Case Study: Severe Bloating and Anxiety in a 29-Year-Old Woman — SIBO Eradication and Gut-Brain Axis Restoration Using the Functional Health Matrix

Illustrative composite — not a single patient. This case study is a teaching composite synthesised from anonymised patterns in the published clinical literature and Nutri-Link case-history references. It does not describe a specific identifiable patient seen by Codenutri Ltd or any single practitioner. Names, demographic specifics, and quoted dialogue are constructed for educational illustration. Always work with a registered clinician for individual care. Editorial review by Chris Massamba, Dip CNM, FMCHC.

Key learning points

• Severe bloating and anxiety are frequently two expressions of the same underlying pathophysiology: small intestinal bacterial overgrowth disrupting the bidirectional gut-brain axis through microbial metabolite signalling, low-grade immune activation, and vagal afferent dysfunction.
• Herbal antimicrobial therapy (oregano oil and berberine) achieves SIBO eradication rates equivalent to rifaximin in appropriately selected patients; breath test confirmation at week 6 provides objective evidence of treatment response.
• Vagal tone restoration — through structured breathwork, humming, cold water facial immersion, and diaphragmatic retraining — breaks the gut-brain feedback loop that perpetuates both gastrointestinal and neuropsychiatric symptoms.
• Patients who have been told their symptoms are "just IBS" or "just anxiety" for years frequently have measurable, treatable pathology when the appropriate functional tests are ordered. Anxiety is not always originating in the mind.
• The low-FODMAP diet is a diagnostic and therapeutic tool for SIBO, not a permanent diet. Structured reintroduction is essential to prevent nutritional restriction and microbiome narrowing.
• Outcomes are illustrative and reflect composite patterns. Individual responses vary depending on SIBO type, duration, root cause, and adherence.

Patient Presentation

Emma (not her real name), a 29-year-old marketing manager from Bristol, presented to the clinic in March 2026 after three years of progressively worsening gastrointestinal and neuropsychiatric symptoms that had begun to threaten her career and relationships.

Her presenting complaint, in her own words: "I wake up with a flat stomach and by 10 am I look six months pregnant. The bloating is so severe some days I can't button my trousers. I've had to leave meetings because of the pain and the noise my stomach makes. But honestly, the worst part isn't even the bloating — it's the anxiety. I've always been a bit of a worrier, but in the last two years it's become something else entirely. I have panic attacks now. Racing heart, can't breathe, convinced I'm dying. My GP prescribed sertraline. It helped a tiny bit with the panic but made the bloating so much worse I had to stop. Then she said it was probably IBS and anxiety feeding each other. I was given a leaflet on the low-FODMAP diet and sent on my way. No one tested anything. No one connected the dots."

Emma's symptom timeline revealed a distinct trigger event. In late 2022, she had contracted a severe bout of gastroenteritis whilst travelling in Southeast Asia — vomiting, diarrhoea, and fever lasting ten days. Within weeks of returning to the UK, she developed new-onset bloating that worsened progressively after meals, erratic bowel habits oscillating between constipation and loose stools, and an unfamiliar and intrusive level of anxiety that felt qualitatively different from her baseline tendency to worry. She described the anxiety as "physical — it starts in my stomach and rises up into my chest, not the other way around."

She had consulted three GPs and one gastroenterologist over three years. She had been diagnosed with IBS, prescribed mebeverine (no benefit), simethicone (minimal benefit), sertraline (discontinued due to gastrointestinal side effects), and propranolol for situational anxiety (partial benefit). She had tried the low-FODMAP diet independently for three weeks — "I felt maybe 40% better but I couldn't sustain it without proper guidance and I didn't know when to reintroduce." She was taking omeprazole 20 mg daily for reflux (self-initiated, not prescribed) and drank 3-4 cups of coffee daily to manage the fatigue that accompanied her symptoms.

