HPC · Science Deep Dive 6 April 2026 · revised 2026-04-06

The Gut-Brain Axis: What the Science Actually Shows About Your Microbiome, Mood, and Focus.

The bacterial ecology in your gut does not merely digest food. It manufactures neurotransmitter precursors, calibrates your stress response, and shapes the inflammatory terrain that determines whether you think clearly or poorly. Here is what the science actually says, and what to do with it.

Section: Bio-Performance
Reading time: 22 min read
Sources: 42 · reviewed

01The Second Brain

500 million enteric neurons were never in the textbooks

You have a nervous system you have probably never thought about. It is not in your skull. It wraps the full length of your gastrointestinal tract: an estimated 200 to 500 million neurons threaded through nine metres of tissue, sensing, signalling, and making decisions without ever consulting the brain above your neck.[31] Neuroscientists call it the enteric nervous system, and for decades it was treated as a local wiring job: useful for peristalsis, irrelevant to cognition. That assumption has not held. The gut-brain axis science of the past decade has shown that this so-called "second brain" is in constant upstream communication with the cortex, the amygdala, and the hypothalamus. The conversation is being brokered by roughly 38 trillion bacteria living in your large intestine.[34][19]

The implications are substantial. A 2022 microbiome-wide association study spanning 2,593 participants across two independent cohorts identified 13 microbial taxa significantly associated with depressive symptoms. These were bacteria involved in synthesising GABA, butyrate, and serotonin precursors.[1] A separate meta-analysis of 44 studies and nearly 5,000 participants found that people with depressive disorder harbour a consistently altered microbial signature: enriched pro-inflammatory species and depleted butyrate producers.[4] These are not fringe findings. They appear in Nature Communications and Translational Psychiatry, describing an axis of influence that most performance-focused people have never heard of.

The question is no longer whether the gut microbiome is associated with mood and cognition. It is how the signal travels, how large the effect is, and what (if anything) you can do about it.

01 · The history

Start with the numbers. Approximately 90% of the body's serotonin (the neurotransmitter most associated with mood regulation) is stored in enterochromaffin cells lining the gut wall.[8][35] That figure is frequently misread. The gut microbiota do not manufacture most of this serotonin themselves. What specific bacterial species do is signal to enterochromaffin cells to upregulate synthesis, an indirect regulatory role, but a functionally significant one.[35][30] The peripheral serotonin pool does not cross the blood-brain barrier directly. Its influence on the brain is routed through vagal afferents and immune signalling, which makes the mechanism more subtle and more systemic than the "gut makes happy chemicals" narrative suggests.[7][9]

More than 50% of the body's dopamine is synthesised in the gastrointestinal tract. The gut microbiota also produce measurable quantities of GABA, norepinephrine, and acetylcholine, all acting on local enteric and vagal receptors before their signals reach the central nervous system.[8][25] On top of that, the gut produces 500 to 600 millimoles of short-chain fatty acids daily: metabolites like butyrate, propionate, and acetate that serve as energy substrates for colonocytes and as signalling molecules that modulate neuroinflammation and blood-brain barrier integrity.[9][11]

02The Mechanism

The Signalling Architecture Behind Gut-Brain Communication

The gut-brain axis becomes clearer once you stop thinking of the microbiome as a single organ. It is a distributed signalling network. The roughly 38 trillion bacteria in your colon, representing more than 1,000 known species, do not communicate with the brain through one pathway.[34][7] They use at least four, and those pathways converge on the same brain structures that regulate mood, stress, and cognitive sharpness.

The first pathway is neural. Neuropod cells in the gut epithelium form direct synaptic connections with vagal afferent fibres, transmitting glutamate signals that reach the brainstem within milliseconds.[29] That is faster than any hormone could travel through the bloodstream. The vagus nerve carries these signals to the nucleus tractus solitarius, which relays them to the hypothalamus, the amygdala, and the prefrontal cortex.[6][42] When the microbiome composition shifts (through diet, antibiotics, or chronic stress), the character of these signals changes.

