Bowel Transit Time

Test Overview

A bowel transit time test measures how long it takes for food to travel through the digestive tract. Bowel transit time depends on what types of food you eat and how much you drink. For example, people who eat lots of fruits, vegetables, and whole grains tend to have shorter transit times than people who eat mostly sugars and starches. Because different people have different transit times, experts disagree about how useful this test is.

After you chew and swallow your food, it moves into your stomach, where it is mixed with acid and digestive enzymes. After your food leaves your stomach, it is squeezed through your small intestine, where, vitamins and water are absorbed for use by your body. The food then goes into your large intestine (colon). Whatever hasn't been digested and absorbed by your intestines combines with water, bacteria, and other waste products and becomes stool (feces). Stool is expelled from your body through your anus. The time it takes for food to travel from your mouth to your anus as stool is your bowel transit time.

There are several methods to test your bowel transit time. Each method uses a swallowed substance (called a food marker) that goes through your body and leaves in your stool without being digested. Because the results of these tests are not consistent, experts disagree about their usefulness. Some doctors do not recommend bowel transit time testing.

Dye test

For a dye test, you swallow a pill that has dye in it and keep track of how long it takes before the dye shows up in your stool.

Home test

For a home test, you will drink some red vegetable dye or eat a food like corn kernels or beets. You will then keep track of how long it takes for the dye or vegetable to show up in your stool.

Pellet test

For a pellet test, you swallow small pills (pellets) before having X-rays of your belly. The pellets look like white spots or rings in the X-ray pictures. You will have X-rays over 2 or 3 days to keep track of how fast the pellets move through your intestines.

Why It Is Done

Bowel transit time tests may be done to:

• Help find the cause of severe constipation.
• Show how different foods speed up or slow down the movement of food through the body.

Bowel transit time tests are not done to find the cause of diarrhea.

How To Prepare

If you plan to use food markers (such as corn or beets) to measure bowel transit time at home, do not eat these foods for about a week before starting the test.

If you are using a red vegetable dye, do not eat or drink foods that contain red dye, such as red gelatin or fruit drinks, for about a week before starting the test.

Tell your doctor if you are or might be pregnant before having a pellet test.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

How It Is Done

Dye test or home test

For the dye test or home test, swallow two gelatin capsules filled with a dye called carmine red (Cochineal) or eat a large helping of seeds, beets, or corn kernels to serve as markers. Look at your next couple of bowel movements and write down how many hours it takes after eating until the markers appear in your stool.

Pellet test

Your doctor will give you small, indigestible pellets to swallow with instructions about when to take the pellets. You may have to take them at a certain time for 2 or 3 days in a row. You will then have X-rays taken of your belly. These are usually done on day 4 and again on day 7. Your doctor will compare how many pellets show up on the first X-ray with the number of pellets that can be seen on the later X-ray pictures and also compare where the pellets show up in each picture. This time it takes for the pellets to show up and how fast they move through your intestines is your bowel transit time.

How It Feels

Bowel transit time tests do not cause pain.

You will not feel discomfort from the X-rays used for the pellet test. The X-ray table may feel hard and the room may be cool. You may find that the positions you need to hold are uncomfortable.

Risks

There is no chance for problems from dye tests and the home tests.

The pellet test is not recommended if you are pregnant because the radiation from the X-ray can harm your developing baby (fetus).

Results

A bowel transit time test measures how long it takes for food to travel through the digestive tract.

Bowel transit time depends on what types of food you eat and how much you drink. Different people have different bowel transit times. Talk to your doctor if you do a bowel transit test at home and you do not think that the results are normal.

What Affects the Test

You may have an abnormal bowel transit time if you:

• Have an infection in your intestines.
• Do not drink enough fluids (dehydration).
• Have a disease, such as a narrowing (stricture) in your intestine, an underactive thyroid gland (hypothyroidism), diabetes, or Hirschsprung's disease.
• Are eating less than you usually do or you are eating different kinds of food than usual.
• Take medicines, such as cold medicines, iron, or medicine used to control blood pressure and pain.

Women normally have slower bowel transit times than men.

What To Think About

• The red dye in the gelatin capsules used for home testing is harmless and passes out of your body in your stool.
• Pellet testing is not recommended if you are or might be pregnant.
• Many doctors do not think that bowel transit time testing is useful. Different people have different bowel transit times on different days.
• You can usually speed up bowel transit time if you increase the amount of fruits, vegetables, and whole grains that you eat each day. For more information, see the topic Healthy Eating.
• It is possible to have a daily bowel movement but still have a slow bowel transit time.