If we need to lower blood glucose, we need to decrease the intake of high glycemic index foods. The Glycemic Index (GI) shows what happens to your blood sugar when you consume particular foods, e.g., if you consume 50 gms of a particular food, than this food raises your blood glucose to a certain level.
Carbohydrates hat breakdown quickly during digestion have the highest glycemic (presence of glucose in the blood) indexes.
The two hour blood sugar response of a high GI food v/s a low GI food.
Glycemic Load (GL)
Glycemic Load (GL) is a more realistic tool to assess the "glycemic response" to food, i.e., the response of the body to the presence of glucose in the blood by eating that food.
It takes into account the carbohydrate content of the food and the portion size.
Therefore, GL = Carbohydrate content /Quantity (Carb. eaten) * GI.
Thus, GL of watermelon - 100 gms of watermelon with a GI of 72 and a carbohydrate content of 5 gms (as mostly water only) is calculated as 5/100*72=3.6, so the GI is 3.6. Other good example is pop-corn which is high in GI but low in GL. However, apply your judgment (discretion) when comparing GI v/s GL.