First published September 2021
Updated September 2026
What can your poop tell you about the tiny, helpful bacteria living inside your gut? Quite a bit!
Your intestines are home to trillions of bacteria that help digest food, absorb nutrients, and keep your body running smoothly. Scientists around the world are studying these microbes to learn what combination of bacteria creates the healthiest gut. Because these bacteria live deep inside your digestive tract, studying your stool (poop) is the easiest way to see how they are doing.
Researchers in London found a simple way to measure gut transit time, or the amount of time it takes for food to travel from your mouth, through your stomach and intestines, and out as stool.
Why Color Matters
Under normal conditions, your stool gets its typical brown color from a compound called stercobilin. This is created when your healthy gut bacteria break down bilirubin, a natural compound produced by your liver to help digest fats. Because your stool is usually brown, any sudden change in color stands out clearly.
While hospitals have advanced tests to measure how fast food moves through your body, those tests can be expensive, time-consuming, and uncomfortable. The London researchers realized you can track your gut speed right at home using colorful foods.
The At-Home Blue/Red Food Test
You can measure your own gut transit time using a simple, safe home test:
Prep your diet: Avoid eating beets, corn, or foods with bright dye for 1 to 2 days before starting.
Eat the test food: Eat a noticeable food—like a half to a whole red beet, or a serving of sweet corn—and write down the exact date and time you ate it.
Track your stool: Pay attention when you go to the bathroom over the next few days. Write down the exact time you first see the red color or corn kernels in your stool.
Calculate your time: The hours between eating the food and seeing it in your stool is your gut transit time.
What Do Your Results Mean?
In the study, the average transit time was about 28 hours, though anywhere between 12 and 60 hours is considered normal.
Keep in mind that your transit time can change from day to day. Many everyday factors influence how fast food moves through you, including:
How much water you drink
Fiber and caffeine in your diet
Physical activity and exercise
Certain medications
Stress and overall health
This easy DIY test gives you a fascinating peek into your digestive system and how your gut bacteria work to keep you healthy.
When to See a Doctor
While a home test like the "beet test" is a great way to learn about your body, tracking your transit time can also highlight when it is time to check in with a healthcare provider.
Schedule an appointment if:
Your transit time is consistently outside 12 to 60 hours: Consistently very fast (under 12 hours) or very slow (over 60 hours) transit times can affect how well your body absorbs nutrients and can disrupt your gut bacteria.
You notice a sudden, lasting change: If your bowel habits or transit times change significantly for more than two weeks without an obvious reason (like a change in diet or travel), let your doctor know.
Red Flag Symptoms
If you experience any of the following symptoms along with changes in your bowel habits, do not rely on home testing—contact a doctor promptly:
Unexplained weight loss: Dropping weight without trying or changing your diet.
Blood in your stool: Stool that appears bright red, dark maroon, or black and tarry.
Changes in stool shape: Stool that becomes consistently thin or pencil-like.
Severe abdominal pain: Intense belly pain, cramps, or pain that wakes you up at night.
Persistent fever or vomiting: Especially when accompanied by severe constipation or diarrhea.
Tracking your symptoms and sharing specific transit times with your care team gives them valuable clues to help customize your treatment plan.
Rajitha D. Venkatesh, MD, MPH, FAAP, is an attending pediatric gastroenterologist at Nationwide Children’s Hospital and Co-Director of the Eosinophilic GI Disorders Program. She is also an assistant professor of Clinical Pediatrics at The Ohio State University College of Medicine. Dr. Venkatesh attended Wilkes University for her undergraduate education as a Wilkes Scholar. She attended SUNY Upstate Medical University for medical school and was selected as a NIH Fogarty Clinical Scholar. She completed residency training in Pediatrics at Yale-New Haven Children Hospital, and fellowship training in Gastroenterology, Hepatology & Nutrition at Massachusetts General Hospital for Children (MGHfC).
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