The easy way to check your gut health (for free)

Telegraph

05-03-2025

There's no doubt that gut health is important. Having a diverse range of bugs, or microbes, living in our small and large bowel has been linked to a lower risk of heart disease, Type 2 diabetes and even arthritis.
This explains why the gut health market is booming – valued at more than £40 billion globally – and there's been an explosion of gut friendly foods and supplements which now sprawl across supermarket shelves, as well as costly tests promising to report back on the health of your gut.
But there's a simple way you can check in on your gut health at home, for free – providing you have a tin of sweetcorn in your cupboard – and that's by testing your gut transit time.
'Gut transit time is the time it takes for food to move through your digestive system, from when you eat it to when it exits as poo,' explains Dr Emily Leeming, a microbiome scientist, dietitian and author of Genius Gut. 'It's a useful simple way to understand how well your gut is working.' A faster or slower transit time can influence which microbes thrive in your gut and and affect what molecules they make and whether these help or hinder your health.
In a study that Dr Leeming co-authored, a healthy gut transit time was linked to having diverse gut microbes and it was a more accurate indicator of general health than stool consistency or frequency. Here's how to test yours.
How to do the sweetcorn test
Firstly, avoid eating any sweetcorn for a week or two, to make sure your gut is clear of the vegetable. Then, eat a portion of it – around three heaped tablespoons, one whole cob or two half cobs.
'Note the time you ate it, making sure not to chew the kernels too much so you can spot them later,' Dr Leeming recommends. 'Then, keep an eye on your poo over the next few days and note when you first see the corn again.'
The time between eating the sweetcorn and seeing it in your stool is your gut transit time.
There isn't a single sweet spot that is considered healthy gut transit time but the average is around 24 hours and falling within 14 to 58 hours is considered healthy, Dr Leeming says.
'It is important to note that it is not a perfect measurement,' notes Nick Ilott, a senior researcher and lead bioinformatician for The Oxford Centre for Microbiome Studies. 'So if it takes two days then your gut transit time is unlikely to be exactly two days – but it is an indication.'
If you don't like sweetcorn, another way of doing this test is to bake something, such as muffins, and include blue dye in the mixture. Later, you should be able to spot it in your stool.
What your result means
Four hours
If the time between eating sweetcorn and seeing it in your stool is just four hours, this is a very fast and short transit time and likely means you have diarrhoea, Dr Leeming explains.
'This could mean your body isn't absorbing nutrients properly, and that you have an imbalanced gut microbiome,' she says.
You may also be suffering from some unpleasant gut symptoms, such as bloating and discomfort, caused by your microbes producing gases because of a lack of nutrients, Ilott says.
'If transit time is fast (four to 12 hours) then you may risk becoming dehydrated,' he notes.
Your gut transit time can fluctuate based on what you've eaten, Dr Leeming adds. Also, a fast gut transit time can be caused by anxiety, inflammatory bowel disease or irritable bowel syndrome.
'You should always check with your doctor if you are experiencing any gut symptoms that you feel are abnormal,' Ilott says.
24 hours
'This is within the healthy range,' Dr Leeming explains. Her study linked healthy gut transit times with better overall health, healthier responses to food and less visceral fat (the type that sits deep within the belly and increases the risk of heart disease and stroke).
'You likely are eating a healthy amount of fibre, and your gut microbiome tends to be healthier than those with a very short fast transit time, or a longer transit time of above 58 hours,' she adds.
58 hours
If it is 58 hours or more before sweetcorn appears in your stool, it means that you have a long, slow gut transit time, Dr Leeming says.
'This means that you are more likely to have a less healthy gut microbiome,' she notes. 'That could be because the gut bacteria aren't getting enough of their favourite food, ie fibre, delivered to them often enough, and may mean that they then produce less healthy molecules.'
If fibre isn't reaching the gut often or quickly enough, microbes start feasting on protein instead, which can lead to bloating and inflammation.
Dr Leeming and colleagues also found that longer transit times were linked to having a less healthy gut microbiome and having more visceral fat build up around the organs.
How to improve your gut transit time
Whether your gut transit time is on the short or long side, eating more fibre is likely the answer, Dr Leeming says. 'Fibre acts to slow down fast transit times, and also speed up those that are too slow,' she explains.
'Only 7 per cent of people in the UK are eating the recommended amount of 30g of fibre a day,' Dr Leeming says. In fact, the average intake is just 18g.
Beans, whole grains, nuts and seeds are some of the most dense sources of fibre and there's also plenty of it in vegetables and fruit.
To increase your intake, 'swap your bread for a pumpernickel rye bread, that contains 7g of fibre a slice, and snack on a handful of nuts and seeds a day,' Dr Leeming suggests.