Glucose, is an important energy source that is needed by all the cells and organs of our bodies. Blood glucose testing is one part of managing your diabetes successfully. Testing your blood glucose both before and after a meal allows you to see how that meal affects your blood glucose levels and helps you to understand which meals may be best for your blood glucose control. The most powerful influence on blood glucose levels comes from food. Whether you have type 1 or type 2 diabetes. The peak blood glucose levels are often likely to occur around two hours after meals.