Plate Nº 76 · recorded October 10, 2026
Biology & EvolutionReported finding
Diet Alone Can't Explain Why Gut Microbes Differ Worldwide
A Nature Microbiology study shows fiber boosts Segatella copri only with help from E. coli, so diet alone can't explain global gut microbiome differences.
By Nathan Brooks4 min read766 words
In brief
- The study was published in Nature Microbiology in 2026 (DOI: 10.1038/s41564-026-02500-6).
- The team screened 94 dietary components against a defined community of 21 human gut bacteria; more than half promoted growth of Segatella copri.
- S. copri gained an advantage from the plant fiber arabinan only when E. coli or related Enterobacteriaceae were present in the community.
- Analysis of microbiome data from about 1,000 healthy adults confirmed S. copri and Enterobacteriaceae were more common in nonindustrialized populations.
- Researchers propose sugars released during arabinan breakdown act as signal molecules, though the exact mechanism remains unknown.
Fiber is not enough. A new study published in Nature Microbiology (2026) shows that diet alone cannot explain why gut microbiomes differ between people from industrialized and nonindustrialized regions — the bacteria already living in the gut, and how they interact, matter just as much.
Researchers at the Helmholtz Center for Infection Research (HZI), working with the European Molecular Biology Laboratory (EMBL), the University of Trento and the University of Tübingen, found that plant-based dietary fiber shifts the competitive balance in favor of Segatella copri, a bacterium particularly common in nonindustrialized populations. But that shift happened only under certain conditions, depending on which other bacteria were present.
Why did scientists question the diet explanation?
The gut microbiome is the community of microorganisms living in our intestines. Researchers have long known that its composition differs across regions: Bacteroidaceae bacteria dominate in industrialized populations, while Prevotellaceae — a family that includes S. copri — appear more frequently in many nonindustrialized populations.
A plant-rich diet has been a popular proposed explanation for this pattern. The new work suggests the story is more complicated.
"We wanted to understand which factors actually influence the competition between these bacteria in the gut," says Dr. Caroline Tawk, one of the study's first authors, who until recently worked in the department of professor Till Strowig at HZI. She spent several months at EMBL in Heidelberg developing a highly parallelized experimental setup to test a wide range of dietary components.
How did the team test 94 dietary components?
The researchers assembled a defined community of 21 human gut bacteria in the lab. Against this community, they screened 94 dietary components, focusing on complex carbohydrates and vitamins. More than half of the components promoted the growth of S. copri within the community.
One component stood out: arabinan, a carbohydrate found in plant cell walls. The team examined it in detail. Both S. copri and Bacteroidaceae can directly utilize arabinan, so a simple nutritional advantage could be ruled out as the reason S. copri expanded.
Then came the surprise. The advantage disappeared in simpler setups.
"When we brought S. copri and Bacteroidaceae together without the other members of the gut community, S. copri did not prevail despite the presence of arabinan," Tawk explains. "Only when we added Escherichia coli to the mix did the competitive balance shift in favor of S. copri."
Other Enterobacteriaceae tested, including Klebsiella and Salmonella, also supported S. copri under certain conditions. Notably, even E. coli strains that cannot metabolize the monosaccharides produced during arabinan breakdown boosted S. copri growth.
What does that mean for how bacteria cooperate?
The findings point to an unexpected mechanism. Because helpful E. coli strains cannot consume the sugars in question, sugar consumption cannot explain the effect.
"We therefore assume that the presence of the sugars as signal molecules — rather than their consumption by E. coli — may be sufficient to explain the observed supportive effect," says Dr. Youssef El Mouali, another first author of the study. The exact molecular mechanism, however, remains unknown — an important caveat for this still-preliminary line of research.
In plain terms: the sugars released when fiber breaks down may act like chemical messages that change bacterial behavior, rather than food that fuels growth.
Do the lab results hold in real human guts?
To check, the HZI team joined forces with researchers at the University of Trento and analyzed publicly available microbiome data from roughly 1,000 healthy adults.
The results echoed the laboratory findings:
- S. copri and Enterobacteriaceae were more common and more diverse in data sets from nonindustrialized populations.
- Within those populations, a higher number of different Enterobacteriaceae species was associated with a higher proportion of S. copri.
This suggests the supportive effect occurs not only in controlled lab conditions but also in the human gut. Still, the data are observational, so they show an association rather than proven cause and effect.
What comes next?
The study's central lesson is about context. A dietary component cannot be evaluated in isolation from the bacterial community that receives it.
"Our results show that the effect of a dietary component should not be considered in isolation from the existing bacterial community," study leader Strowig summarizes. "We need to clarify in further studies whether this knowledge can be used for personalized dietary or microbiome approaches."
Whether these insights will eventually translate into tailored diets or microbiome-based therapies remains an open question for future research.
Publication details: Caroline Tawk et al., "Synergy between Enterobacteriaceae and diet mediates competition between dominant Bacteroidales in the human gut," Nature Microbiology (2026). DOI: 10.1038/s41564-026-02500-6
via Phys.org Biology (Source)
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