Bowel transit time refers to how long it takes for the food to move from the mouth to the anus.
This article discusses the medical test used to determine bowel transit time.
How the test is performed
You will be asked to swallow two gelatin capsules filled with carmine red or another food dye. You take the special capsules with a meal.
Afterwards, you observe your bowel movements and write down how long it takes for the colored dye to first appear. You'll also need to note how long it takes for the color to disappear from the stools.
How to prepare for the test
No preparation is usually needed. However, you should follow any diet or other directions from the health care provider.
How the test will feel
You will not feel the capsules move through your gastrointestinal system.
Why the test is performed
The test helps determine bowel function.
Your doctor may ask you to record transit times as you introduce fiber into your diet. Your diet affects the bowel transit time. For example, if you eat a lot of foods rich in fiber (whole grains, vegetables, and fruits), you will have a more rapid transit time and a heavier, bulkier stool.
The bowel transit time varies even in the same person. The first of the color should appear in the stool about 12 - 14 hours after it is taken. The last of the color will appear within 36 - 48 hours.
What abnormal results mean
If the transit time is 72 hours or more, you may have slowed bowel function.
What the risks are
There are no risks.
The bowel transit time dye test is rarely performed these days.
Andrews JM, Blackshaw LA. Small intestine motor and sensory function and dysfunction. In: Feldman M, Friedman LS, Sleisenger MH, eds. Sleisenger & Fordtran's Gastrointestinal and Liver Disease. 9th ed. Philadelphia, Pa:Saunders Elsevier; 2010:chap 97.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; George F. Longstreth, MD, Department of Gastroenterology, Kaiser Permanente Medical Care Program, San Diego, California. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.