The second pathway is metabolic. The gut microbiota ferment dietary fibre into short-chain fatty acids at a rate of 500 to 600 mmol per day, in a roughly 60:20:20 ratio of acetate, propionate, and butyrate.[9] Butyrate matters most for the brain. It strengthens the intestinal barrier, reduces translocation of bacterial endotoxins, and in animal models crosses the blood-brain barrier to inhibit histone deacetylases, modulating gene expression in neurons.[11][9] The direct human evidence for SCFAs as cognitive enhancers remains limited, but the mechanistic plausibility is substantial.[10]

When microbial diversity collapses, IL-6 and TNF-alpha flood the bloodstream, then cross the blood-brain barrier to activate microglia, the brain's resident immune cells, locking the cortex into a low-grade neuroinflammatory state.

Diagram · HPC

The third pathway is endocrine. The hypothalamic-pituitary-adrenal axis (the body's central stress-response system) is bidirectionally coupled to the gut microbiome.[10][27] When you experience psychological stress, cortisol rises. Elevated cortisol increases intestinal permeability, allowing bacterial fragments called lipopolysaccharides to leak into the bloodstream.[32] Those fragments trigger systemic inflammation, which further disrupts the microbiome, which further elevates cortisol. Researchers call this the dysbiosis-inflammation-stress cycle. It can sustain itself long after the original stressor has passed.[19][10]

Sudo's 2004 experiment demonstrated this coupling directly: germ-free mice showed exaggerated HPA axis responses to stress compared to conventionally colonised mice, and the effect was partially reversed by introducing a single Bifidobacterium strain.[27] The experiment was in mice. But the principle (that microbial colonisation calibrates the stress response) has since been supported by human evidence showing that probiotic supplementation can attenuate cortisol output in controlled settings.[3]

The fourth pathway is immune. The gut houses approximately 70% of the body's immune tissue, and the microbiome continuously trains immune cells to distinguish friend from threat.[22][41] When microbial diversity drops (a state called dysbiosis), pro-inflammatory cytokines like IL-6 and TNF-alpha increase systemically.[5] Those cytokines cross the blood-brain barrier, activate microglia (the brain's resident immune cells), and produce what immunologists call neuroinflammation: a low-grade inflammatory state associated with depression, cognitive fog, and reduced executive function.[19][24] Gut peptides, including neuropeptide Y and cholecystokinin, add a further layer; they modulate anxiety-related behaviour and immune signalling through receptors distributed across the gut-brain axis.[26][38]

03Evidence

The Five Strongest Studies on the Gut-Brain Axis and Mental Health

01The claim

The single load-bearing finding

The hero study finds 13 taxa.

Pooled estimate

02How we measured

Grading the microbiome studies

Studies scored on design, sample, rigour, causality, replication.

Causal direction is the hardest problem in gut-brain research: microbiome composition correlates with mood, but separating gut-drives-brain from brain-drives-gut requires replication across independent cohorts and designs that can rule out reverse causation.

Rubric weights

Design/35

Sample/20

Rigour/15

Causality/15

Replication/15

03The spread

Heterogeneity across 5 studies

Effect sizes across the ranked studies.

Spread

82 → 72 /100

Range of point estimates across ranked studies.

04What does not hold

Negative knowledge

What the evidence base does not support.

The Wastyk study is practically relevant partly because it produced a null result alongside its positive one. Fermented foods increased diversity and reduced inflammation. High-fibre foods (the dietary intervention most commonly recommended for gut health) did neither.[5] Four immune cell types showed reduced activation in the fermented-food group; eleven microbial carbohydrate-degrading enzymes increased in the fibre group, but this did not translate to immune benefit. That contrast reframes the dietary conversation. Fibre feeds existing microbes but does not reliably diversify the community

Consumer dose

The studies

5 trials. One pooled answer.

Below: the anchor study in full; then the forest plot at scale; then the supporting trials in ranked order.

01Anchor

, Gut microbiome-wide association study of depressive symptoms

Radjabzadeh 2022 MWAS · Independent Replication · Neurotransmitter Biology

The largest microbiome-wide association study of depression ever conducted, spanning 2,593 participants across the Rotterdam Study and the multi-ethnic HELIUS cohort. **Radjabzadeh's team identified 13 bacterial taxa, including genera involved in GABA, butyrate, serotonin

Rubric breakdown

Design22/35

Sample18/20

Rigour13/15

Causality9/15

Replication10/10

Citations10/10

Total 82/100

The strongest studies, ranked by methodological weight.

