Carbohydrate macronutrients comprise sugar, starches and fiber. These are found in a large variety of foods, from grains and legumes to fruits, dairy products and sweets, but not all carbs influence your health the same way. Some carbohydrates are considered healthier than others; the glycemic index and the glycemic load are two of the best tools to evaluate the impact of these foods in your body.
Available Carbohydrate
When you look at a food label, the total amount of carbohydrates listed is the sum of the grams of sugars, starches and dietary fibers. However, only sugars and starches are fully digested, absorbed and metabolized in your body. Dietary fiber remains undigested in your gastrointestinal tract, where it plays a key role in regulating your bowel movements. Because fiber does not influence your blood sugar levels and does not provide any calories, you subtract it from the mass of total carbohydrates in a food to obtain what is called available carbohydrates. Available carbs are sugar and starch only, and this figure is used to calculate the GI and GL.
Glycemic Index
The GI of a food is calculated by feeding healthy volunteers a serving containing the equivalent of 50 g of available carbohydrates. Then, their glycemic response, or their blood sugar concentration, is measured for a period of at least 2 hours and compared to the response obtained after eating 50 g of pure glucose. For example, if the rise in blood sugar over 2 hours that is observed after eating a banana represents 52 percent of the rise observed after consuming pure glucose, the banana gets a GI value of 52. GI values usually range between 0 and 100. A GI of 55 and under is low, between 56 and 69 is medium, and 70 and higher is high.
Glycemic Load
The GL is calculated by multiplying the GI of a food by its available carbohydrate content, divided by 100. For example, a medium banana, with an available carbohydrate content of 25 g and a GI of 52, has a GL of 13. GL values of 10 and below are considered low, those between 11 and 19 are medium and values 20 and above are considered high.
Glycemic Index Vs. Glycemic Load
The main difference between the GI and GL of a food is that the GI reflects only the quality of the carbohydrate contained in a food, while the GL reflects both the quality and the amount of carbohydrate in a serving of food. Lowering your dietary GI is associated with a healthier body weight, more stable blood sugar levels and higher heart-protective HDL cholesterol levels. A lower dietary GL is associated with a reduced risk of heart disease and type 2 diabetes. Therefore, both concepts are useful for improving your health, although the glycemic load may be more complete by taking into consideration both the amount and type of carbohydrates consumed in your diet.
