The glycemic load, or GL, ranks carbohydrate-rich foods based on how much an average serving of that food will raise blood sugar levels. The ranking of a particular food is mathematically derived from its glycemic index, or GI, and the number of carbohydrates, in grams, in an average serving of that food. Glycemic load values are used for meal planning by diabetics and in weight management.
Glycemic Load
Created in 1997 by Dr. Walter Willett and his associates at the Harvard School of Public Health, the glycemic load ranking of a food gives information about how that food will affect both blood sugar and insulin. It is used to predict how much blood glucose levels will rise and the resultant insulin demand that is produced by eating an average portion of the particular food. The calculation of a food's GL is done by dividing its glycemic index by 100 then multiplying that number by its net carbs, or the grams of total carbohydrates minus the grams of dietary fiber. The formula is: GL = GI/100 x Net Carbs.
Glycemic Index
The glycemic index is a system of numerically ranking carbohydrate foods based on how much each food raises blood glucose levels. Using pure glucose as a reference point, It assigns each carbohydrate food a ranking from 0 to 100 with foods that cause the most rapid rise having the higher numbers. The GI, which evaluates the quality, not quantity, of a carbohydrate, measures how rapidly a carbohydrate food is digested, converted into glucose, and then impacts blood glucose. When carbohydrates break down into glucose during digestion they cause a temporary spike in blood sugar levels. A high GI food, like white bread which is digested quickly, creates a rapid spike then a drop in blood sugar while a low GI food, like whole oats which are digested more slowly, produces a lower and slower change in blood sugar. .
Glycemic Load Vs. Glycemic Index
The glycemic index ranks foods that contain equal amounts of carbohydrate by their predicted effect on blood sugar. The glycemic load also evaluates the impact of carbohydrates but gives a broader picture of their impact on blood sugar. The GI value indicates how quickly a specific carbohydrate converts to sugar but doesn't take into consideration the amount of that carbohydrate in a serving of a food. It is necessary to know both to predict how an average serving of food will impact blood sugar. This is what the glycemic load is designed to do. For instance, the carbohydrate in watermelon has a high GI of about 72. However, there is not a lot of it in a serving of watermelon, so watermelon's glycemic load is relatively low. According to the calculations from the University of Sydney's Human Nutrition Unit, a 120g serving of watermelon has 6g of available carbohydrate per serving, so its GL is low: 72/100 x 6=4.32, which is rounded to 4.
Interpretation
A food with a lower Glycemic
lLoad or glycemic Index has a lesser impact on blood sugar and insulin levels than a food with a higher ranking. In the glycemic index ranking system, low GI foods are ranked 55 or under, moderate GI foods rank 56-69, and high GI foods are ranked 70 and above. In the glycemic load system, a glycemic load of 10 or less is low, a glycemic load of 11 to 19 is medium, and a glycemic load of 20 or more is high. Foods with a low GL almost always have a low GI. Intermediate or high GL foods can have anywhere from a low to a high GI.
Significance
The body's glycemic response depends on the total amount of carbohydrate food consumed and the type of carbohydrate in that food. This is why the glycemic load is considered to be an improvement on the glycemic index. Because the glycemic load is a relative indicator of how much an average serving of food will probably raise blood sugar levels, it is considered a practical application of the glycemic index. As an example, although most candy has a relatively high GI, eating just a small piece will likely produce only a small glycemic response, a measure of food's ability to raise blood sugar. The same thing is true for popcorn. Although 2 cups of popcorn have a GI of 72, the same serving has a GL of 10. It is possible to control the body's glycemic response by restricting carbohydrate intake and/or by eating foods with a low glycemic index and load. Because of this, meals of low glycemic load foods are often recommended to help people manage their diabetes and for weight control..
