How Fast Is Your Gut? Understanding Impact Of Gut Transit Time On Health

We often focus on what we eat, but how fast our food moves through the digestive system can be just as important. From the role of bacteria in gut motility to how transit time affects everything from constipation to nutrient absorption, this article explores why your gut’s speed matters and how you can test it at home. Discover simple steps to improve your gut health, whether your transit time is fast or slow

Many of us pay attention to the foods we put in our bodies, asking ourselves whether they're nutritious and healthy. But have you ever stopped to ask yourself how fast this food is moving through your gut?

The answer to this question is important, as the speed at which food moves through your digestive tract affects your health and well-being in many ways. Once you've chewed up and swallowed your meal, this food begins its journey along the gastrointestinal tract – a long and winding pathway that begins at the mouth and ends at the anus. Along the way, it reaches specialist organs that churn and digest (stomach), absorb nutrients (small intestine), and absorb water and salts (large intestine).

The movement of food through the digestive tract is known as gut motility. This process is partly controlled by the trillions of bacteria present in our gut. The gut microbiome is extremely important as these bacteria help develop our immune system and break down food. So, when we eat, we're not just feeding ourselves – we're feeding the micro-helpers present in the intestine. To thank us, the bacteria produce small molecules called metabolites that boost our immune system and keep our gut moving by stimulating the intestinal nerves so they contract and move the food onwards.

Without these bacteria and their metabolites, our guts would be less able to move food through the gastrointestinal tract. This could cause a build-up of ingested material, leading to constipation and discomfort. The time it takes for food to pass from one end of the gastrointestinal tract to the other is called gut transit time. Gut transit time varies from one person to the next. Recent estimates suggest it can take somewhere between 12 and 73 hours for food to pass through the body – with the average being around 23-24 hours. This variation in gut transit explains some of the gut microbiome differences seen between people – and consequently their gut health.

Many factors can also affect our natural gut transit time – including genetics, diet, and our gut microbiome. If gut transit time is long (meaning you have slow gut motility), bacteria in the large intestine produce different metabolites. This is because, just like us, the bacteria in our guts need to be fed. These bacteria enjoy fiber. But, if gut transit time is long and fiber 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. The switch to protein can result in the production of toxic gases leading to health problems such as bloating and inflammation. Slow gut transit can also cause partially digested food to get stuck in the small intestine. 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.

Fast gut transit can negatively impact health, too. There are many reasons that someone may experience fast transit time. For example, anxiety, inflammatory bowel disease (IBD), and irritable bowel syndrome (IBS) can all cause decreased transit time and even diarrhea. In cases of fast transit, the resulting stool is loose with high water content. This indicates that the fecal matter has not spent enough time in the intestine, preventing sufficient absorption of water and nutrients.

In cases of IBD for example, this can lead to dehydration. Testing your gut speed fortunately, there's a very simple at-home test you can do to check your gut motility. It's called "the sweetcorn test". And yes, it is what you're thinking. Don't eat any sweetcorn for 7-10 days (the "wash-out" phase). Then you are ready to begin the test. Note down the date and time, and eat some sweetcorn – corn on the cob or a handful of corn is sufficient. Because the outer shell of the corn is indigestible, it will pass through your gastrointestinal tract with the rest of the food you've eaten and will eventually be visible in your stool. What you'll do is keep an eye on the next few stools you pass and note down the date and time that you observe the golden treasure.

It should be noted that this at-home test is not definitive – but it does represent a measure of transit time that, on average, gives similar results to more sophisticated measures. If you pass the corn in 12 hours or less, your gut is fast. If you don't pass it for around 48 hours or more, then your gut is slow. If you find your gut motility is on either end of the spectrum, there are fortunately things you can do to improve it. If it's consistently fast, it's best to visit your doctor to see if there is an underlying cause. If it's a little slow – but you don't seem to be having any additional gastrointestinal symptoms such as bloating, abdominal pain, lack of appetite, or nausea – eat more fruit and veg to increase the fiber you're feeding those friendly gut bacteria, drink more water and exercise. Following a balanced diet will help to keep your bowels moving and healthy.

(The writer is a senior researcher at The Oxford Centre for Microbiome Studies, University of Oxford)