How is this number determined? Glucose (sugar) is assigned a Glycemic Index of 100. Various foods are tested in sample sizes of 50 grams of carbohydrates against 50 grams of glucose and the degree to which blood sugar is raised is calculated. For example, white bread is converted very quickly into sugar and is classified as having a high Glycemic Index while most vegetables have a very small effect on blood sugar levels and have a low Glycemic Index.
What is wrong with this system? Realistic serving sizes are not taken into account with the Glycemic Index. Most vegetables and fruits are not high in carbohydrates and it is unlikely that somebody would consume 50 grams of one vegetable all at once. In addition, foods are rarely eaten individually; they are usually eaten in combinations which affect how quickly blood sugar is raised. Consuming protein and fats with high carbohydrate containing foods tends to lower the Glycemic Index of a meal. Also, the technique in which a food is cooked (baked vs. boiled), the specific variety of food (golden delicious apple vs. fuji), the ripeness of a food, and even the temperature of the food can drastically change the Glycemic Index.
The Glycemic Load is somewhat of an improvement over the Glycemic Index, however because it is based on the Glycemic Index it has many of the same limitations. The Glycemic Load takes the Glycemic Index and multiplies it by the number of carbohydrates in that food. This is a more sensible approach because the calories (quantity) of food is taken into account. This lowers the Glycemic value of most fruits and vegetables since they are generally lower in calories.
If you search the web for lists of foods and their Glycemic Index and Glycemic Load, do not be surprised to find quite a variation and inconsistency depending on the source. This is due to differences in laboratories and individual digestion.
Bottom line: While the basic guidelines of the Glycemic Index emphasize eating fruits, vegetables, beans, and whole grains, do not get too hung up on specific number assignments. For instance, just because pineapple and watermelon have higher Glycemic Indexes than an apple, does not mean that you should avoid eating these very nutritious fruits. Be careful not to use the Glycemic Index or the Glycemic Load of a food to decide whether or not it is good for you. It is far too complicated and unscientific. The fiber content, phytochemicals, and vitamins and minerals in a food are a much better determinant of whether or not a food is a healthy choice. Stick to eating mainly whole foods and high fiber plant foods while avoiding highly processed sugars and starches to maintain healthy blood sugar levels and increased satiety. You do not need charts and numbers to choose nutritious foods; just your common sense.
Corinne Goff is a Registered Dietitian who is absolutely passionate about food, health, and nutrition. Corinne has a BA in Psychology from Salve Regina University and a BS in Nutrition from the University of Rhode Island. As a nutritionist, her objective is to help people reach their health goals by offering a personalized holistic approach to wellness that incorporates natural foods and lifestyle changes. She works together with her clients to develop daily improvements that they feel comfortable with and that are realistic. She believes that the focus on wholesome, nutrient-rich, real food, is the greatest possible way to become healthier, have more energy, decrease chances of chronic disease, and feel your best. For more information, please visit her website at RI Nutrition Housecalls.com.