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 might surprise you, but in fact, research (including my own) shows that intestinal transit time – the time it takes from eating a food to being digested and excreted as waste – can be linked to health problems.
Think of your instinctive transit time like a train ride: If the train crawls or stays in a station too long, everything moves backwards, causing delays and discomfort. But if the train passes through stations too quickly, it misses important stops where passengers need to get off.
For example, according to a study published in the British Journal of Cancer in 2004, a slow intestinal transit time is associated with a higher risk of colon cancer – perhaps because it prolongs the exposure of the intestinal wall to potential carcinogens present in stools.
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 were previously associated with markers of poor 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 present in the gut).
Although this is not harmful in itself, it can have negative consequences under certain conditions. Normally, microbes present in the intestine are excreted in the stool. But when transit times are slow, they are not eliminated and continue to multiply.
Registered dietitian Emily Leeming explains that intestinal transit time – the time it takes between eating a food and digesting it and excreting it as waste – can be linked to health problems.
This creates more microbes to feed on, while their food source, primarily fiber, becomes scarcer as it takes longer to reach them. Microbes can then end up producing harmful byproducts linked to inflammation, which is often a precursor to disease.
(This is one of the reasons why I advise people to eat more fiber – with 90% of the UK population failing to meet the recommended 30g of fiber a day) – don’t forget to drink enough fluids too. )
But a rapid intestinal transit time can also cause problems. Food moving through the gut too quickly can cause less absorption of nutrients, leading to energy losses and leaving you 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 you against infections or are linked to mood) – this is because rapid transit limits the time it takes for bacteria to interact with the foods you eat. , and produce the molecules that support your well-being.
Although occasional episodes 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 danger, frequent events can leave you tired, bad mood or sick. .
The sweet spot for digestion is thought to be between 14 and 58 hours. This is long enough for nutrients to be absorbed, but not so long that your gut microbes start to miss their preferred food source.
This balance supports a “healthy” gut microbiome, enabling the production of healthy molecules such as short-chain fatty acids that support your immune system as well as the health of your gut.
So how do you measure your intestinal transit time?
Certain gut bacteria have been linked to positive feelings and a better ability to self-regulate emotions
A clear sign of slow bowel movement is constipation – straining, hard stools or less than three times a week for at least three months.
In the UK, up to one in three people who don’t think they’re constipated actually meet the medical definition of constipation, according to a 2019 study published in The American Journal of Gastroenterology.
And you may have slow bowel transit time without meeting the full definition of constipation: You may have regular bowel movements, but they take longer, leading to discomfort or bloating.
Scientific studies tend to use expensive high-tech tools; for example, ingestible capsules with sensors that track the time it takes for food to travel through the intestine and then transmit precise data to an external device. But there are several ways to measure your intestinal transit time at home for free (although, note, these are not diagnostic tests).
In our research, we used bright blue muffins — dyed with food coloring — to measure the time between participants eating 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 beetroot (which can turn your poop red).
The good news is that your diet can help you achieve optimal digestion speed to help you feel full and energized for longer, thereby limiting bloating and digestive discomfort. Here are my tips on the best foods that can help you.
Blue muffins can help measure a person’s intestinal transit times. They can easily be made by co-opting a muffin recipe and adding blue food coloring.
SMALL BUT POWERFUL KIWI
Kiwi increases water and volume in the intestine with its water-retaining fiber which helps soften stools and improve bowel movements.
A large study published in the American Journal of Gastroenterology in 2023 found that eating two kiwis per day for a month helped improve constipation and digestive discomfort, adding about 1.5 extra 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.
NATURAL FIBER SUPPLEMENT
Psyllium husk is a fiber supplement that you can easily find at most pharmacies, widely available in powder or capsule form (for dosage, follow the manufacturer’s directions).
Made from the seeds of the shrubby herb Plantago ovata, it contains a type of fiber that absorbs water in the intestine, helping to regulate bowel movements.
Whether you suffer from constipation or loose stools, psyllium can help by either softening the stool to make it easier to pass or bulking it up to slow things down.
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 higher in dietary fiber than other grains and may speed up intestinal transit time
GET DARK 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% 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 100g of Pumpernickel rye bread contains 7g of fiber, which is a significant amount compared to the recommended 30g.
DRIED FRUITS WITH ADDED PUNCH
You’re probably familiar with the idea of dried fruit helping you “stay regular” as a concentrated source of fiber. And certain dried fruits have specifically been shown to help.
A 2016 study published in the Asia Pacific Journal of Clinical Nutrition found that consuming 300g of fig paste daily (if you can’t get hold of it, try a similar amount of dried or fresh figs) for two month had a small but positive effect on constipation (although that’s obviously a lot of figs, so you might want to try other strategies first).
Raisins might also be helpful: A small 2013 study, published in the British Journal of Nutrition, found that 120g of raisins per day not only improved participants’ intestinal transit time by 14 hours, but they also had higher levels of short-chain fatty acids. , beneficial molecules produced by your intestinal microbiome.
…AND REMEMBER TO STAY HYDRATED WITH WATER (which includes tea and coffee)
This softens the stool, making it easier for your intestinal muscles to move food at a healthy pace.
Although eight glasses of water per day can be a useful guideline, your hydration needs may vary depending on exercise and weather.
An easy way to check is to look at the color of your urine: it should be a pale lemonade color.