Each scored 0–100 against a six-criterion rubric, tagged by design and year; the anchor leads.

Anchor (Rank 1) Supporting

Rank Authors & title Journal · Year Finding Score

Asad

, Effects of Prebiotics and Probiotics on Symptoms of Depression and Anxiety in Clinically Diagnosed Samples

· 2024

Across 23 RCTs involving 1,401 clinically diagnosed participants, probiotic supplementation produced a pooled depression reduction of SMD = −0.96 (95% CI: −1.31, −0.61), classified as a large effect, though with substantial heterogeneity (I²=85%) indicating that outcomes vary significantly by strain, dosage, measurement scale, and intervention duration.

79/100

Allen

, Bifidobacterium longum 1714 as a translational psychobiotic

· 2016

A single psychobiotic strain (B. longum 1714) significantly reduced daily stress (Cohen's d=0.53, P=0.03), attenuated cortisol output (P=0.05, r=0.42), altered frontal EEG theta power, and reduced Paired Associate Learning errors (P<0.01) in a crossover design that eliminates between-subject variance.

76/100

Gao

, Gut microbiota composition in depressive disorder: systematic review, meta-analysis, and meta-regression

· 2023

Across 4,883 participants (2,091 patients, 2,792 controls), medication-free depressive patients showed significantly decreased Firmicutes (SMD: −1.54), while depressive disorder was characterised by enriched pro-inflammatory bacteria (Eggerthella, Enterococcus, Flavonifractor) and depleted anti-inflammatory butyrate producers (Faecalibacterium, Coprococcus, Butyricicoccus).

74/100

Wastyk

, Gut-microbiota-targeted diets modulate human immune status

Cell · 2021

A high-fermented-food diet significantly increased microbiota diversity (p=0.0023 for observed ASVs) and decreased 19 of 93 measured inflammatory proteins including IL-6. The high-fibre diet comparison arm did not increase cohort-wide microbiota diversity and showed no equivalent reduction in inflammatory markers, a null result that challenges the assumption that fibre alone improves microbial ecology.[5]

72/100

04Stakes

The Downstream Costs of Gut-Brain Disruption

When microbial ecology deteriorates (through poor diet, chronic stress, or antibiotic disruption), the consequences cascade across mood, cognition, immunity, and metabolic function.

01 System 01 · System 01

Mood & Emotional Regulation

Depression affects approximately 280 million people globally, with up to 35% experiencing treatment-resistant depression to conventional pharmacotherapy.[18] The gut microbiome represents a plausible upstream contributor: Gao et al.'s meta-analysis of 4,883 participants found a consistent pro-inflammatory, butyrate-depleted microbial signature in depressive disorder.[4] The causal direction is not yet established in human trials, but the bidirectional feedback between dysbiosis and depressive symptoms creates a self-reinforcing cycle that conventional antidepressants do not address.[21][33]

280

In practice

persistent low mood, emotional flatness, reduced motivation, anhedonia

02 System 02 · System 02

Cognitive Performance

A 2023 meta-analysis of antibiotic-induced dysbiosis in animal models found that 62.5% of test populations showed decreased spatial cognition following microbiome disruption, with depression-like behaviour increases in 40.7% of populations.[15] In humans, a pooled meta-analysis found a statistically significant negative association between antibiotic use and cognitive outcomes (effect: −0.11, 95% CI: −0.15 to −0.07).[15] These findings suggest that microbiome disruption has measurable cognitive costs, though the animal-to-human extrapolation requires caution.

2023

In practice

brain fog, difficulty concentrating, reduced working memory, mental fatigue

System 03 · System 03

Stress Response & HPA Axis

Chronic stress elevates cortisol, which increases intestinal permeability, which allows bacterial lipopolysaccharides to enter the bloodstream, which triggers neuroinflammation, which sustains the stress response, a vicious cycle documented in both animal and human research.[32][10] The gut-brain stress loop means that stress does not merely affect digestion; it remodels the microbial ecosystem in ways that perpetuate the stress itself. The Bosch et al. (2022) multi-ethnic study of 3,211 participants found gut alpha diversity independently predicted depressive symptoms across six ethnic groups.[6]

In practice

heightened anxiety, poor stress recovery, irritability, disrupted sleep onset

04 System 04 · System 04

Immune & Inflammatory Status

Dysbiosis increases pro-inflammatory cytokines systemically, a state linked to the concept of neuroinflammation, where peripheral immune activation crosses the blood-brain barrier to affect microglial activity.[19][24] The economic burden of anxiety and depression attributable to these interconnected pathways reaches approximately $1 trillion annually in lost productivity and healthcare costs.[18] Immune disruption from the gut does not stay in the gut; it reaches the brain through well-characterised molecular pathways.

