A mammogram does not require fasting. Mammograms are different from GI exams because food can affect contrast imaging, so you must fast for at least 6 hours before the exam, with no food or water. Mammograms do not involve the digestive tract and therefore do not require fasting. If the mammogram is performed on an empty stomach, conditions such as emotional stress when the patient is standing or under pressure can adversely affect the mammogram, so it is not recommended that the patient perform the mammogram on an empty stomach.