The Glycemic Index
The glycemic index ranks foods containing carbohydrates based on how quickly the carbohydrates raise blood sugar levels, according to Maria Collazo-Clavell, M.D., an advisor to the Mayo Clinic. As the body digests food, it converts carbohydrates into glucose (the glycemic response). The more quickly a particular food is digested, the quicker the conversion to glucose, causing a spike in blood glucose levels. The index rates foods on a 100-point scale, with higher scores indicating foods that cause the quickest increases in glucose. The scale was derived from experiments feeding volunteers controlled portions various foods and measuring their blood glucose levels. Foods on the index are compared against pure glucose or one slice of white bread, each of which have a glycemic index value of 100, according to Arthur Agatston, MD, a cardiologist and author of the "South Beach Diet."
Glycemic Load
Glycemic index values only provide a comparison of how quickly the body converts a specific food into glucose. The index does not account for portion size, which is an equally important component in raising blood glucose levels, according to Agatston. Glycemic load is the combination of the glycemic index value and the total portion size. To determine the glycemic load, divide the glycemic index value by 100, then multiply that number by the net carbohydrates (total carbohydrates minus the dietary fiber). The resulting value represents the stress to the pancreas, which produces insulin, from the carbohydrates in a specific food or portion. The higher the glycemic load, the harder the pancreas must work to produce more insulin to regulate the excess glucose.
Glycemic Index and Weight Loss
Excess blood glucose triggers the pancreas to produce more insulin to reduce glucose levels, according to NutritionData.com. Insulin converts the glucose to body fat to store for later use. When glucose levels fall, excess insulin remains in circulation, causing food cravings. The glycemic index attempts to keep blood glucose at a steady level, limiting cravings and feelings of hunger. Foods with a low glycemic index value are digested more slowly than those with a higher value. This means carbohydrates are released into the body more slowly, blood glucose spikes are limited, cravings are reduced and hunger pangs are delayed. Agatston notes foods lower on the glycemic index scale tend to be high in unrefined carbohydrates, such as whole grains, nuts, and fresh fruits and vegetables. The glycemic index and glycemic load can be important weight loss tools, but remember many factors affect the glycemic index, according to Collazo-Clavell. The way in which food is prepared, the other foods eaten during the meal, and the total fat, protein and fiber content all affect how quickly a particular food is digested.
References
- Mayo Clinic: Is the Glycemic Index Diet Useful for People With Diabetes?
- NutritionData.com: Glycemic Index
- "The South Beach Diet: Good Fats, Good Carbs Guide;" Arthur Agatston, MD; 2004