In practice

frequent illness, slow recovery, chronic low-grade fatigue, joint stiffness

05Protocol

A 4-Step Gut-Brain Signal Protocol

These four interventions are grounded in the strongest available evidence. They are not a cure for depression or a substitute for clinical care. They are a signal-engineering approach to improving the quality of the messages your gut sends to your brain.

The protocol, as a sequence.

Daily → Daily → Targeted → Ongoing

01 Step 01 · Daily

Fermented Food Diversity

Consume 4–6 servings of fermented foods daily, yoghurt, kefir, kimchi, sauerkraut, kombucha, miso, prioritising variety over volume.

Why

The Wastyk et al. Cell trial found that a high-fermented-food diet increased microbiota diversity (p=0.0023) and decreased 19 inflammatory proteins over ten weeks, while a high-fibre diet did not produce the same immune benefit.[5] Diversity of fermented sources matters because different foods introduce different microbial species.

4–6 Consume 4–6 servings of fermented foods daily, yoghurt, kefir, kimchi, sauerkrau

Common mistake

Eating the same yoghurt every day. Diversity of fermented sources introduces new species; repetition feeds existing ones without expanding the community.

02 Step 02 · Daily

Prebiotic Fibre as Substrate

Maintain 25–35g of dietary fibre daily from diverse plant sources, legumes, alliums, whole grains, vegetables, as metabolic substrate for existing microbiota.

Why

Fibre is fermented into SCFAs by colonic bacteria. Berding et al.'s psychobiotic diet trial showed a 32% decrease in perceived stress (vs. 17% control) with a diet emphasising both prebiotic fibre and fermented foods.[12] The Freijy "Gut Feelings" RCT found prebiotic-rich diets improved mood disturbance (Cohen's d = −0.60, P=0.039).[13]

25–35 Maintain 25–35g of dietary fibre daily from diverse plant sources, legumes, alli

Common mistake

Assuming fibre supplements equal dietary fibre. Whole-food fibre provides the structural diversity that microbes need; isolated supplements (e.g., inulin powder) may not replicate the full prebiotic effect.

03 Step 03 · Targeted

Strain-Specific Psychobiotics

If supplementing, select evidence-backed strains, B. longum 1714, L. helveticus R0052, B. longum R0175, based on published RCT evidence rather than marketing claims.

Why

Allen et al. demonstrated that B. longum 1714 reduced cortisol, stress, and cognitive errors in a crossover RCT (Cohen's d=0.53).[3] The effect was strain-specific, not all probiotics produce psychobiotic effects, and blanket probiotic claims are not supported by the meta-analytic evidence.[17][2]

1714 If supplementing, select evidence-backed strains, B. longum 1714, L. helveticus

Common mistake

Buying generic "probiotic" supplements without checking strain identity. The effect is strain-specific; a product listing only genus and species (e.g., "Lactobacillus acidophilus") without strain designation provides no evidence of psychobiotic benefit.

04 Step 04 · Ongoing

Stress-Microbiome Interruption

Actively manage chronic stress to prevent the cortisol-dysbiosis-inflammation feedback loop from degrading microbial ecology.

Why

Leigh et al. documented that chronic stress increases intestinal permeability, alters microbial composition, and sustains the HPA axis dysregulation that initiated the cycle.[32] Sudo's foundational work showed that microbial colonisation calibrates the stress response, meaning stress management is itself a microbiome intervention.[27]

Actively manage chronic stress to prevent the cortisol-dysbiosis-inflammation fe

Common mistake

Treating gut health and stress management as separate projects. The gut-brain axis means they are bidirectionally coupled, chronic unmanaged stress undermines dietary interventions by degrading the microbial ecosystem they are designed to support.

06Verdict

The verdict.

