Why do I need to fast before my test?

Food is broken down into simpler forms (glucose) by the digestive tract and is released into the bloodstream, which then circulates and helps provide energy to the body cells. Therefore, the amount of glucose present in the blood sample after having a large meal will be higher than any other time of the day. Likewise, blood cholesterol and triglyceride levels measured before a meal are lower than the reading taken after a meal. In brief, consuming food before blood collection gives inaccurate results, because the test outcomes are influenced by the type of food and the size of the serving.