Positron emission tomography, or a PET scan, is a type of nuclear medicine imaging that views the body and organs on a cellular level, according to RadiologyInfo.org. A PET scan measures body functions like blood flow, oxygen use and the metabolism of glucose, or sugar. Depending on the type of PET scan you have, following a low-carbohydrate diet 12 hours before the scan may be necessary to increase the quality of PET scan images. Foods you can eat are limited for this type of PET scan. Begin your low-carbohydrate diet 12 hours before your scheduled PET scan unless otherwise instructed by your physician, suggests Cedars-Sinai Medical Center. All meats are allowed prior to a PET scan, including beef, chicken, pork and fish.