The Glycemic Index Diet for Dummies (5 page)
GI of 55 or less = low
GI 56 to 69 = medium
GI of 70 or more = high
Introducing the glycemic load
Putting a numerical value on how various carbohydrate-containing foods affect blood sugar levels — the glycemic index — is great. However, the glycemic index is calculated using a standard weight of food, usually 50 grams. A food's glycemic index actually changes based on the amount of it that you eat, which is why a standard weight amount is always used when calculating the glycemic index. In real life, you don't always eat a standard amount of food. Sometimes you may eat two bowls of cereal at breakfast; other times you may eat one. Occasionally you want second helpings of pasta or an extra roll at dinner. You know what it's like.
The glycemic index is calculated not only for a specific weight of food but also for eating just that one food. That's great for researching how one particular food affects blood sugar levels, but what happens when you eat more than one food at a time, such as a peanut butter sandwich with a glass of milk and an apple?
This is where a little something called the glycemic load becomes important. I cover glycemic load extensively in Chapter 4, but here are the basics: The
glycemic load
applies the glycemic index to the amount of food you're actually going to eat, or to the total amount of carbohydrate-containing foods in a meal or snack. To calculate the glycemic load (GL), multiply the glycemic index (GI) of a food by the amount of carbohydrates in the food and then divide by 100. For example, 1 cup of watermelon has a GI of 72 and contains 10 grams of carbohydrates. 72
×
10 = 720, and 720 ÷ 100 = 7, the glycemic load of 1 cup of watermelon. If you eat two cups of watermelon, use this calculation: 72
×
20 = 1,440; 1,440 ÷ 100 = a GL of 14.
What if you eat a turkey sandwich with two pieces of bread and drink one cup of fat-free milk? A slice of white bread has a GI of 70, and each slice contains 15 grams of carbohydrates. One cup of fat-free milk has a GI of 32 and contains 13 grams of carbohydrates. The GL for this meal is 44 (70 + 32 = 102; 102
×
43 = 4,386; 4,386 ÷ 100 = GL of 44).
Just like the glycemic index, glycemic load levels are divided into three categories:
GL of 10 or less = low
GL of 11 to 19 = medium
GL of 20 or more = high
A basic guideline is to keep your total daily glycemic load under 100. In this case, if you're eating three meals per day and each meal has about the same glycemic load, you'll go over the ideal total maximum of 100. To prevent yourself from going over, choose to balance a higher-glycemic meal with a lower-glycemic one or swap out a higher-glycemic food for lower-glycemic one to reduce a meal's overall glycemic load.
A brief history of the glycemic index
In 1981, scientists at the University of Toronto conducted groundbreaking research on the blood sugar effects of 62 different types of foods containing carbohydrates: vegetables, fruit, milk, legumes, and breakfast cereals. They found significant differences between different types of carbohydrate-containing foods, which led them to suggest using the glycemic index as a way to classify carbohydrate foods by how quickly they raise blood sugar levels. The glycemic index was first used as a way of helping people with diabetes control their blood sugar levels, moving beyond simple carbohydrate counting. Over the years and with more research, the glycemic index has become an important nutrition tool for several other chronic conditions, including Polycystic Ovary Syndrome (PCOS), metabolic syndrome, and diabetes.
Jennie Brand Miller, of the University of Sydney's Human Nutrition Unit, is one of the recognized leaders in glycemic index research. She's the lead author of the authoritative
International Tables of Glycemic Index
published by the
American Journal of Clinical Nutrition.
Her group continues to test the glycemic index of a wide variety of different foods so that consumers, health professionals, and scientists can know exactly how different foods influence blood sugar.Australia and Canada continue to be leaders in testing large numbers of foods to help consumers more easily choose low-glycemic foods. Australia started the GI Symbol Program in 2002 to clearly identify proven low-glycemic foods. Canada, Australia, and the United Kingdom have approved the GI Symbol for use on food labels, making it easy to find low-glycemic foods in these countries. The United States has adopted a seal from an accredited testing organization; food companies can have their foods tested by the organization and can use the Low Glycemic Seal if their foods pass the test. For more information on this seal program, head to Chapter 10.