"The gut is not following the brain's orders. It is sending signals the brain cannot afford to ignore." John F. Cryan, Professor of Anatomy & Neuroscience, University College Cork

Bottom line

The gut-brain axis is not optional biology. It is the upstream input that most performance strategies have been built without. Correcting that omission may be the most consequential thing you do for your brain this year.

The evidence across 42 peer-reviewed sources and five flagship studies converges on a single reframing: the bacterial ecology in your gut is not a passive bystander to your mental life. It manufactures neurotransmitter precursors, calibrates your stress axis, modulates your immune system, and sends continuous signals to your brain through the longest cranial nerve in your body. The causal directio

The whole argument, on one axis

Diet changes stress. Specifically.

01Claim

The Microbiome Modulates Brain Function

The gut microbiome influences mood, stress, and cognition through four converging pathways (neural, metabolic, endocrine, and immune), with effects replicated across independent cohorts and confirmed by interventional trials. The evidence is strongest for the microbiome-depression association and for strain-specific probiotic effects on mood.

02Consequence

Ignoring the Gut Means Ignoring a Major Brain Input

People who troubleshoot cognitive performance, emotional regulation, or stress tolerance without considering the gut-brain axis are missing a significant upstream variable. The cost is not catastrophic for everyone. But for those with chronic low mood, unexplained cognitive fog, or treatment-resistant stress, the microbiome may be the unaddressed factor.

03Lever

Diet and Strain-Specific Supplementation Are the Actionable Levers

The evidence supports fermented food diversity, prebiotic fibre intake, and targeted psychobiotic strains as the three dietary levers with the strongest gut-brain evidence, combined with stress management to prevent the cortisol-dysbiosis feedback loop from undermining microbial interventions.

07Bibliography

42 sources · ~6h est. corpus read · 42 visible

Meta · 6 Review · 1 Journal · 35

Type

Sort

01 Journal

Radjabzadeh, D., Bosch, J. A., Uitterlinden, A. G., Zwinderman, A. H., Ikram, M. A., van Meurs, J. B. J., Luik, A. I., Nieuwdorp, M., Lok, A., van Duijn, C. M., Kraaij, R., & Amin, N2022

Gut microbiome-wide association study of depressive symptoms

Nature Communications1467-022
02 Meta

Asad, A., Kirk, M., Zhu, S., Dong, X., & Gao, M2024

Effects of prebiotics and probiotics on symptoms of depression and anxiety in clinically diagnosed samples: Systematic review and meta-analysis of randomized controlled trials

Nutrition Reviews
03 Journal

Allen, A. P., Hutch, W., Borre, Y. E., Kennedy, P. J., Temko, A., Boylan, G., Murphy, E., Cryan, J. F., Dinan, T. G., & Clarke, G2016

Bifidobacterium longum 1714 as a translational psychobiotic: Modulation of stress, electrophysiology and neurocognition in healthy volunteers

Translational Psychiatry6(11)
04 Meta

Gao, M., Wang, J., Liu, P., Tu, H., Zhang, R., Zhang, Y., Sun, N., & Zhang, K2023

Gut microbiota composition in depressive disorder: A systematic review, meta-analysis, and meta-regression

Translational Psychiatry1398-023
05 Journal

Wastyk, H. C., Fragiadakis, G. K., Perelman, D., Dahl, W. J., Sonnenburg, J. L., & Gardner, C. D2021

Gut-microbiota-targeted diets modulate human immune status

Cell184(16) · 4137–4153
06 Journal

Bosch, J. A., Nieuwdorp, M., Zwinderman, A. H., Deschasaux, M., Radjabzadeh, D., Kraaij, R., Davids, M., de Rooij, S. R., & Lok, A2022

The gut microbiota and depressive symptoms across ethnic groups

Nature Communications1467-022
07 Journal

Han, Y., Wang, B., Gao, H., He, C., Hua, R., Liang, C., Zhang, S., Wang, Y., Xin, S., & Xu, J2022

Vagus nerve and underlying impact on the gut microbiota-brain axis in behavior and neurodegenerative diseases

Journal of Inflammation Research6213–6230
08 Journal

Chen, Y., Xu, J., & Chen, Y2021

Regulation of neurotransmitters by the gut microbiota and effects on cognition in neurological disorders

