Ashhar Alam/New Delhi

A new study has suggested that a higher diversity of gut bacteria may be linked to stronger hormonal and stress responses in humans, highlighting the complex role of the gut microbiome in regulating the body’s reaction to stress.

The gut microbiome, comprising trillions of microorganisms living in the digestive tract plays a key role in metabolism, immunity, and overall health. Researchers now believe it may also influence how the body responds to stressful situations.

The study noted that a more diverse microbial ecosystem is generally considered healthier and more resilient. However, it also found that in some cases, greater bacterial diversity was associated with heightened stress reactivity, both in terms of stress hormones like cortisol and subjective perception of stress.

Lead researcher Thomas Karner from the University of Vienna explained that a stronger stress response is not necessarily harmful. According to him, proper activation of the body’s stress system helps individuals adapt to challenges effectively. He added that gut bacteria and their metabolic byproducts could support this adaptive mechanism.

Published in the journal Neurobiology of Stress, the research is among the first to demonstrate a clear link between gut microbiome diversity and acute stress responses in healthy adults.

The study involved 74 participants who were either exposed to a standardized stress test or a non-stress control task. Researchers measured cortisol levels in saliva, recorded self-reported stress, and analyzed stool samples to examine gut bacteria composition and their metabolic potential.

Findings showed that higher microbial diversity was associated with increased cortisol levels and perceived stress among participants exposed to stress. The study also observed associations between stress reactivity and bacterial metabolites such as short-chain fatty acids, including butyrate and propionate, which are known to influence metabolism, immunity, and brain function.

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While higher butyrate-producing capacity was linked to stronger stress responses, propionate production appeared to have the opposite effect, reducing stress reactivity.

Researchers concluded that the relationship between gut bacteria and stress is highly complex and cannot be explained in simple terms, suggesting that diet and lifestyle may also play an important role in shaping this interaction.