Using the Transit Time Test to Assess Patients’ Bowel Function

 In Gastrointestinal

Dicken Weatherby, ND

When considering mind/body health, one of the first things I think of is the bowels. For peace of mind and sound body, what can be more supportive than good, timely, wholesome elimination? Give that to your patients, and they’ll be happy campers.

On a more serious note, constipation and other bowel complaints often are connected to mental/emotional issues. I use the Bowel Transit Time Test to assess my patients’ bowel function.


Proper elimination of waste is as important as proper digestion. The Bowel Transit Time Test is an excellent way to measure how long it takes for a substance to be eliminated through the bowels. Optimally it should take 18 to 24 hours for food to completely move through the digestive tract. A shorter time is associated with diarrhea, bowel irritation, bowel toxicity, malabsorption and increased peristalsis. A longer transit time is associated with constipation, and increases the likelihood of bowel toxemia and dysbiosis. A longer transit time can also be an indication of low fiber and/or water in the diet, and other digestive problems.


This test uses charcoal, an inert substance, to measure the transit time. Charcoal will stain the stool black or gray, providing a conveniently visible medium for measuring transit time.

The test also provides an opportunity to track any changes in a patient’s stool. The presence of blood, mucus or undigested food particles can provide clues to a patient’s overall gastrointestinal health. I give my patients a handout that asks them to check their stool color, consistency, etc. See the accompanying story, “Directions for Bowel Transit Time Test,” for details.

Clinical Implications

Following are some of the clinical implications associated with brief, delayed and prolonged bowel transit times.

Normal Transit Time with Residual Color on Next Stool: This indicates that patients have an optimal transit time but may be lacking in fiber or water, as the charcoal should be expelled in one bowel movement.

Fast Transit Time (ie, less than 18 hours): A fast transit time is associated with diarrhea, which may be acute or chronic. A fast transit time can be due to a gastrointestinal infection from the following:

  • Parasitic infection (Giardia lamblia, Entamoeba histolytica, Cryptosporidium, Isospora)
  • Viral infection (Enterovirus, rotavirus)
  • Bacterial infection (Campylobacter jejuni, Shigella, Salmonella, Yersinia enterocolitica)
  • Intestinal toxins (Clostridium, coli, Staphylococcus).

A fast transit time is often associated with a previous antibiotic therapy that has altered the gastrointestinal terrain to such an extent that both digestion and elimination are compromised. A fast transit time may also be due to the use of laxatives or other medications that cause an increased peristalsis within the gastrointestinal tract. One of the main concerns with a chronic fast bowel transit time is malabsorption of key nutrients, both fat- and water-soluble, and dehydration. Digested food matter needs to spend enough time in the small intestine for optimal absorption of nutrients. A rapid transit time does not allow for this absorption to take place.

Other conditions to consider include inflammatory bowel disease; irritable bowel; malabsorption; leaky gut syndrome; emotional stress; food allergies; carbohydrate malabsorption (lactose intolerance); wheat allergy; excess consumption of non-metabolized carbohydrate sweeteners (maltitol, sorbitol, etc.); excess vitamin C intake; insufficient bile output due to gallbladder insufficiency causing fat malabsorption and steatorrhea; and laxative abuse.

Slow Transit Time (ie, more than 24 hours): There are organic, functional and even mental/emotional reasons a patient may present with a slow bowel transit time.

  • Organic causes include diverticulitis, fissures, weakness in the rectum or sigmoid colon (often caused by laxative abuse), impaction of fecal material in the bowel, a mass of some kind obstructing the bowel (tumor or pregnancy), or inflammation or spasm from pain in the rectum or anal canal.
  • Functional causes include a diet that is irritating to the colon, lack of bulk to the stool, lack of fluids, insufficient digestion (hypochlorhydria and/or pancreatic insufficiency), stress, hypothyroidism, poor bowel tone, infection or even adrenal dysfunction.
  • For some, a slow bowel transit time may have a mental/emotional etiology. A patient may have a neurogenic constipation caused by a repeated voluntary resistance of the urge to have a bowel movement. Periods of increased stress can exacerbate the constipation, increasing sympathetic outflow, which causes the blood vessels of the colon to constrict (cold, pain, fear, etc.)

Directions for Bowel Transit Time Test

Supplies: Eight charcoal capsules or tablets (which is enough for two tests)

Directions for patients:

  • Swallow four charcoal capsules at the evening meal.
  • Record the date and time capsules were swallowed.
  • After every bowel movement, observe the stool under bright light.
  • Upon first sight of a black or charcoal-gray stool, record the date and time and mark this as “time that color first appears.”
  • Calculate the number of hours between when capsules were swallowed and when “color first appears,” and note this time (in hours). This is the time it took for the charcoal to pass through the digestive tract.
  • Continue to examine every stool, and note the time and date when the black/charcoal-gray color has completely disappeared.
  • (Ideally) Wait five days to allow the marker to clear fully from the intestines, and then repeat the process.

Further assessment tools are available. Use the above guidelines as a start, and you’ll be on your way to helping patients with this crucial mental-emotional-physical support of proper elimination.

WeatherbyDicken Weatherby, ND is based in southern Oregon. A graduate of NCNM, Dicken is co-author of the best-selling book Blood Chemistry and CBC Analysis – Clinical Laboratory Testing from a Functional Perspective. He has self-published seven other books in the field of alternative medical diagnosis, including The Complete Practitioners Guide to Take Home Testing, which includes a chapter on bowel transit time. He also has created numerous information products, and runs a number of successful Web sites (, and He is involved in research, writing and consulting, and teaches functional diagnosis seminars in both the US and his native country, the UK.


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