Gut anatomy and function

Gut transit time

Also called: bowel transit time, intestinal transit time

Gut transit time is the total time from eating food to passing it as stool. The healthy range is 12 to 48 hours, with most adults sitting around 24 to 36 hours. Less than 12 hours suggests fast transit (often diarrhoea-predominant), more than 72 hours suggests slow transit (constipation-predominant). You can measure it at home with the corn test, eat a portion of sweetcorn and time when you see kernels in your stool.

What's normal

  • Stomach: 2-5 hours to empty.
  • Small intestine: 2-6 hours to traverse.
  • Colon: this is where most of the variation lives. 10-59 hours.
  • Total mouth-to-toilet: 12-48 hours typical, 24-36 hours average.
  • Women generally have slightly longer transit times than men, by roughly 1 to 4 hours on average.
  • Transit time slows with age, with low fibre intake, and with sedentary lifestyle.

How to measure it

The simplest at-home test is the corn test. Eat a portion of sweetcorn (about 100 g, well-chewed). Note the time. Watch your stool. Note when you first see corn kernels appearing, this is your transit time. Whole corn kernels pass through largely undigested because of their tough cellulose coat. Other markers that work: beetroot (red colour in stool), sesame seeds, blueberry skins. Repeat 2-3 times for an average. For more accurate clinical measurement, smart pills (SmartPill, 3D-Transit) record transit and are used in gastroenterology clinics.

Slow transit (over 48 hours)

  • Hard, dry, difficult-to-pass stools.
  • Fewer than 3 bowel movements a week.
  • Bloating that builds through the day.
  • Often paired with low fibre, low water, low movement.
  • Common causes: low-fibre diet, dehydration, sedentary lifestyle, opioid medications, GLP-1 drugs, hypothyroidism, magnesium deficiency, diabetes, Parkinson's.
  • What helps: 25-30 g fibre a day, 2 litres water, daily movement, magnesium citrate at bedtime if needed.

Fast transit (under 12 hours)

  • Loose, watery, urgent stools.
  • Multiple bowel movements a day.
  • Visible undigested food.
  • Often paired with IBS-D, post-infectious IBS, bile acid diarrhoea, lactose intolerance, anxiety.
  • What helps: low-FODMAP trial, soluble fibre (psyllium, oats), smaller more frequent meals, ruling out bile acid diarrhoea.

Why it matters

Transit time shapes your gut microbiome. Slow transit means food sits longer, fermentation goes further, and you get more gas and more bloating. Fast transit means less time for the colon to extract nutrients and water.

Common questions

Why is mine longer than my partner's on the same food?
Sex (women's transit times average roughly 1-4 hours longer), microbiome composition, hormonal cycle phase, exercise level, fluid intake, and individual gut motility all vary. Your transit time is your transit time. Comparing to a partner is less useful than tracking your own changes.
Does fast transit mean I'm absorbing fewer nutrients?
Slightly, but the body is forgiving. Most absorption happens in the small intestine over 2-6 hours, and that step is preserved even when colonic transit is fast. The exception is severe diarrhoea or short bowel syndrome where deficiencies can develop.
Can I speed up my transit time?
Yes. Most reliable: 30 minutes of daily walking, 25-30 g of fibre, 2 litres of water, and not skipping breakfast. Coffee in the morning works for many people through the gastrocolic reflex. Magnesium citrate or psyllium husk add a more direct effect when needed.
Is the corn test accurate?
Reasonably. It gives a rough estimate that on average lines up with more formal transit measures, though it has not been validated to a specific margin against smart-pill testing. Useful for trend-tracking, not for diagnosis. Repeat 3 times for a stable average.

Sources

The Book of Suna is general information, not medical advice. It is not a substitute for talking to a qualified healthcare professional about your own situation.