Learn about the Glycemic Index and the Rating of Common Carbohydrate Foods

What is the Glycemic Index

• The glycemic index ranks foods on how they affect our blood glucose levels. This index measures how much your blood glucose increases in the two or three hours after eating.
• The glycemic index is about foods high in carbohydrates. Foods high in fat or protein don't cause your blood glucose level to rise much.
• The glycemic index is about the quality of the carbohydrates, not the quantity. But not all carbohydrates act the same. Some are quickly broken down in the intestine, causing the blood glucose level to rise rapidly. These carbohydrates have a high glycemic index.

How is it Used?

Before the development of the glycemic index beginning in 1981, scientists assumed that our bodies absorbed and digested simple sugars quickly, producing rapid increases in our blood glucose level. This was the basis of the advice to avoid sugar, a proscription recently relaxed by the American Diabetes Association and others.

Now we know that simple sugars don't make your blood glucose rise any more rapidly than some complex carbohydrates do. Of course, simple sugars are simply empty calories, and still should be minimized for that reason.

When you make use of the glycemic index to prepare healthy meals, it helps to keep your blood glucose levels under control. This is especially important for people with diabetes, although athletes and people who are overweight also stand to benefit from knowing about this relatively new concept in good nutrition.
Recent studies of large numbers of people with diabetes show that those who keep their blood glucose under tight control best avoid the complications that this disease can lead to.

The Numbers
Many of the glycemic index results have been surprises. For example, baked potatoes have a glycemic index considerably higher than that of table sugar.  Here are the basic breakdowns of the glycemic scale.

• Low Glycemic Index food (less than 55) 
• Foods with GI index between 55 and 70 are consider intermediate
• High Glycemic Index food GI (more than 70)

GI Food Chart | Low GI Foods | Medium GI Foods | High GI Foods

Notes: *high in empty calories **low-calorie and nutritious foods 

Notes:  *high in empty calories **low-calorie and nutritious foods

What is the Glycemic Load and How is it Used?

The glycemic load (GL) is a ranking system for carbohydrate content in food portions based on their glycemic index (GI) and the portion size.

The usefulness of glycemic load is based on the idea that a high glycemic index food consumed in small quantities would give the same effect as larger quantities of a low glycemic index food on blood sugar. For example, white rice is somewhat high GI, so eating 50g of white rice at one sitting would give a particular glucose curve in the blood, while 25g would give the same curve but half the height. Since the peak height is probably the most important parameter, multiplying the amount of carbohydrates in a food serving by the glycemic index gives an idea of how much effect an actual portion of food has on blood sugar level.

Glycemic load for a single serving of a food can be calculated as the quantity (in grams) of its carbohydrate content, multiplied by its GI, and divided by 100. For example, a 100g slice serving of watermelon with a GI of 72 and a carbohydrate content of 5g (it contains a lot of water) makes the calculation 5*0.72=3.6, so the GL is 3.6. A food with a GI of 100 and a carbohydrate content of 10g has a GL of 10 (10*1=10), while a food with 100g carbohydrate and a GI of just 10 also has a GL of 10 (100*0.1=10).