
Foods	GI
Cornflakes	81
Instant oatmeal	79
Potato, boiled	78
Potatoes, instant mashed	87
Rice milk	86
Rice porridge	78
Rice crackers	87
Unleavened wheat bread	70
Watermelon	76
White rice, boiled	73
White bread (wheat)	75
Whole wheat bread	74

GI values of foods can be found on the University of Sydney’s GI website

References

1. Raffetto, M. (2014). Glycemic index diet for dummies. Hoboken, NJ: John Wiley & Sons.
2. Barclay, A., & Group, G. (2023, March 01). Alan Barclay. Retrieved March 13, 2023, from https://glycemicindex.com/
3. Glycemic index and Glycemic Load. (2023, January 03). Retrieved March 13, 2023, from https://lpi.oregonstate.edu/mic/food-beverages/glycemic-index-glycemic-load
4. Miller, B. J. (2010). The low GI handbook: The New Glucose Revolution Guide to the long-term health benefits of low GI eating. Cambridge: Da Capo Press.
5. https://www.verywellhealth.com/glycemic-index-chart-for-common-foods-1087476