As a health editor, I’ve gone to some fairly extreme lengths to assess and improve my gut health. I’ve bottled up stool samples and sent them, in the post, to labs in foreign countries. I’ve had my CRP levels assessed (that’s a protein in the blood that increases during inflammation). I’ve ordered probiotics, prebiotics and postbiotics. Lots of them are still languishing, ¾-full, in the back of the drawer specifically designated for kitchen clutter.
You can spend a fortune on your gut health, if you should wish. And if you’re unlucky, you can emerge absolutely none the wiser. Gut health isn’t only highly individualised, but it also impacts (and is impacted by) a host of factors, from your stress levels to genes via your environment. It can feel like a maze, and one that’s very expensive to navigate.
There is, however, one important factor that’s easy and entirely free to explore: the speed at which your food moves through you.
Why it matters?
Once you chew and swallow your breakfast, its journey through your digestive tract is sped along by contractions and relaxations of the muscles in your GI tract in a process known as ‘gut motility’. That process is also influenced by the trillions of bacteria living in your gut (your gut microbiome).
Like most things gut-health, this relationship is complicated. Because while these bacteria produce metabolites (typically, small molecules) that stimulate motility, their health and diversity is also impacted by your motility. It’s a two-way street, but in essence, “your gut transit time, or how long it takes between you first eating something and it coming out the other end, is a fun way of checking how healthy your gut is,” says Dr Emily Leeming, microbiome research fellow and author of Genius Gut.
So how do you test it?
First, a warning. It’s probably best not to read further if you’re currently eating your breakfast.
In 2021, Dr Leeming co-authored a research paper (called the Blue Poo paper), in which participants were given two very heavily died blue muffins and reported back on how long it took for them to produce a blue poo. You don’t have to go this far.
The first step is not to eat any sweetcorn for a week (this is known as “the wash-out” phase). Next, open a tin and eat a handful of kernels and make a note of the date and time. Then… wait. Because the hull (or outer layer) of a corn kernel is made up mostly of cellulose that doesn’t break apart easily when chewed, you should be able to see it quite clearly in your stool. So wait and watch. And then note down the time and date of its eventual sighting.
What’s normal?
When the personal nutrition company ZOE measured gut transit times, the results varied widely. Some reported times of less than 12 hours, others were many days. The typical time was around 29 hours.
The researchers found marked gut microbiome differences between those with short transit times and those with longer transit times.
So what does it mean if yours is short?
According to ZOE: “Shorter transit times were generally linked with better health, healthier responses to food and less visceral fat, which sits deep within the belly.”
That said, a very fast transit time was not such a good sign, correlating with a less-healthy microbiome and possibly indicating diarrhoea, too. In fact, if faecal matter moves too fast through your system, your intestine won’t have had enough time to absorb water and nutrients.
So, how short is unusually short? Under 14 hours, says Dr Leeming.
And if it’s long?
“If gut transit time is long (meaning you have slow gut motility), bacteria in the large intestine produce different metabolites,” explains Nick Illot, senior researcher at the Oxford Centre for Microbiome Studies. “This is because, just like us, the bacteria in our guts need to be fed. These bacteria enjoy fibre. But, if gut transit time is long and fibre is taking too long to reach the large intestine, these microbial inhabitants have to switch to an alternative food source. So, they turn to protein.”
That switch can lead to toxic gasses being produced in your gut, which in turn can create bloating and inflammation.
There’s more. “Slow gut transit can also cause partially digested food to get stuck in the small intestine,” says Nick. “This has additional health consequences – such as an overgrowth of small intestinal bacteria, which can lead to symptoms such as abdominal pain, nausea and bloating.”
In Dr Leeming’s study, transit times of more than 58 hours tended to point towards bacteria that are linked to poor cardio-metabolic health (bad heart and metabolic health).
So what can you do?
If your results are consistently fast, you should book an appointment with your GP to investigate the reasons for that, suggests Nick. Ditto if they’re consistently slow and you have other troubling symptoms, such as low appetite and abdominal pain.
If you don’t have those symptoms, Dr Leeming suggests one simple fix: fibre. “It’ll slow things down if your transit time is too fast, and speed it up if it’s too slow,” she explains. “That’s because fibre does many things in your gut – it helps you absorb water and keep your poo soft, but it also provides extra bulk and roughage to slow transit down to optimum time. Plus, it feeds your gut microbiome.” 90% of us are not getting enough, and it’s easy to boost your intake by eating more beans, wholegrains, nuts and seeds. No expensive tests or supplements necessary.