Initial Clinical Assessment

Using a structured nutritional deficiency review — informed by the Stewart Nutrition practitioner reference (Stewart, 2024) and aligned with NICE Clinical Knowledge Summaries and NIH Office of Dietary Supplements guidance — the practitioner systematically assessed Emma for nutritional insufficiencies that could be contributing to her clinical picture:

Gastrointestinal system: Severe postprandial bloating (onset within 30-60 minutes of eating, peaking at 2-3 hours), visible abdominal distension described as "six months pregnant," erratic bowel habits (constipation alternating with urgent loose stools), excessive flatulence, and reflux despite omeprazole use. Food triggers reported: onions, garlic, apples, bread, pasta, beans, and most cruciferous vegetables — a pattern classic for fermentable oligosaccharide, disaccharide, monosaccharide and polyol (FODMAP) intolerance secondary to small intestinal bacterial overgrowth (Pimentel and Lembo, 2020).

Nervous system: Generalised anxiety (scoring 18/21 on GAD-7), panic attacks (2-3 per week), brain fog described as "my thoughts feel wrapped in cotton wool," poor concentration and word-finding difficulty, restless sleep with early morning waking — pattern suggestive of neurotransmitter disruption via the microbiota-gut-brain axis (Cryan et al., 2019), possible magnesium and B-vitamin insufficiencies, and vagal afferent dysfunction (Breit et al., 2018).

Energy systems: Fatigue that worsened as the day progressed, postprandial somnolence, carbohydrate cravings, and cold extremities — consistent with mitochondrial energy compromise secondary to chronic low-grade inflammation, possible iron insufficiency, and blood sugar dysregulation driven by erratic eating patterns (Stewart, 2024).

Immune system: Frequent upper respiratory infections (3-4 per year), slow recovery from minor illness, history of severe gastroenteritis as the likely initiating trigger — suggesting post-infectious disruption of the gut microbiome and mucosal immune function (Pimentel and Lembo, 2020).

Musculoskeletal system: Muscle twitching (particularly eyelid and calf), occasional nocturnal leg cramps, tension headaches (2-3 per week) — suggestive of magnesium insufficiency (Stewart, 2024).

Skin and mucous membranes: Dry skin, cracked lip corners (angular cheilitis), brittle nails with ridging — signs of essential fatty acid deficiency, iron insufficiency, and possible B-vitamin depletion.

Psychological status: Clinically significant anxiety with panic features; hypervigilance to bodily sensations (interoceptive sensitivity); catastrophic interpretation of gastrointestinal symptoms ("when my stomach bloats I become convinced something is seriously wrong"); avoidance behaviours including reducing social engagements and calling in sick to work — consistent with the gut-brain axis literature demonstrating bidirectional amplification between visceral hypersensitivity and anxiety (Cryan et al., 2019; Berentsen et al., 2022).

The pattern was clear: this was not two separate conditions — IBS and anxiety — running in parallel. This was a single, integrated disorder of the gut-brain axis, initiated by infectious gastroenteritis, perpetuated by SIBO-driven bacterial fermentation and low-grade immune activation, and amplified by vagal afferent dysfunction that simultaneously worsened gut motility and signalled threat to the brain (Pimentel and Lembo, 2020; Breit et al., 2018). The sertraline had exacerbated the gastrointestinal component by further altering gut motility and the microbiome — a phenomenon well-recognised in the literature (Bested, Logan and Selhub, 2013).

From the literature: "The microbiota-gut-brain axis is a bidirectional communication system that enables gut microbes to communicate with the brain and the brain to communicate with the gut. This communication occurs via neural, endocrine, and immune pathways and is fundamental to maintaining homeostasis." — Cryan et al., Physiological Reviews 2019

Legend: This is an illustrative composite, not a single patient. Demographics and details are constructed for educational illustration.

Interpretation: A 29-year-old woman with a classic post-infectious SIBO presentation where the gastrointestinal and neuropsychiatric symptoms are two expressions of the same gut-brain axis dysfunction. Three years of symptom escalation without definitive testing meant the root cause — hydrogen-dominant SIBO — had never been identified. The patient's own observation that "the anxiety starts in my stomach and rises up" was a precise lay description of vagal afferent signalling driving interoceptive threat perception.

Clinical pearl: When a young woman with "IBS and anxiety" reports that her anxiety feels qualitatively different from ordinary worry — "physical," "rising from the stomach" — and dates its onset to a gastrointestinal infection, the appropriate clinical response is to test for SIBO, assess intestinal permeability, and evaluate the gut-brain axis, not to add a second psychiatric medication. Post-infectious SIBO is a treatable driver of both gastrointestinal and neuropsychiatric symptoms.