Nutrients13(6)
09 Journal

Silva, Y. P., Bernardi, A., & Frozza, R. L2020

The role of short-chain fatty acids from gut microbiota in gut-brain communication

Frontiers in Endocrinology
10 Journal

Rusch, J. A., Layden, B. T., & Dugas, L. R2023

Signalling cognition: The gut microbiota and hypothalamic-pituitary-adrenal axis

Frontiers in Endocrinology
11 Journal

Ahmed, H., Leyrolle, Q., Koistinen, V., Kärkkäinen, O., Layé, S., Delzenne, N., & Hanhineva, K2022

Microbiota-derived metabolites as drivers of gut–brain communication

Gut Microbes14(1)
12 Journal

Berding, K., Bastiaanssen, T. F. S., Moloney, G. M., Boscaini, S., Strain, C. R., Anesi, A., Long-Smith, C., Mattivi, F., Stanton, C., Clarke, G., Dinan, T. G., & Cryan, J. F2022

Feed your microbes to deal with stress: A psychobiotic diet impacts microbial stability and perceived stress in a healthy adult population

Molecular Psychiatry1380-022
13 Journal

Freijy, T. M., Cribb, L., Oliver, G., Metri, N. J., Opie, R. S., Jacka, F. N., Hawrelak, J. A., Rucklidge, J. J., Ng, C. H., & Sarris, J2023

Effects of a high-prebiotic diet versus probiotic supplements versus synbiotics on adult mental health: The "Gut Feelings" randomised controlled trial

Frontiers in Neuroscience
14 Journal

Wang, H., Braun, C., Murphy, E. F., & Enck, P2019

Bifidobacterium longum 1714™ strain modulates brain activity of healthy volunteers during social stress

American Journal of Gastroenterology
15 Meta

Hayer, S. S., Hwang, S., & Clayton, J. B2023

Antibiotic-induced gut dysbiosis and cognitive, emotional, and behavioral changes in rodents: A systematic review and meta-analysis

Frontiers in Neuroscience
16 Meta

Cooke, M. B., Catchlove, S., & Tooley, K. L2022

Examining the influence of the human gut microbiota on cognition and stress: A systematic review of the literature

Nutrients14(21)
17 Meta

Cruz Mosquera, F. E., Lizcano Martinez, S., & Liscano, Y2024

Effectiveness of psychobiotics in the treatment of psychiatric and cognitive disorders: A systematic review of randomized clinical trials

Nutrients16(9)
18 Journal

Kumar, A., Pramanik, J., Goyal, N., Chauhan, D., Sivamaruthi, B. S., Prajapati, B. G., & Chaiyasut, C2023

Gut microbiota in anxiety and depression: Unveiling the relationships and management options

Pharmaceuticals16(4)
19 Journal

Tan, H2023

The microbiota-gut-brain axis in stress and depression

Frontiers in Neuroscience
20 Journal

Lewandowska-Pietruszka, Z., Figlerowicz, M., & Mazur-Melewska, K2022

The history of the intestinal microbiota and the gut-brain axis

Pathogens11(12)
21 Journal

Denman, C. R., Park, S. M., & Jo, J2023

Gut-brain axis: Gut dysbiosis and psychiatric disorders in Alzheimer's and Parkinson's disease

Frontiers in Neuroscience
22 Journal

Berding, K., Vlckova, K., Marx, W., Schellekens, H., Stanton, C., Clarke, G., Jacka, F., Dinan, T. G., & Cryan, J. F2021

Diet and the microbiota–gut–brain axis: Sowing the seeds of good mental health

Advances in Nutrition12(4) · 1455–1492
23 Journal

Cryan, J. F., O'Riordan, K. J., Cowan, C. S. M., Sandhu, K. V., Bastiaanssen, T. F. S., Boehme, M., Codagnone, M. G., Cussotto, S., Fulling, C., Golubeva, A. V., Guzzetta, K. E., Jaggar, M., Long-Smith, C. M., Lyte, J. M., Martin, J. A., Molinero-Perez, A., Moloney, G., Morelli, E., Morillas, E., … Dinan, T. G2019

