Introduction

One of the most important concepts to understand when you are a diabetic is the concept of glycemic index (GI), the measure of how quickly carbohydrate foods affect blood glucose levels. Since the condition of diabetes impairs the body's ability to effectively maintain proper levels of glucose in the blood it is important to make informed food choices that can reduce the speed at which carbohydrates from a meal reach the bloodstream as glucose and the total amount of glucose reaching the bloodstream. In this article we will briefly review the fundamentals of carbohydrate structure and the glycemic index of different foods. You may be in for some surprises.

As you are probably aware the three major food groups (macronutrients) include proteins, fats and carbohydrates. While fats and proteins are essential for growth and repair of tissue and membranes and their general maintenance it is the carbohydrates that provide us with most of the fuel that we burn for energy. Carbohydrates are made up of carbon, hydrogen and oxygen. These molecules are arranged in ring structures that can be linked together to form larger molecules. Carbohydrates can be as simple as single-ringed monosaccharides such as glucose, fructose (fruit sugars) and galactose (a milk sugar). They may also appear as two-ringed molecules, called disaccharides, including maltose (glucose plus glucose), sucrose (glucose plus fructose) and lactose (glucose plus galactose). Neither plants nor animals store energy in the form of these sugars as this would lead to an osmotic imbalance (the cells would take up water and burst). Therefore, sugars are converted to larger molecules for storage. In plants these are called starches, the two most common being amylopectin and amylose. Amylose is made up of glucose rings strung together in a long strand. Amylopectin is similar except it has many side branches. This difference is important because it affects their rate of enzymatic breakdown during digestion. Because of the many side chains amylopectin offers more sites for enzymes to work and is broken down more rapidly.

The Glycemic Index

How is the glycemic index (GI) actually determined? Typically the reference point against which all other foods are measured is pure glucose since that is the final product of carbohydrate digestion that enters the blood. The rate at which pure glucose enters the blood is designated a GI value of 100, all other foods being relative to this glucose standard. An important thing to keep in mind is that the GI reflects the rate or speed that different foods appear as glucose in the blood. We also need to consider the total glucose load which that food will deliver to the blood stream which is a function of the food amount and the percent carbohydrate content of the food. It is the large carbohydrate loads with high GI values that will deliver large amounts of glucose into the blood in a very short time. By regularly consuming foods geared towards a low average GI and low total carbohydrate, it should be possible to improve glycemic management in diabetes.

The GI is determined for a single type of food but in the real world the typical meal is a combination of foods composed of not just carbohydrates but also fat and protein along with fiber and micronutrients. The interaction of these foods in the digestive tract can alter the rate of digestion and absorption. The GI is still a valuable guide, however, when trying to estimate and reduce the GI of a whole meal, which should be the goal of all diabetics.

Sample calculation: For the sake of simplicity let's say that a breakfast meal contained 100 grams of carbohydrate. This included white toast (2 slices at 13 grams each = 26 grams), hash brown potatoes (54 grams), and half a grapefruit (20 grams). First calculate the percentage each contributes to the total carbohydrate. Then multiply that by the glycemic index of each type. Then add these three numbers together. You should try doing a few of these calculations since many food combinations appear in your diet repeatedly meaning you don't have to do calculations at every meal. You will learn to identify various food combinations and amounts as you would a spicy dish (ie. mild, medium, hot and very hot) in terms of the GI.

Sample Calculation

SAMPLE CALC HERE...