February 24, 2025, 2:28 pm | Read time: 5 minutes

Many people pay attention to what they eat — but few think about how long it takes for food to leave the body. However, the speed at which our digestion works can have a decisive influence on our health. But how do you measure intestinal transit time? A scientist at Oxford University has a simple trick. FITBOOK nutrition expert Sophie Brünke also explains what exactly happens in the body during digestion and which factors can slow down or speed up the process.

How Digestion Works and How Long It Should Take

Strictly speaking, digestion begins in the mouth. This is where we chew our food, and the first enzymes from our saliva begin to break down the food components. Then things really get going in the stomach: the chyme is broken down, mixed with digestive juices, and gradually passed on to the small intestine. The stomach acts as a kind of temporary storage area where food can remain for up to four hours. Secretions from the pancreas and bile are added in the small intestine. This is mainly where nutrients are absorbed, which can take seven to nine hours. In the large intestine, the food thickens. In other words, water is removed from the food residues before the indigestible remains are excreted. This process can take longer than a day.

Of course, the intestinal transit time is individual and depends on various factors. While some people have completely digested their food within twelve hours, for others, it can take up to 73 hours. On average, the process takes around 23 to 24 hours.

Too Fast or Too Slow? What Happens in the Body

One of these influencing factors is the intestinal flora – often referred to as the intestinal microbiome. It describes the entirety of the bacteria living in our intestines. This is because the movement of food through the digestive tract, known as intestinal motility, is influenced by these trillions of bacteria, among other things. These microorganisms not only help with digestion; they also produce metabolic products that strengthen our immune system and regulate intestinal motility. A small example: when we eat fiber, the bacteria ferment it into short-chain fatty acids, which in turn have an anti-inflammatory effect.

A problem arises when the intestinal microbiome consists of an unfavorable constellation of bacteria — this can be the case, for example, as a result of an unhealthy diet or the intake of antibiotics. This can affect the intestinal transit time.

Slow Intestinal Transit Time

A longer passage time means that the bacteria in the large intestine have to switch to alternative sources of nutrients to their beloved dietary fibers, as these take too long to reach them. The choice often falls on proteins, which favors the production of unwanted metabolic products. This can cause bloating and inflammation.

As a result of slow intestinal transit, food that has already been digested can also get “stuck” in the small intestine. This has other unpleasant health consequences, such as an overgrowth of bacteria in the small intestine, which can lead to symptoms such as abdominal pain, nausea, and bloating.

Rapid Intestinal Transit

There are many reasons that can lead to accelerated digestion. Anxiety, inflammatory bowel disease (IBD), and irritable bowel syndrome (IBS) can shorten the time and even cause diarrhea, reduced nutrient absorption, and dehydration. This is because, in this case, the stool tends to be too soft and has a high water content. It has not been dehydrated long enough in the large intestine.

Simple Test for Intestinal Transit Time

If you’re eager to determine your own intestinal transit time, you can use Nick Ilott’s “sweetcorn test” at home. Perhaps the buzzword already gives you an idea — and yes, that’s exactly what he means. As the outer husk of corn is excreted undigested, it is a handy visual marker for intestinal transit time.

How the corn test works:

• Avoid corn for seven to ten days to make sure there are no leftovers in your digestive tract.
• Then, eat a handful of corn kernels or a corn cob and note the date and time.
• Observe your subsequent bowel movements and note when the first kernels of corn reappear.

Evaluation:

• If the corn appears within twelve hours, the intestinal passage is fast.
• If it takes longer than 48 hours, it is slow.

Ilott points out that this test does not replace a medical diagnosis but can provide helpful information on digestive health.

More on the topic

Good to know Why fiber is so important for the body

For a Feeling of Fullness 11 Tips on How to Stimulate Digestion

According to a Study Dairy Products Are Good for the Gut — Apparently with One Exception

How to Do Something Good for Your Gut

If intestinal transit is consistently too slow or too fast, it is advisable to seek medical advice to rule out possible underlying illnesses. In the case of slight deviations without additional symptoms, simple lifestyle and dietary adjustments can often lead to an improvement.

It’s important to ensure adequate fluid intake and a sufficient amount of fiber — aiming for at least 30 grams per day. Fiber is mainly found in plant-based foods such as fruit, vegetables, wholegrain products, pulses, nuts, and seeds. Fermented foods such as sauerkraut, kimchi, or kombucha also promote bacterial diversity.

Sufficient exercise in everyday life also stimulates intestinal activity. Specific yoga exercises, like the cat-cow and sun salutation, can be particularly beneficial.