Functional Health Matrix Assessment

Emma was scored across all seven nodes of the Functional Health Matrix, with 1 representing severe dysfunction and 5 representing optimal function:

Total Initial Matrix Score: 13/35 — a system with two critically impaired nodes (Assimilation and Communication) driving each other in a pathological feedback loop, with secondary compromise across Energy, Biotransformation, Transport, and Defence.

Legend: Each node scored 1-5 (1 = severely compromised, 5 = optimal). Total out of 35. Clinical rationale documents the evidence for each score. The two nodes scoring 1/5 represent a coupled dysfunction: the gut was driving the brain, and the brain was driving the gut.

Interpretation: The FHM reveals a classic gut-brain axis collapse. Assimilation (1/5) and Communication (1/5) are the two critically affected nodes, and they are causally linked. Post-infectious SIBO is generating bacterial metabolites, activating mucosal immunity, and sending afferent vagal signals that the brain interprets as threat — producing anxiety and panic. The anxiety, in turn, activates sympathetic output that reduces gut motility, worsens SIBO, and increases visceral hypersensitivity. This is a self-reinforcing loop. Therapeutic strategy must simultaneously address both nodes: eradicate SIBO (Assimilation) AND restore vagal tone (Communication).

Figure: Functional Health Matrix — baseline assessment

Description: Radar chart showing 7 nodes with baseline scores. Assimilation (1/5) and Communication (1/5) highlighted in red as primary, coupled therapeutic targets. Defence & Repair (2/5), Energy Production (2/5), Biotransformation & Elimination (2/5), and Transport (2/5) in amber as secondary targets. Structural Integrity (3/5) in pale green. The chart shows the characteristic "gut-brain pincer" pattern where the two lowest nodes are physiologically coupled.

Legend: Each node scored 1-5 (1 = severely compromised, 5 = optimal). Total out of 35. Nodes scoring 1-2 are primary therapeutic targets. The visual shows the gut-brain interconnected pattern where Assimilation and Communication are simultaneously collapsed.

Interpretation: The radar chart shows the gut-brain axis as a unified structure — not two separate problems. Assimilation (SIBO, fermentation, malabsorption) was directly fuelling Communication dysfunction (anxiety, panic, vagal disruption) through bacterial metabolites, immune signalling, and vagal afferent traffic. Any treatment strategy that addressed only the gut (antimicrobials) or only the brain (anxiolytics) would fail because the loop would remain intact. Both nodes required simultaneous intervention.

Wheel of Life Assessment

Total Initial Wheel of Life Score: 25/80 — severe imbalance with Stress Management and Spiritual Practice at crisis level (both 1/10), Movement near crisis (2/10), and Nutrition and Sleep significantly impaired (both 3/10).

Legend: Each dimension scored 1-10. Total out of 80. Lower scores indicate areas of significant lifestyle imbalance requiring attention alongside clinical interventions.

Interpretation: The Wheel reveals a life substantially contracted by the gut-brain axis disorder. The most striking finding is Stress Management at 1/10 — not merely an absence of stress-reduction techniques, but a state of active threat physiology where every gastrointestinal sensation triggered catastrophic interpretation and sympathetic activation. Movement (2/10) had been abandoned due to symptom unpredictability. The absence of any contemplative practice (Spiritual Practice 1/10) meant Emma had no physiological access to the parasympathetic state required for gut healing. These two collapsed dimensions — Stress Management and Spiritual Practice — would require re-framing as physiological interventions, not lifestyle preferences.

Figure: Wheel of Life — baseline assessment

Description: Radar chart showing 8 dimensions with baseline scores. Stress Management (1/10) and Spiritual Practice (1/10) highlighted in red as crisis dimensions. Movement (2/10) in deep amber-red. Nutrition (3/10) and Sleep (3/10) in amber. Relationships (4/10) and Purpose (5/10) in pale amber. Environment (6/10) in pale green.

Legend: Each dimension scored 1-10. Total out of 80. Lower scores indicate areas of significant lifestyle imbalance requiring attention alongside clinical interventions.

