Sci Snippet – How long from eating to pooping?

Based on my two posts about poop (Facts about Poop and Fecal Transplant), I received a great question about how long it actually takes for food to pass through the gut? Although I posted my answer in the comments and on Facebook, here is the answer with a few more details in case you didn’t see it.


Thanks to North Shore Colonics for the image

The actual time from mouth to pooping depends on a number of factors (for example, what you eat and drink), and can be a critical measure of how the bowel is functioning – because we all know that things just aren’t right if we’re constipated or have diarrhea. There are a number of ways to measure “colon transit time” or “whole gut transit time”, but the most common is having subjects swallow 20-25 radioactive markers in a pill (link to what they look like here). The poop is collected and the number of radioactive rings in the stool are counted. And just in case you’re imagining researchers poking through poop – they didn’t have to do that! Because the rings are radioactive, they can count them using an x-Ray. After 5 days, researchers found that on average 80% of these rings were expelled, and 20% were still making their way out (the journal article is here). In one study, the median whole gut transit time is 27.7 hours though in other studies they find the mean to be slightly longer at 30-40 hours. Also, in general women had longer transit times than men – maybe because women’s intestines are, on average, about 10 cm longer than men’s. As an aside, you may wonder to yourself “why are women’s intestines about 10 cm longer than men’s?”  It’s not entirely known but two prevailing theories are 1) to get around the larger female internal organs like the ovaries or 2) to absorb more nutrients during pregnancy. This transit time is also affected by race – transit time is much shorter in Chinese men and women.

As you can imagine, this is a bit of an imprecise way to measure transit times and researchers are creating new tools (like electronic wireless motility capsulesthat can more accurately track how things transit through the gut. Or you can be like my friend Sarahjane who says that she informally tracks this using one of the lowest-tech options of them all – corn!

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