Summary: Could the bacterial community in your gut influence how you respond to sudden stress? New research from the University of Vienna provides evidence that variations in the human gut microbiome are linked to acute stress reactivity in healthy adults.
The study found that people with greater gut microbial diversity tended to show stronger hormonal and subjective responses to an acute stressor. Rather than indicating vulnerability, this heightened reactivity may reflect a biologically flexible and adaptive stress system. The findings also point to specific microbial metabolic capacities—particularly the ability to produce short-chain fatty acids (SCFAs) like butyrate and propionate—as contributors to individual differences in stress responses.
Key Facts
- Novel human evidence: While animal experiments have suggested a gut–brain connection for stress, this study is among the first robust investigations showing an association between gut composition and acute stress reactivity in healthy humans.
- Rigorous methods: Researchers combined a standardized laboratory stress protocol with stool microbiome profiling and repeated saliva measurements of cortisol, alongside assessments of perceived stress.
- Diet and lifestyle relevance: Because diet and lifestyle shape microbial diversity, they could indirectly influence how people respond to everyday stressors.
- Therapeutic potential: Modulating the microbiome through targeted dietary changes or prebiotics may eventually offer strategies to support stress regulation and mental well-being.
Source: University of Vienna
Background: The gut microbiome— the ecosystem of microorganisms in the digestive tract—plays roles in metabolism, immunity, and communication with the brain via multiple pathways. Prior work in animals has shown that gut microbes can influence stress responses, but whether natural differences in human gut communities relate to acute stress reactivity remained uncertain.
Researchers Thomas Karner, Isabella Wagner, David Berry, and Paul Forbes from the Faculty of Psychology and CeMESS at the University of Vienna examined this question by bringing healthy adult volunteers into the lab. Participants were assigned to either a standardized acute stress procedure or a matched non-stress control task. The team collected baseline stool samples for microbiome analysis, repeated saliva samples to measure cortisol dynamics, and subjective stress ratings throughout the protocol.
Main findings
The primary result was that higher gut microbial alpha diversity correlated with stronger cortisol responses and higher reported stress during the acute stress test. Greater diversity in the gut microbiome is commonly interpreted as a more stable and functionally flexible ecosystem, which may support appropriate activation of physiological stress systems when needed.
In addition to diversity metrics, inferred microbial metabolic capacities were linked to stress reactivity. A higher predicted capacity for bacterial butyrate production was associated with increased stress responsiveness, while a higher predicted capacity for propionate production related to lower responsiveness. Both butyrate and propionate are prominent SCFAs produced by gut bacteria; they influence metabolic and immune processes and can signal to the brain by multiple routes. These contrasting associations suggest a nuanced relationship between specific microbial metabolites and how the human stress system reacts.
As the study authors emphasize, a stronger acute stress response is not inherently harmful. Effective and timely activation of the stress system enables adaptive responses to threats and challenges. Problems tend to arise when the stress system cannot downregulate after activation. The observed links between microbial diversity, SCFA production potential, and stress reactivity point to mechanisms by which the gut ecosystem could contribute to healthy stress regulation.
Key Questions Answered:
A: In this study, higher microbial diversity correlated with greater acute stress reactivity, which can reflect a responsive and adaptable stress system. The crucial issue is not the immediate reaction but the ability to return to baseline afterward.
A: Fiber supports the growth of bacteria that produce SCFAs such as butyrate and propionate. While dietary changes are unlikely to alter responses overnight, sustained improvements in diet that increase microbial diversity may help the body regulate stress hormones more effectively over time.
A: Both SCFAs are beneficial but act via distinct pathways and receptors. Their divergent associations with stress reactivity underscore the complexity of microbiome–brain interactions and the importance of microbial balance rather than focusing on a single metabolite.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The original journal paper was reviewed in full by editorial staff.
- Additional explanatory context was added to aid reader understanding.
About this stress research news
Author: Theresa Bittermann
Source: University of Vienna
Contact: Theresa Bittermann – University of Vienna
Image: The image is credited to Neuroscience News
Original Research: Open access. “Gut microbial diversity and inferred capacity to produce short-chain fatty acids are associated with acute stress reactivity in healthy adults” by Thomas Karner, Paul A.G. Forbes, David Berry, and Isabella C. Wagner. Neurobiology of Stress. DOI: 10.1016/j.ynstr.2026.100807
Abstract
Gut microbial diversity and inferred capacity to produce short-chain fatty acids are associated with acute stress reactivity in healthy adults
Acute stress triggers the release of hormones such as cortisol, facilitating adaptive responses and subsequent recovery. Animal studies indicate that the gut microbiome can modulate stress reactivity, but human evidence has been limited. This study analyzed data from 74 healthy adults who completed a laboratory protocol in which participants were exposed either to a validated acute stress intervention or to a non-stress control task (n = 35 stress, 39 control).
Baseline stool samples were profiled using 16S rRNA gene amplicon sequencing to characterize gut microbial composition. Cortisol changes were measured from repeated saliva samples and paralleled by subjective stress ratings. Results showed that higher gut microbial alpha diversity was associated with greater cortisol and subjective stress reactivity in the stress group but not in controls. Cortisol responses also related to the relative abundance of bacterial taxa inferred to carry metabolic pathways for producing butyrate and propionate, two key SCFAs. These findings highlight a link between microbial diversity, inferred SCFA production capacity, and acute stress responses in healthy adults, supporting a role for the microbiota in flexibly modulating human psychophysiology after stress.