Interpretation: The Wheel was severely collapsed on the psychological and physical health axes. The compound effect of no stress-management practice (1/10), no contemplative/parasympathetic practice (1/10), abandoned movement (2/10), and a fear-driven diet (3/10) created a physiological environment in which the gut could not heal and the brain could not down-regulate threat perception. Pharmacological or antimicrobial treatment alone could not succeed in this context.

Functional Testing Ordered

Based on the clinical presentation and matrix assessment, the following functional tests were ordered. For broader context on functional medicine testing rationale, see the companion reference article.

SIBO Lactulose Breath Test (3-hour):

• Hydrogen-positive SIBO: baseline hydrogen 14 ppm, peak rise to 92 ppm at 90 minutes (positive threshold: rise of >20 ppm above baseline within 90 minutes)
• Methane: negative throughout (peak 6 ppm)
• Pattern consistent with hydrogen-dominant small intestinal bacterial overgrowth affecting the proximal-to-mid small bowel
• Symptom correlation: severe bloating reported at 60-120 minutes, corresponding to peak hydrogen production

Comprehensive Stool Analysis (Genova Diagnostics GI Effects):

• Faecal calprotectin: 74 microg/g (mildly elevated, reference <50 — indicating low-grade mucosal inflammation consistent with SIBO)
• Pancreatic elastase: 312 microg/g (normal, reference >200)
• Zonulin: 128 ng/mL (elevated, reference <107 — indicating increased intestinal permeability) (Tajik et al., 2020)
• Short-chain fatty acids: butyrate low at 3.8 micromol/g (reference >6.0), total SCFAs below reference range — consistent with compromised colonic fermentation and the dysbiosis expected with chronic SIBO
• Commensal bacteria: reduced Bifidobacterium and Faecalibacterium prausnitzii, elevated Streptococcus species
• No pathogenic bacteria, ova, or parasites detected

Nutritional Evaluation:

• 25-OH Vitamin D: 32 nmol/L (deficient, optimal >75) — relevant to both immune function and mood regulation (Pineda and McGrath, 2021)
• Red blood cell magnesium: 3.9 mg/dL (low, optimal >5.5) — consistent with muscle twitching, cramps, tension headaches, and anxiety (Stewart, 2024)
• Serum B12: 238 pg/mL (borderline, optimal >500) — consistent with cognitive symptoms and fatigue, potentially compounded by omeprazole-induced hypochlorhydria
• Ferritin: 28 microg/L (low-normal, optimal >50 for premenopausal women) — consistent with fatigue, brittle nails, and possible suboptimal iron status despite normal haemoglobin
• Omega-3 Index: 4.2% (deficient, optimal >8%)
• hs-CRP: 3.2 mg/L (mildly elevated, optimal <1.0) — confirming low-grade systemic inflammation

HPA Axis Assessment (DUTCH Complete):

• Flattened diurnal cortisol rhythm: morning cortisol borderline low, midday and afternoon within range, evening cortisol elevated — pattern consistent with HPA axis dysregulation under chronic stress
• Cortisol awakening response (CAR): 22% rise (blunted, optimal >50%)
• Cortisol-to-DHEA ratio: suggestive of early pregnenolone steal towards cortisol production at the expense of DHEA

Intervention Protocol

The therapeutic strategy followed three phases, addressing the Assimilation and Communication nodes simultaneously — because they were physiologically coupled and could not be treated sequentially. Treating SIBO without restoring vagal tone would leave the motility dysfunction that perpetuates recurrence; treating anxiety without eradicating SIBO would leave the microbial drivers of neuropsychiatric symptoms intact.

Phase 1: Remove and Restore (Weeks 1-4)

Dietary intervention:

• Structured low-FODMAP diet for 4 weeks under practitioner guidance: elimination of all high-FODMAP foods (onion, garlic, wheat, legumes, lactose, apples, pears, stone fruits, cauliflower, mushrooms, honey, artificial polyols) (NICE, 2022)
• Emphasis on easily digestible, nutrient-dense foods: white rice, quinoa, carrots, courgettes, spinach, firm tofu, eggs, chicken, salmon, blueberries, oranges, walnuts, pumpkin seeds, olive oil
• Meal spacing: minimum 3-4 hours between meals to allow the migrating motor complex (MMC) to clear residual bacteria from the small intestine between meals — no snacking
• Elimination of coffee (migrating motor complex disruption), alcohol (gut permeability and mood), and carbonated beverages
• Omeprazole withdrawal over 3 weeks with DGL liquorice and slippery elm for rebound management

For the detailed framework underpinning this approach, see the 5R gut health protocol.

