SUGiRS, or Sydney University GI Research Service is the official testing facility for the glycemic index and responsible for the database of GI rankings. Located in Sydney, Australia, SUGiRS was established in 1995 to "provide a reliable commercial GI testing laboratory for the local and international food industry." Any food manufactures can pay to have the GI of their product tested, assuming the food contains carbohydrates. Only carbs can be GI tested.
Testing Procedure
Testing for the glycemic index involves a group of at least 10 healthy adults who consume 50 carbohydrate grams worth of the food to be tested -- not 50 g of the food, but whatever amount of food contains 50 g of carbohydrates. Blood sugar levels are checked at set intervals for each test subject. At another time, the same group of test subjects is given 50 g of pure glucose -- to get a set of control measurements. Blood sugar levels are checked at the same timed intervals. The difference between the results of the test food and the glucose control are compared for each individual, then all the individuals scores are averaged to determine the glycemic index score of the test food.
GI and Blood Sugar
What the glycemic index tries to measure is the potential of any carbohydrate to raise your glucose level. The higher a food scores on the GI, the greater the impact on glucose levels. Although the GI may be a useful tool, it is inherently flawed. Fifty grams of carbohydrates is often not the serving size -- and how much of the food you eat affects blood sugar levels. Eating a double or triple portion of a low-GI food may significantly raise blood sugar. And just because a food scores low on the GI doesn't make it "healthy," low in calories or low-fat. Fat as well as fiber can lower a GI score; chocolate bars and ice cream are low-GI foods, while bananas are not.
Glycemic Index vs. Glycemic Load
The glycemic load was developed to try and address some of the concerns about the glycemic index. The GL corrects the GI for portion size. The glycemic load is calculated by multiplying the GI score and the number of carbohydrates in a true serving and then dividing that number by 100. This may give a truer picture of how a food really affects blood sugar. For example, the GI of macaroni and cheese is 64, but the GL is 32. But the GI for carrots is 47 and the GL is 3.
GI and Weight Loss
The GI and GL scores of foods may still be a useful tool for weight loss. You need to use the GI or GL as a guide, but still choose nutrient dense carbs low in sugar and starch. Fruits, vegetables, beans and whole grains can help you feel full faster and stay satisfied longer, leading to an overall reduction in caloric intake. Weight loss is a matter of consuming fewer calories than you need, creating a calorie deficit.
