Millions of people struggle with low energy, persistent worry, and a general sense of feeling “off” — but not bad enough to seek clinical help. They are told to sleep more, exercise, or simply “relax.”
A new trial suggests that the solution might reside not in the mind alone, but deep within the gut.
A study has found that specific strains of beneficial bacteria — and even their heat-inactivated versions — can significantly improve vitality (energy levels), reduce perceived stress, and enhance social functioning in healthy adults experiencing mild anxiety.
This research is among the first to test both live probiotics and “postbiotics” (inactivated bacteria) head-to-head in a non-clinical population. The results open an exciting new frontier for mental wellness: one where dietary supplements could offer a safe, accessible way to support emotional resilience and daily energy.
The Study: A Rigorous Look at the Gut-Brain Connection
The gut-brain axis is the biochemical signaling superhighway between the central nervous system and the enteric nervous system. For years, animal studies have shown that altering gut bacteria can change behavior. But high-quality human trials have been scarce, especially in people without diagnosed psychiatric disorders.
This new trial, led by researchers at ADM Health & Wellness and Atlantia Food Clinical Trials, sought to change that.
The study was conducted in two parts:
- Part I (Randomized Controlled Trial): 100 healthy adults with self-reported anxiety were randomly assigned to receive either a daily dose of a live probiotic blend (Bifidobacterium longum CECT 7347 and Lactobacillus rhamnosus CECT 8361) or an identical placebo for 12 weeks. Neither the participants nor the researchers knew who was getting what until the end.
- Part II (Pilot Feasibility Study): A subset of eight participants who did not respond to the placebo in Part I were then given a heat-inactivated (postbiotic) version of the same bacterial strains for 6 weeks. This tested whether even “dead” beneficial bacteria could have psychological effects.
The primary outcome was the Hamilton Anxiety Rating Scale (HAM-A), a clinician-rated measure of anxiety severity. Secondary outcomes included self-reported mood, stress, sleep, quality of life, gastrointestinal symptoms, and even salivary cortisol (a stress hormone) and gut microbiome composition.
The Results: Surprises and Encouraging Signals
Here is where the story gets interesting. The live probiotic blend did not significantly reduce overall anxiety scores on the HAM-A or on standard stress scales. The primary endpoint was not met.
But that is far from the whole story. When the researchers dug deeper, they found several clinically meaningful signals that point to real benefits.
First, vitality improved significantly. Participants taking the live probiotics reported a marked increase in their energy levels, measured by the vitality domain of the 36-item Short Form Survey (SF-36), compared to those taking the placebo (p = 0.017). This is not a trivial finding. Low vitality (fatigue, lack of energy) is one of the most common complaints in primary care and is strongly linked to reduced quality of life.
Second, anhedonia — the inability to feel pleasure — trended toward improvement. Anhedonia is a core symptom of depression and burnout, often resistant to treatment. The study found that participants on the live probiotics had a significant reduction in anhedonia scores (p = 0.045) compared to placebo. This suggests the gut bacteria might be influencing the brain’s reward circuitry.
Third, depressive symptoms showed a trend toward reduction. Total scores on the Patient Health Questionnaire-9 (PHQ-9), a standard measure of depression severity, decreased more in the probiotic group than the placebo group, although this narrowly missed statistical significance (p = 0.089). The pattern was consistent and promising.
Fourth, the postbiotic (inactivated bacteria) also showed benefits. In the small group of placebo non-responders who then received the heat-inactivated version for 6 weeks, researchers saw significant within-group improvements in:
- Vitality (p = 0.006)
- Social functioning (p = 0.010)
- Perceived Stress Scale (PSS) scores (p = 0.050)
This is a crucial finding. It suggests that you do not necessarily need live, colonizing bacteria to get a mental health benefit. The metabolic products and cell wall components of the bacteria — the postbiotics — may be sufficient to signal the gut-brain axis.
What Happened in the Gut?
To understand why these changes occurred, the researchers analyzed the participants’ gut microbiomes. They made two striking observations.
First, the live probiotic blend helped preserve butyrate-producing bacteria. Butyrate is a short-chain fatty acid that is the primary fuel for colon cells. It also has powerful anti-inflammatory properties and has been linked to reduced stress and improved mood. Specifically, the study found that supplementation preserved members of the Pseudoflavonifractor genus and the Clostridium SGB6179 species. In contrast, these beneficial bacteria declined in the placebo group.
