Summary: Individual differences in gut physiology and the gut environment strongly influence the composition and activity of the gut microbiome and how we process food. Using a small wireless capsule that recorded pH, temperature and pressure as it traveled through the digestive tract, researchers observed large variations in transit times and local gut conditions between people. These variations affect where and how nutrients are absorbed, which compounds reach the large intestine for microbial fermentation, and which bacterial species thrive—providing important insights for more personalized nutrition strategies.
By mapping how the gut environment varies from person to person, scientists hope to develop dietary recommendations tailored to individual gut function. The study highlights that no two digestive tracts are the same, making personalized approaches essential for improving metabolic and digestive health.
Key Facts:
- The study used a smart wireless capsule to record gut pH, temperature and pressure as it moved through the digestive tract.
- Large inter-individual differences in pH and intestinal transit time affect nutrient absorption, microbial fermentation and metabolite production.
- Results support the idea of personalized dietary strategies based on individual gut physiology and environment.
Source: University of Copenhagen
A new study from the Department of Nutrition, Exercise and Sports at the University of Copenhagen expands our understanding of gut physiology and the lives of gut bacteria.
The research demonstrates that shifts in the gut environment—such as pH and transit time—are linked to differences in microbial composition and metabolic activity. These environmental features help explain why people harbor different gut bacteria and why they may respond differently to the same foods.
A voyage of discovery through the gut
In 2021, 50 healthy volunteers swallowed a capsule roughly the size of the outer joint of a thumb while eating a standardized breakfast. The capsule recorded pH, temperature and pressure as it passed through the stomach, small intestine and large intestine, and it was recovered in the stool between 12 and 72 hours later. From these recordings the researchers discovered pronounced differences in local gut conditions and travel times between participants.
For example, transit through the small intestine ranged from about 2 hours in some people to as long as 10 hours in others. Because most nutrient absorption occurs in the small intestine, that range implies significant variation in how much dietary material is absorbed before it reaches the large intestine, where resident microbes ferment remaining substrates.
Previously, many studies inferred gut activity from stool samples and dietary records. The wireless capsule provides a continuous, segment-specific view of the gut environment, offering more precise information about how pH and transit vary along the digestive tract and how those variations correlate with microbial composition and metabolic output.
“The capsule lets us collect data that help explain individual differences in digestion, nutrient uptake and bowel habits,” says Associate Professor Henrik Roager, who led the study. “This gives us much richer insight than what we could obtain from diet records and stool alone.”
The gut environment: from acidic stomach to alkaline small intestine and changing colon
As the capsule passed into the stomach, it detected very low pH values caused by stomach acid that begins food breakdown. When the contents entered the small intestine, secreted bicarbonate neutralized the acid and created a more alkaline environment where most nutrient absorption takes place.
Indigestible residues then moved into the large intestine, where microbes fermented carbohydrates and other substrates. Microbial fermentation produces short-chain fatty acids that lower pH in the proximal colon; as these acids are absorbed and microbial activity shifts, pH gradually rises along the length of the colon.
The capsule registered these pH transitions, allowing researchers to estimate how long food remained in each gut segment. Because pH is a key determinant of microbial growth and metabolism, the team observed clear associations between segmental pH/transit and differences in microbiome composition and metabolite profiles.
“Environmental conditions inside each person’s gut help explain why gut bacterial communities differ between people,” says Henrik Roager.
Toward personalized nutrition
The findings have implications for dietary guidance and personalized nutrition. “Our results make it clear that we are unique—not only in genetics and lifestyle, but also in gut function,” says Henrik Roager. “We often assume everyone digests and absorbs food the same way, but that is not always true. Differences in the gut environment can shape how individuals respond to the same diet.”
Recognizing segmental transit times and local pH differences could improve dietary recommendations by accounting for which nutrients reach the colon, how they are fermented, and which microbial-derived metabolites are produced—factors that influence metabolic and gut health.
Facts about the study
The capsules used by the 50 participants measured 26 x 13 mm. Each participant swallowed the capsule with a standardized breakfast composed of rye bread with butter and jam, a boiled egg, a serving of plain yoghurt with nuts and blueberries, and a glass of water.
The study was led by Nicola Procházková during her PhD and postdoctoral work at the Department of Nutrition, Exercise and Sports, University of Copenhagen (2020–2024). The research was conducted in collaboration with DTU Food and KU Leuven, Belgium, and forms part of the PRIMA Challenge project. Funding was provided by the Novo Nordisk Foundation.
The study is published as “Gut physiology and environment explain variations in human gut microbiome composition and metabolism” in the journal Nature Microbiology.
About this microbiome research news
Author: Kristian Madsen
Source: University of Copenhagen
Contact: Kristian Madsen, University of Copenhagen
Image: The image is credited to Neuroscience News
Original Research: Open access. “Gut physiology and environment explain variations in human gut microbiome composition and metabolism” by Henrik Munch Roager et al., Nature Microbiology.
Abstract
Gut physiology and environment explain variations in human gut microbiome composition and metabolism
The human gut microbiome is highly individual. Yet the impact of gut physiology and local environmental factors on microbiome variation is not fully understood. In this observational study, researchers used multi-omics profiling over nine consecutive days in 61 healthy adults and measured whole-gut and segmental transit time and pH with a wireless motility capsule in 50 participants.
They found notable daily fluctuations within individuals and substantial differences between individuals. Within-person microbiome and metabolic changes correlated with stool moisture and faecal pH. Between-person differences were linked to whole-gut and segmental transit times and pH. Metabolites from microbial carbohydrate fermentation correlated negatively with passage time and pH, while proteolytic metabolites and breath methane correlated positively. Associations were also identified between segmental transit time/pH and a range of diet-, host- and microbe-derived metabolites.
Overall, the study supports the conclusion that gut physiology and environmental conditions are key to understanding individual differences in human gut microbiome composition and metabolism.