Glycemic Load and Glycemic Index


Understanding how a food will affect your blood sugar level is much more difficult than just reading the nutrition facts label. Different types of carbohydrates and the amount of fiber in a food all affect the body in different ways, even though the actual amount of carbohydrates may be the same.

The glycemic index (GI) is a measure of carbohydrate quality based on their immediate effect on blood sugar levels. The higher the glycemic index value, the faster and stronger the food affects your blood sugar and insulin levels. The standard nutrition facts label is misleading because it assumes that all starchy foods produce the same effect on blood sugar levels.

The glycemic index of a food is measured by comparing a volunteer's blood sugar levels after consuming 50 grams of that food to their blood sugar levels after consuming 50 grams of pure glucose (the reference level, which equals 100). This is done several times on several different volunteers in order to come up with an average measurement for that food.

High GI = 70 or higher
Intermediate GI = 56-69
Low GI = 0-55

Examples:
Sticky White Rice has a GI of 87
Spaghetti has a GI of 42
Apples have a GI of 40
Almonds have a GI of 0

The GI value of a food is only one piece of the puzzle. The other piece is the amount of carbohydrate in that food (found on the nutrition facts label). This is where the glycemic load (GL) comes in handy.

Glycemic Load= (GI value x available carbohydrates per serving)/100

This better reflects a food's affect on your body than either the amount of carbohydrate or the glycemic index alone. Because GI is based on 50 grams of a certain food, and 50 grams is not necessarily a reasonable serving size, GL ranks according to a standard serving size of  that food. This is also where fiber plays a role, because the amount of fiber counteracts some of the carbohydrates, so "available carbohydrates" = total carbohydrates minus fiber.

Examples:
1 cup cooked sticky white rice has a GL of 24
1 cup cooked spaghetti has a GL of 20
1 apple has a GL of 6
a handful of almonds have a GL of 0

My goal is to be able to determine the GL of my recipes so you can better understand how they might affect your blood sugar levels. This will be a work in progress, and take a lot of math, so we'll see. However, please understand that I am not a doctor, and I'm just experimenting. Also, foods affect every body differently, and there is some variation, so always take GL measurements with a grain of salt. I will be getting my GI measurements from www.glycemicindex.com, the official index. However, there are no GI ratings for most flours because volunteers have to eat the test food, and most people aren't interested in eating 50 grams of dry flour. I give flours an approximate GI value based on the values of other foods made with it. For example, white bread has a GI of 71, so I give white flour a GI of 71.

The Glycemic Index and Sports Performance

Blood sugar levels affect the fuel and energy available to muscles. There are times when low-GI foods provide an advantage to athletes (or anybody who exercises) and times when high-GI foods are better. When exercising at a high intensity, your muscles rely on glucose for fuel.

Low-GI foods have been proven to extend endurance when eaten alone one to two hours before prolonged strenuous exercise (more than 65 percent of maximum capacity for longer than ninety minutes). They are best eaten about two hours before the big event - so that the meal will have left the stomach but will remain in the small intestine, slowly releasing glucose energy for hours afterwards. Low-GI foods increase endurance and prolong the time before exhaustion hits.

Scientific evidence indicates that there are times when high-GI foods are preferable. This includes during an athletic event (especially if it lasts longer than ninety minutes), after the event, and after normal training sessions. In general, a diet rich in carbohydrates is ideal for athletes, because they maximize muscle glycogen storage and increase endurance.

Brand-Miller, Jennie, Thomas M.S. Wolever, Kaye Foster-Powell, and Stephen Colagiuri. The New Glucose Revolution; The Authoritative Guide to The Glycemic Index. New York: Marlowe & Company, 2003
Willett, M.D. Walter C. (2001). Eat, Drink, and Be Healthy: The Harvard Medical School Guide to Healthy Eating. New York, NY: Fireside

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