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Science
Ecosystem — Most people know that fibre is good for your digestion. Now, new research shows that our gut microbiomes are so different that we may need to tailor diets to individual digestion times and pH levels.
Fifty participants began their day with a seemingly normal breakfast — rye bread with butter and marmelade, a boiled egg, a portion of natural yoghurt with nuts and blueberries and a glass of water. And a capsule.
On its journey through the digestive system, the capsule recorded important information about pH levels, pressure, and temperature in the participants’ intestinal environment. The results were surprising.
It is generally assumed that gut environments are pretty much the same. But the capsule’s journey revealed that they are actually unique from person to person, explains Henrik Munch Roager, who is associate professor at the Department of Nutrition, Exercise and Sports. The capsule plays a key role in a new study.
Facts
In 2021, fifty healthy participants swallowed a capsule every morning, which collected information on pH, temperature, and pressure as it passed through the stomach, small intestine, and large intestine.
The study was published in Nature Microbiology and led by Nicola Procházková, a PhD student and postdoc at the Department of Nutrition, Exercise and Sports at UCPH from 2020 to 2024. The research was funded by the Novo Nordisk Foundation.
The capsules took anywhere from 12 to 72 hours to complete their journey through the participants’ digestive systems. The transit through the small intestine took anything from two to ten hours, while the transit through the large intestine took anything between two and 63 hours, according to Henrik Munch Roager.
The differences in travel times underscore the uniqueness of the gut environments, and this could have a significant impact on both nutrient absorption and the conditions for gut bacteria:
»The small intestine is where we digest food and absorb most of the nutrients. So, whether food has two or ten hours to be digested and absorbed into the bloodstream could affect how much nutrition is absorbed in the small intestine and how much continues to the large intestine,« says Henrik Roager and continues:
»And the amount of time food spends in the large intestine also affects the types of gut bacteria present and their activity.«
Besides the varying travel times, the study made another crucial discovery: Gut environments have unique pH or acidity levels. This has not previously been studied in humans, making it particularly interesting to track the capsule’s journey through the digestive system’s pH rollercoaster, according to Henrik Roager:
»What stands out is that when we measure pH levels in healthy individuals, we see that the values vary greatly between different parts of the intestine from person to person. In the small intestine, pH levels ranged between 6.5 and 8.5. That might sound like a small difference of two, but it’s important to remember that pH operates on a logarithmic scale, making this a significant variation.«
If you eat a very limited diet with no fibre, you are essentially starving your gut bacteria.
Henrik Roager, associate professor at the Department of Nutrition, Exercise and Sports
As food moves through the digestive system, it first enters the acidic stomach, where it is broken down by stomach acid and digestive enzymes. From there, it enters the small intestine, where the acidic food is neutralised and new digestive enzymes take over, allowing nutrients to be absorbed. Finally, the remaining indigestible food reaches the large intestine, where it is fermented by gut bacteria.
The relevance of this new discovery is significant, as pH levels influence many important bodily processes:
»The activity of digestive enzymes is influenced by pH, the absorption of nutrients is influenced by pH, and the growth and activity of gut bacteria are influenced by pH. So, we are dealing with an environmental factor that likely affects how we digest food and which bacteria can thrive and how active they are,« says Henrik Roager.
According to Henrik Roager, the unique intestinal environment can be compared to an ecosystem:
»It’s similar to any ecosystem where environmental conditions dictate which species thrive. Such an ecosystem can be resilient to stress and challenges, but we imagine that it could also collapse if the environmental conditions in the gut are challenged or change over a period of time.«
Repeated antibiotic treatments or a very one-sided diet with little fibre are examples of things that challenge the gut ecosystem. Dietary fibre is crucial for impoverished gut biomes:
»We know that bacteria prefer to break down dietary fibre, but when they run out of fibre, they start breaking down proteins instead. This leads to the production of substances believed to be harmful,« says Henrik Roager and continues:
»If you eat a very limited diet with no fibre, you are essentially starving your gut bacteria, and over time you will select for fewer bacteria capable of surviving in that environment.«
People are currently left to experiment on themselves with different foods.
Henrik Roager, associate professor at the Department of Nutrition, Exercise and Sports
It’s essential to create good conditions for gut bacteria, as they contribute to extracting additional energy from food, producing vitamins, stimulating the release of appetite-regulating hormones, and providing fuel for intestinal cells, which interact with both the nervous system and the immune system, explains Henrik Roager.
This is where the study’s findings on travel time become particularly relevant:
»In cases of very long travel time, bacteria gradually run out of dietary fibre and start breaking down proteins in the lower part of the large intestine. Ensuring that bacteria have enough dietary fibre could, for example, help prevent constipation.«
The study’s striking findings provide valuable insight into why people react differently to the same diet, potentially explaining the digestive issues many experience:
»We really want to understand how we can alleviate the digestive issues that many people struggle with, whether it’s constipation, bloating, or stomach pain,« says Henrik Roager.
The pH levels in different parts of the intestine vary greatly from person to person.
Henrik Roager, associate professor at the Department of Nutrition, Exercise and Sports
If, for example, someone struggles to produce stomach acid, their risk of infections will be higher, and they will be less able to break down proteins in meat, explains Henrik Roager. It is also conceivable that the number of calories absorbed by the body and excreted in stools could vary from person to person depending on their gut environment – a question Henrik Roager and his colleagues are already investigating.
A diet more tailored to an individual’s unique gut environment could ultimately improve quality of life:
»At the moment, people are largely left to experiment with different foods on their own. By understanding how gut environments vary from person to person, we hope to start tailoring diets to reduce symptoms and improve overall well-being,« says Henrik Roager.