What is Glycemic Index and Glycemic Load?
Many of our patients often bring up the topic of Glycemic Index (GI) when asking about which foods they should choose to eat, especially those concerned with limiting their sugar or refined carbohydrate intake. Before we get into this discussion, let’s start with some basics.
A macronutrient is defined as a carbohydrate, fat, or protein. These are the basic building blocks of our nutrition and most people are familiar with these categories. Obviously, many foods we eat are a combination of more than one macronutrient (for example, piece of cake which contains all three). Most whole foods that are minimally processed, such as an apple, contains mostly carbohydrates, but a whole food such as milk contains all three. For the purpose of Glycemic Index and Glycemic Load (GL) we will concentrate on carbohydrates.
Carbohydrates come in simple forms such as sugars and in complex forms such as starches and fiber. The body breaks down most sugars and starches into glucose, a simple sugar that the body can use to feed its cells. Complex carbohydrates are derived from plants and typically take longer to break down than simple carbohydrates. They are chemically made up of carbon, hydrogen, and oxygen. The name CARB-o-Hydrate comes from the fact that the amount of carbon, hydrogen, and oxygen they contain are in proportion to create water. A simple carbohydrate would be high fructose corn syrup or white table sugar, commonly found in most processed and prepared foods. A complex carbohydrate would be broccoli, a delicious and nutritious whole food.
Glycemic Index Defined
The Glycemic Index is a ranking of how much a carbohydrate containing food will raise your blood sugar and insulin levels, based on a scale of 0 to 100, with the higher number indicating a greater rise in blood sugar. Generally the more processed and refined the food is, the higher the Glycemic Index will be. This simple chart has some examples of where commonly eaten foods fall on the list.
A more specific ranking system for carbohydrate-containing foods is the Glycemic Load, which factors in the serving size of the food. You can determine the Glycemic Load of a food by multiplying its Glycemic Index by the amount of carbohydrates it contains.
For example, carrots have a high Glycemic Index of 47, but you have to eat a pound and a half of them for there to be a steep rise in blood sugar. Even a rabbit won’t eat that many carrots in one sitting! Because carrots have a high Glycemic Index number, it seems like they are a food to avoid, whereas in fact they are full of excellent nutrients and, when eaten in normal proportions, are unlikely to cause a dramatic influx of blood sugar levels. The Glycemic Load provides a more practical way of evaluating the effect of carbohydrates on blood sugar by combining both quantity and quality of carbohydrate into one number. According to the GL system, therefore, carrots are given a relatively low rating of three. (http://www.calorieking.com/learnabouts/The-Glycemic-Index-The-Glycemic-Load_OTI2.html) So, when choosing your carbs, try to choose foods with a low Glycemic Load, even if you might have been told that same food has a high Glycemic Index. When in doubt, foods that are eaten in the same form that they were grown typically are safe to eat.