A glycemic impact diet is based on calculating the predicted impact of carbohydrates on blood glucose levels. Foods are then placed in one of three categories — low, medium, or high GL. GL stands for glycemic load. Foods can carry a rating between 0 and 100, with lower ratings having lesser blood glucose impact.
Calculating glycemic load is a four-step process. The first involves using a glycemic index to find the value for a specific food. Usually, Internet listings can be searched by food name, while print resources tend to be published alphabetically. Index numbers were designed by Dr. David Jenkins of the University of Toronto in the early 1980s. A food's index number is multiplied by total carbohydrates per serving, and then divided by 100 to calculate glycemic load. For instance, a food with a glycemic index of 50 and total carbohydrates per serving of 10 would have a glycemic load of five.
The glycemic impact diet depends heavily on the calculation of glycemic load. Each food has a different GL, with individual totals being added together throughout the day. A low GL typically falls below a total of 80 per day. Moderate load ranges between 80 and 120. A high glycemic impact diet has a total more than 120.
Diabetics can use a glycemic impact diet to control blood glucose levels. Diets falling into the low GL range have less impact on blood sugar because those foods usually take longer to digest. Higher GL diets are comprised of fast-digesting foods that may spike blood glucose, resulting in a quick drop a short while later. Weight loss may also be a benefit of low glycemic impact diet plans. Foods with high GL digest more quickly and when blood glucose levels rise quickly and fall, hunger can result, as can overeating. Low GL foods take longer to digest and, thus, appetite may be more controlled.
A glycemic impact diet is not the same as low carbohydrate diet. Foods may fall into the category of low glycemic load but contain higher total carbohydrate amounts. Parboiled rice, for instance, has a glycemic load of 22 but contains 40 net carbohydrates per serving. Many low carbohydrate diets allow 20 grams of carbohydrates or less for the first two weeks on the weight loss plan.
Foods in the low glycemic category include skim milk, sweet potatoes, and chickpeas. Lentils, parboiled rice, and apples are also considered to have a low GL. Meats are not typically included on glycemic load lists because they have no carbohydrates.