GI and GL are useful ways of ascertaining the way food will break down in our body once eaten, and seeing which foods take longer and so are healthier and more available as fuel. As a basic principle processed foods are high GI and high GL, and whole-foods and vegetables are low GI and GL. GI is a useful guide, but GL (glycemic load) is more accurate. They are more valuable ways of measuring foods than calories as they guide us towards healthier foods and help explain our bodies relationship to food. It’s about balance. Many fruits for example may be high GI and GL, but they are wonderfully healthy and delicious foods, don’t avoid them unless you have specific health reasons for doing so such as being type 2 diabetic or arthritic, when you may want to limit some fruits.
Glycemic Index (GI) is a figure representing the relative ability of a carbohydrate food to increase the level of glucose in the blood. So, how quickly a food breaks down in the body, and is available as glucose.
The number usually ranges from 50 to 100, 100 being pure glucose.
Glycemic Load (GL) is a ranking system for carbohydrate-rich food that measures the amount of carbohydrates in a serving of food. It is a more realistic, less abstract measurement than GI, as it takes the effect of carbohydrate on blood sugar into account. An example of this is the parsnip, it has a high GI, but in reality a low GL, and so is a healthy food to regularly eat and enjoy.
Foods with GL of below 10 are considered to be low GL, and above 20 is high.