Prior to having blood work done, it is best not to eat any food at all and not to drink anything that is not water. Most doctors recommend that patients stop eating and drinking 8 to 12 hours before the time of their blood draw.
Doctors also recommend bringing snacks to the doctor's office so that after the test, patients can eat immediately to help with any dizzy or lightheaded feelings that some people experience. Water is always allowed before and after a blood draw. Furthermore, water is recommended because it helps keep the veins thick so that the needle can easily find the vein as well as the phlebotomist.