The microbiota-gut-brain axis

Physiological Reviews99(4) · 1877–2013
24 Journal

Mayer, E. A., Tillisch, K., & Gupta, A2015

Gut/brain axis and the microbiota

Journal of Clinical Investigation125(3) · 926–938
25 Journal

Strandwitz, P2018

Neurotransmitter modulation by the gut microbiota

Brain Research128–133
26 Journal

Lach, G., Schellekens, H., Dinan, T. G., & Cryan, J. F2018

Anxiety, depression, and the microbiome: A role for gut peptides

Neurotherapeutics15(1) · 36–59
27 Journal

Sudo, N., Chida, Y., Aiba, Y., Sonoda, J., Oyama, N., Yu, X.-N., Kubo, C., & Koga, Y2004

Postnatal microbial colonization programs the hypothalamic-pituitary-adrenal system for stress response in mice

Journal of Physiology558(1) · 263–275
28 Journal

Dinan, T. G., Stanton, C., & Cryan, J. F2013

Psychobiotics: A novel class of psychotropic

Biological Psychiatry74(10) · 720–726
29 Review

Mayer, E. A., Nance, K., & Chen, S2021

The gut-brain axis

Annual Review of Medicine73(1) · 439–453
30 Journal

Appleton, J2018

The gut-brain axis: Influence of microbiota on mood and mental health

Integrative Medicine: A Clinician's Journal17(4) · 28–32
31 Journal

Michel, K., Rühl, A., Hunne, B., Ponzetto, C., & Furness, J. B2022

How big is the little brain in the gut? Neuronal numbers in the enteric nervous system of mice, guinea pig, and human

Neurogastroenterology & Motility34(12)
32 Journal

Leigh, S. J., Morris, M. J., & Beilharz, J. E2023

The impact of acute and chronic stress on gastrointestinal physiology and function: A microbiota–gut–brain axis perspective

Journal of Physiology601(20) · 4491–4516
33 Meta

Cheung, S. G., Goldenthal, A. R., Uhlemann, A.-C., Mann, J. J., Miller, J. M., & Sublette, M. E2019

Systematic review of gut microbiota and major depression

Frontiers in Psychiatry
34 Journal

Sender, R., Fuchs, S., & Milo, R2016

Revised estimates for the number of human and bacteria cells in the body

Cell164(3) · 337–340
35 Journal

Yano, J. M., Yu, K., Donaldson, G. P., Shastri, G. G., Ann, P., Ma, L., Nagler, C. R., Ismagilov, R. F., Mazmanian, S. K., & Hsiao, E. Y2015

Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis

Cell161(2) · 264–276
36 Journal

Bravo, J. A., Forsythe, P., Chew, M. V. M., Escaravage, E., Savignac, H. M., Dinan, T. G., Bienenstock, J., & Cryan, J. F2011

Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve

Proceedings of the National Academy of Sciences108(38) · 6050–1605
37 Journal

Sudo, N2019

Biogenic amines, gut microbiota, and the gut–brain axis

Advances in Experimental Medicine and Biology25–35
38 Journal

Holzer, P., & Farzi, A2014

Neuropeptides and the microbiota-gut-brain axis

Advances in Experimental Medicine and Biology195–219
39 Journal

Clarke, G., Grenham, S., Scully, P., Fitzgerald, P., Moloney, R. D., Shanahan, F., Dinan, T. G., & Cryan, J. F2013

The microbiome-gut-brain axis during early life regulates the hippocampal serotonergic system in a sex-dependent manner

Molecular Psychiatry18(6) · 666–673
40 Journal

Selber-Hnatiw, S., Rukundo, B., Ahmadi, M., Bahr, H., Basiliko, N., & Bhatt, V2017

Human gut microbiota: Toward an ecology of disease

Frontiers in Microbiology
41 Journal

Cani, P. D2018

Human gut microbiome: Hopes, threats and promises

Gut67(9) · 1716–1725
42 Journal

Carabotti, M., Scirocco, A., Maselli, M. A., & Severi, C2015

The gut-brain axis: Interactions between enteric microbiota, central and enteric nervous systems

Annals of Gastroenterology28(2) · 203–209

The Gut-Brain Axis: What the Science Actually Shows About Your Microbiome, Mood, and Focus.

500 million enteric neurons were never in the textbooks

The Signalling Architecture Behind Gut-Brain Communication