Glycemic index is a way of measuring how high and how fast our blood sugar rises after we eat carbohydrate – containing foods such as bread, pasta, vegetables, fruits, grains, baked goods, etc. After we consume these foods they are broken down into glucose that ends up in our blood stream. All carbohydrates we eat raise our blood sugar to some extend. Proteins and fats don’t raise blood sugar too much so they don’t have a glycemic index.
Some foods are digested and absorbed very quickly causing a spike in blood sugar. These foods have a higher glycemic index. Other foods are digested and absorbed slowly. They don’t spike our blood sugar; instead they gradually release energy keeping us full longer. These foods have a lower glycemic index.
Glycemic index ranges from 1 to 100, with glucose having the glycemic index of 100.
According to their GI rating, carbohydrate – containing foods are placed into 3 categories:
- Low-glycemic foods with GI ranging from 0 to 55;
- Medium-glycemic foods with GI ranging from 56 to 69;
- High-glycemic foods with GI ranging from 70 to 100.
Here are examples of some common foods and their GI ratings:
- Slow-cooking oatmeal 54
- Banana 52
- Green peas 48
- Carrots, raw 47
- Orange 42
- Apple 40
- Dried beans 25
- Table sugar 68
- Taco shells 68
- Croissant 67
- Instant oatmeal 65
- Rice, white or brown 60
- Bran muffin 60
- Muffin, blueberry 59
- Glucose 100
- French bread 95
- Potato, baked 85
- Potato, mashed 85
- Corn flakes 81
- Wheat bread 70
- White bread 70
The concept of glycemic index was developed in the early 80s by Dr. David J. Jenkins and his colleagues at the University of Toronto. In the beginning, glycemic index was only considered important for people with diabetes because low GI foods help diabetics keep their blood sugar levels in the healthy range. Recently however, nutrition experts started to understand that low-glycemic way of eating also helps people lose weight and keep it off without dieting, deprivation, and counting calories and is an overall healthy approach to eating.
Glycemic index can be confusing at times because it doesn’t reflect the amount of actual carbohydrate in a particular food. To help clarify this confusion, another index of the blood-glucose-raising potential of carbohydrate-containing foods has been developed – it’s called glycemic load.
Glycemic load is calculated by multiplying the glycemic index of a particular food by the grams of carbohydrate in a specific amount of food; the result is then divided by 100. Glycemic load formula looks like this:
GL (glycemic load) =(GI (glycemic index) X the amount of carbohydrate) / 100
For example, an apple has a GI of 40 and contains 15 grams of carbohydrates. So we will calculate the GL of an apple as follows: 40 X 15 / 100 = 6 g. Glycemic load of an apple is 6.
Glycemic load less that 10 is considerate to be low; GL from 10 to 20 is considerate to be moderate or medium; and GL above 20 is considerate to be high.
Glycemic load helps us understand why some fruits with high glycemic index are still good for us and won’t spike out blood sugar. For example, a watermelon with the glycemic index of 72 and a cantaloupe with the glycemic index of 65 have a low glycemic load of 4.
On the other hand, fruit juices spike blood sugar despite the fact that they might have the same glycemic index as the fruit they are made of. For example, fresh apple and apple juice have the same glycemic index of 40. But fresh apple has a glycemic load of 6 and apple juice has a glycemic load of 12 which means that apple juice will have twice the metabolic effect of an apple.
Both, glycemic index and glycemic load are important principles to understand if you want to learn how to keep your blood sugar stable throughout the day and / or are interested to know how low-glycemic eating can help you lose weight and keep it off.
Considering the obesity and diabetes epidemic that is sweeping all developed nations around the globe; considering the amounts of packaged foods and sugary drinks millions of people consume every day; in my opinion, everyone can benefit from education about low glycemic eating and keeping the blood sugar stable. Regardless of whether you want/need to eat gluten-free, dairy free, vegetarian, vegan, or paleo, glycemic control should be included in your daily meal planning and preparation.