Table of Contents
Did you know that the speed at which your body digests food not only affects your feeling of fullness, but can also provide clues about your overall health?
This may surprise you, but in fact, research (including mine) shows that intestinal transit time (the time it takes from when a food is ingested to when it is digested and excreted as waste) may be related to digestive problems. health.
Think of gut transit time like a train ride: If the train moves slowly or stays at a station too long, everything moves backwards, causing delays and inconvenience. But if the train passes through stations too quickly, it misses important stops where passengers must get off.
For example, a slow intestinal transit time is associated with an increased risk of colon cancer, according to a study published in the British Journal of Cancer in 2004, possibly because it prolongs the exposure of the intestinal wall to possible carcinogens in feces.
A slow transit time could also affect the gut microbiome, the community of bacteria and other microbes that live there and play a key role in our health.
In my own research, published in the journal Gut in 2021, my colleagues and I found that a slow transit time of more than 59 hours was associated with higher levels of “bad” gut bacteria that had previously been linked to markers of bad heart health. and inflammation.
Similarly, a recent study in the journal Cell showed that people with a slow transit time tend to have a higher microbial load (the total number of bacteria in the gut).
While this is not inherently harmful, it can have negative consequences under certain conditions. Normally, gut microbes are excreted in feces. But when transit time is slow, they are not eliminated and continue to multiply.
Registered dietitian Dr. Emily Leeming explains that intestinal transit time (the time it takes from ingesting a food to digesting it and excreting it as waste) can be linked to health problems.
This creates more microbes to feed, while their food source, primarily fiber, becomes scarcer as it takes longer to reach them. Microbes can end up producing harmful byproducts related to inflammation, which is often a precursor to disease and illness.
(This is one of the reasons I advise people to eat more fiber; 90 per cent of the UK population does not reach the recommended 30g of fiber a day – just remember to drink enough fluids too).
But a rapid intestinal transit time can also cause problems. Food that moves too quickly through the intestine can lead to poorer nutrient absorption, leading to energy crashes and leaving you feeling hungry shortly after eating.
It can also reduce the total number of microbes living in your gut (some of which play a vital role in protecting against infection or are linked to mood); This is because rapid transit limits the time bacteria have to interact with the food you eat. and produce the molecules that support your well-being.
While occasional bouts of rapid transit, such as when you’re nervous (when your body’s fight-or-flight response kicks in, speeding up digestion), won’t cause harm, frequent occurrences can make you feel fatigued, moody, or evil. .
The optimal point for digestion is believed to be between 14 and 58 hours. This is enough for nutrients to be absorbed, but not so much that gut microbes begin to run out of their preferred food source.
This balance supports a “healthy” gut microbiome, allowing for the production of healthy molecules, such as short-chain fatty acids, that support your immune system and gut health.
So how do you measure intestinal transit time?

Certain gut bacteria have been linked to positive feelings and a better ability to self-regulate emotions.
An obvious sign of slow intestinal transit is constipation: hard, straining bowel movements less than three times a week for at least three months.
According to a 2019 study published in The American Journal of Gastroenterology, one in three people in the United Kingdom who do not believe they are constipated actually meet the medical definition of constipation.
And you may have a slow bowel transit time without meeting the full definition of constipation: You may have regular bowel movements, but they take longer, causing discomfort or bloating.
Scientific studies tend to use expensive high-tech tools; for example, ingestible capsules with sensors that track how long it takes food to travel through the intestine and then transmit precise data to an external device. But there are some ways to measure intestinal transit time at home for free (although keep in mind that they are not diagnostic tests).
In our research, we used bright blue muffins, dyed with food dye, and measured the time between when participants ate them and when they noticed their stools changing color.
You can try this at home by making your own blue muffins, or instead, you can eat sweet corn (easy to spot in stool) or beets (which can turn your poop red).
The good news is that your diet can help you achieve optimal digestion speed so you feel fuller and more energetic for longer, limiting bloating and digestive discomfort. Here are my tips on the best foods that can help.

Blue muffins can help measure a person’s intestinal transit times. They can be easily prepared by adopting a muffin recipe and adding blue food coloring.
SMALL BUT MIGHTY KIWI
Kiwi increases water and volume in the intestine due to its fiber that retains water and helps soften stools and improve bowel movements.
A large study published in The American Journal of Gastroenterology in 2023 found that eating two kiwis a day for a month helped improve constipation and digestive discomfort, adding about 1.5 more bowel movements per week.
A 2010 study, published in the Asia Pacific Journal of Clinical Nutrition, found that eating two kiwis a day reduced intestinal transit time in people with constipation by an average of eight hours.
THE NATURAL FIBER SUPPLEMENT
Psyllium husk is a fiber supplement that you can easily find in most pharmacies and is widely available in powder or capsule form (for dosage, follow the manufacturer’s guidelines).
Made from the seeds of the shrubby herb Plantago ovata, it is packed with a type of fiber that absorbs water in the intestine and helps regulate bowel movements.
Whether you are struggling with constipation or loose stools, psyllium can help soften stool to make it easier to pass or increase its volume to slow the process.

A large study published in The American Journal of Gastroenterology in 2023 found that eating two kiwis a day for a month helped improve constipation.

Rye bread is richer in dietary fiber than other cereals and can speed up intestinal transit time
DARKNESS WITH YOUR BREAD
Rye is higher in dietary fiber than other grains, and rye bread has been shown to speed up slow intestinal transit time by 23 percent compared to white bread, adding 1.4 extra bowel movements per week and reducing levels of compounds that could be linked to colon cancer, according to a 2010 study in the Journal of Nutrition.
Just 100 g of whole wheat rye bread contains 7 g of fiber, which contributes a significant amount to the recommended 30 g.
DRIED FRUITS WITH ADDED PUNCH
You’re probably familiar with the idea that nuts help “maintain regularity” as a concentrated source of fiber. And some dried fruits have specifically been shown to help.
A 2016 study in the Asia Pacific Journal of Clinical Nutrition found that eating 300g of fig paste (if you can’t get it, try a similar amount of dried or fresh figs) daily for two months had a small but positive effect on constipation (although that’s obviously a lot of figs, so you may want to try other strategies first).
Raisins could also be helpful: A small 2013 study, published in the British Journal of Nutrition, found that 120g of raisins a day not only improved participants’ intestinal transit time by 14 hours, but also had levels higher short chain fatty acids. , beneficial molecules produced by the intestinal microbiome.
…AND DON’T FORGET TO KEEP YOURSELF WITH HYDRATED WATER (that includes tea and coffee)
This softens the stool, making it easier for the intestinal muscles to move food at a healthy pace.
While eight glasses of water a day may be a helpful guideline, your hydration needs may vary depending on exercise and weather.
A simple way to check this is by observing the color of your urine; It should be a pale lemonade color.