A low glycemic index diet helps keep levels of blood sugar and insulin low and helps prevent and treat diabetes, cancer and cardiovascular disease, according to the Florida State University student health center. Glycemic load measures not only the glycemic index based on a standard amount of carbohydrate but also takes into account the specific amount of carbohydrate contained in one serving of the food item. Neither considers calories or nutrients other than carbohydrate.
History
Intensive research in recent years provides some scientific validity to the ideas of glycemic index and glycemic load, according to Sareen Gropper, Jack Smith and James Groff in "Advanced Nutrition and Human Metabolism." Some studies found the GI helpful in meal planning for persons with diabetes but others found it too complicated and impractical to follow. It is still somewhat controversial as a medical nutrition therapy, according to Eleanor Whitney and Sharon Rolfes in "Understanding Nutrition."
Glycemic Effect
Glycemic effect refers to how quickly glucose is absorbed from the food you eat, as well as how high blood glucose rises and how quickly it returns to normal, according to "Understanding Nutrition." A food with a low glycemic effect absorbs slowly and causes a moderate rise in blood glucose, which soon returns to normal. A food with a high glycemic effect absorbs very quickly causing a sudden upward surge in blood glucose that may remain high for an extended time or may cause the body to overreact and plunge glucose too low.
Glycemic Index
The glycemic index assigns a numerical ranking to foods that contain carbohydrate to enable a quantitative comparison based on their effect on blood glucose levels. The glycemic index is the increase in blood glucose level during the two hours following consumption of a defined amount, usually 50 g, of carbohydrate in a food item compared with the rise caused by the same amount of carbohydrate in a standard food, usually white bread, which is assigned a GI of 100, according to "Advanced Nutrition and Human Metabolism."
Glycemic Load
Meals typically consist of a number of food items rather than a single food and servings of various foods typically do not each consist of exactly 50 g of carbohydrate. To address this concern the glycemic load considers both the actual amount of carbohydrate in a serving and the glycemic index of that carbohydrate. The glycemic load of a meal is the sum of the glycemic load of each food item consumed.
Relation
Multiply the glycemic index of a food by the number of grams of carbohydrate in a serving and divide the total by 100 to get the glycemic load of a serving of that food, according to the Linus Pauling Institute. For example, a medium size carrot has a glycemic index of 71 and contains 8 g of carbohydrate. The carrot's glycemic load is 71 times 8, or 568, divided by 100 equals 5.68, rounded to 6.
Considerations
The glycemic response to a meal is somewhat complicated and not always intuitive. A low GI food may not be the healthiest choice. A candy bar high in calories and low in nutrients may have a low GI and some ice creams may have a lower GI than potatoes. The way foods are processed, cooked and consumed together influences the glycemic effect of the meal. Food package labels seldom specify GI ranking or glycemic load and many foods are not yet ranked, according to MayoClinic.com.
References
- Florida State University: Thagard Student Health Center: Glycemic Index
- "Advanced Nutrition and Human Metabolism"; Sareen Gropper, Jack L. Smith and James L. Groff; (2009)
- "Understanding Nutrition, Ninth Edition"; Eleanor Noss Whitney and Sharon Rady Rolfes; (2002)
- Linus Pauling Institute: Glycemic Index and Glycemic Load
- MayoClinic.com: Is the glycemic index diet useful for people with diabetes?
