Fasting is also a component of the preparation for a colonoscopy. The duration of the fast will depend on several factors, such as the time of the actual test. In many cases, colonoscopies are done in the morning in order to avoid having patients fasting all day long before their test.
Every physician will have their own colonoscopy prep instructions, which should be followed closely. The day before the test is generally devoted to prepping, and in most cases, patients are advised to follow a clear liquid diet starting in the late afternoon. Clear liquids include water, tea, coffee, ginger ale, 7-Up or Sprite, apple juice, and white grape juice. Sugar, honey, or artificial sweeteners are generally allowed in tea or coffee, but check with your doctor to be sure.
What is not allowed prior to a colonoscopy is milk, soy milk, creamer, or any other dairy product. These should not be taken in coffee or tea before a colonoscopy. Depending on the time of the test, even clear liquids must be discontinued a few hours prior to the colonoscopy. For a morning test, a morning cup of coffee may not be allowed (check the prep instructions or call the doctor's office if the instructions are unclear). For an afternoon test, a morning cup of coffee might be permitted (again, without any dairy products), but could be limited to just one cup, and only several hours before the test.
If there is any doubt about the prep instructions, check with the physician's office. Accidentally eating or drinking something too close to test time could affect the results, and possibly require a second test to be done (and therefore, a second prep).
Espat A. "Ensure Success with Colonoscopy Prep." MD Anderson Cancer Center. Mar 2010. 6 May 2013.
Setter T. "Todd’s Six-Day Colonoscopy Prep Guide." Colon Cancer Alliance. 2013. 6 May 2013.