Second, the abundance of Bifidobacterium longum (one of the administered strains) was inversely associated with perceived stress. In other words, participants whose guts had higher levels of B. longum tended to have lower scores on the Perceived Stress Scale. This correlation provides direct evidence that the supplemented bacteria were active and linked to the psychological outcome.
Why This Matters for You
If you are a healthy adult who feels “tired and wired” — drained of energy but unable to relax — this study offers a new, low-risk option to consider.
Unlike prescription medications for anxiety or depression, which can have significant side effects and require a clinical diagnosis, probiotics and postbiotics are generally recognized as safe. They are available over the counter. And this trial suggests that even if they do not dramatically lower your anxiety score, they might give you back your energy, help you feel more pleasure, and improve your social life.
Key Benefits of the Live Probiotic Blend (vs. Placebo)
| Outcome Measure | Effect | Statistical Significance |
|---|---|---|
| Vitality (Energy Levels) | Significant Improvement | p = 0.017 |
| Anhedonia (Pleasure) | Significant Improvement | p = 0.045 |
| Depressive Symptoms (PHQ-9) | Trend Toward Improvement | p = 0.089 |
| Overall Anxiety (HAM-A) | No Significant Effect | Not met |
*Data from Day et al., Brain Sciences 2026, 16, 419. Based on 12-week supplementation with B. longum CECT 7347 and L. rhamnosus CECT 8361.*
Benefits of the Postbiotic (Inactivated) Blend (Within-Group Changes from Baseline)
| Outcome Measure | Improvement | Statistical Significance |
|---|---|---|
| Vitality (SF-36) | Significant | p = 0.006 |
| Social Functioning (SF-36) | Significant | p = 0.010 |
| Perceived Stress (PSS) | Significant | p = 0.050 |
*Data from Day et al., 2026. Six-week supplementation with heat-inactivated B. longum and L. rhamnosus in placebo non-responders.*
Live Probiotics vs. Postbiotics: What Is the Difference?
You might be wondering: should I take live probiotics or postbiotics?
Traditional probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit. They need to survive stomach acid and colonize, at least temporarily, the gut.
Postbiotics are a newer concept. They are preparations of inanimate microorganisms and/or their components that confer a health benefit. Because they are not alive, they are more stable, have a longer shelf life, and may be safer for immunocompromised individuals. This study is exciting because it shows that even heat-killed bacteria — which cannot colonize the gut — can still improve mood and energy. This suggests that the benefits are mediated by bacterial components (like cell wall polysaccharides) or metabolites present even after killing.
The Limitations: A Pilot, Not a Panacea
As with any good science, it is essential to be honest about the limitations.
First, the primary outcome was negative. The probiotics did not significantly reduce anxiety as measured by the HAM-A. If you are looking for a powerful anti-anxiety treatment, this is not it.
Second, the postbiotic part of the study was very small (only 8 participants) and had no placebo control. Those results are encouraging but preliminary. They need to be confirmed in a larger, fully controlled trial.
Third, the study population was healthy adults with “self-reported anxiety,” not diagnosed anxiety disorders. We do not know if the effects would be larger or smaller in people with clinical depression or generalized anxiety disorder.
Fourth, the trial was funded by ADM, a company that produces and sells probiotic ingredients. While the study design was rigorous (randomized, double-blind, placebo-controlled), industry funding always warrants a careful look at potential conflicts of interest.
The Takeaway: A New Tool for the Wellness Toolkit
This study does not prove that probiotics cure anxiety. But it does provide strong, preliminary evidence that specific bacterial strains — Bifidobacterium longum CECT 7347 and Lactobacillus rhamnosus CECT 8361 — can:
- Boost energy and vitality
- Improve the ability to feel pleasure
- Reduce perceived stress
- Enhance social functioning
And remarkably, these benefits appear even with heat-inactivated (postbiotic) versions of the same strains.
For the millions of people struggling with subclinical anxiety, low energy, and daily stress — who do not meet the criteria for a psychiatric diagnosis but still suffer — this is welcome news. It suggests that a simple, safe, dietary supplement could be part of the solution.
The gut-brain axis is real. And we are just beginning to learn how to talk to it.
The next time you feel your energy flagging and your stress rising, remember: the conversation between your gut and your brain might be the most important one you are not having. And you might be able to start it with a probiotic.
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