SIBO eradication protocol (herbal antimicrobials):

• Oregano oil (standardised to 70% carvacrol): 200 mg three times daily, weeks 1-4
• Berberine HCl: 500 mg three times daily, weeks 1-4
• Partially hydrolysed guar gum (PHGG): 3 g daily, introduced at week 3 as tolerated (prebiotic to support colonic SCFA production without feeding small intestinal bacteria)

From the literature: "Herbal therapies are at least as effective as rifaximin for resolution of SIBO by lactulose breath testing. Herbals also appear to be as effective as triple antibiotic therapy for SIBO rescue therapy for rifaximin non-responders." — Chedid et al., Global Advances in Health and Medicine 2014

Gut barrier support:

• L-glutamine: 5 g twice daily in water between meals
• Zinc carnosine: 75 mg twice daily
• Vitamin D3: 5,000 IU daily (loading dose for 8 weeks, targeting >75 nmol/L)

Vagal tone restoration programme (initiated week 1, continued throughout):

• Diaphragmatic breathing: 5 minutes, 3× daily — measured by placing one hand on chest and one on abdomen, ensuring abdominal movement without chest movement. This was framed as a physiological vagal stimulation exercise, not a relaxation technique
• Extended exhale breathing (4-second inhale, 8-second exhale): 5 minutes at bedtime — longer exhalation relative to inhalation increases vagal output to the heart and gut (Breit et al., 2018)
• Humming: 2 minutes, 2× daily (vibration of the vocal cords directly stimulates the vagus nerve via its pharyngeal branch)
• Cold water facial immersion: 30 seconds each morning (triggers the mammalian dive reflex, activating the vagus nerve and shifting autonomic balance towards parasympathetic)
• Gargling vigorously with water: 30 seconds, 2× daily — stimulates the pharyngeal branch of the vagus nerve

Phase 2: Repair and Rebalance (Weeks 5-8)

Confirm SIBO eradication:

• Repeat lactulose breath test at week 6: hydrogen peak 16 ppm (negative), confirming eradication of hydrogen-dominant SIBO

FODMAP reintroduction (structured, systematic):

• Week 5-8: systematic reintroduction of individual FODMAP groups — one group per 3-day challenge, monitoring symptom response. Lactose, then excess fructose, then sorbitol, then mannitol, then fructans (garlic/onion), then GOS (legumes)
• Personalised tolerance thresholds established: onion and garlic tolerable in small amounts (fructans), large quantities of apple and pear remain triggers (excess fructose + sorbitol), legumes well-tolerated in moderate portions

Anti-inflammatory and nutrient repletion:

• Omega-3 fatty acids (EPA/DHA): 2,000 mg daily (targeting Omega-3 Index >8%)
• Magnesium glycinate: 400 mg at bedtime (addressing muscle twitching, tension headaches, and supporting GABAergic neurotransmission relevant to anxiety)
• Activated B-complex: 1 capsule daily with breakfast
• Vitamin D3 maintenance: 2,000 IU daily
• Probiotic: Lactobacillus rhamnosus GG + Bifidobacterium longum (strains with evidence for both gut barrier support and anxiolytic effects via vagal signalling; Cryan et al., 2019)

Gut-brain axis interventions:

• Gut-directed hypnotherapy: 20-minute audio programme daily (evidence-based intervention for IBS with significant effect sizes for both gastrointestinal and anxiety symptoms)
• Continued daily vagal tone exercises with progression: diaphragmatic breathing extended to 10 minutes, 2× daily

Phase 3: Integrate and Maintain (Weeks 9-12)

Movement reintroduction:

• Week 9: daily 15-minute walks after largest meal (supports gastric emptying plus vagal tone through rhythmic movement)
• Week 10: reintroduction of gentle yoga (yin style, 20 minutes, 3× weekly — avoiding inversion poses that could trigger reflux)
• Weeks 11-12: return to gym-based resistance training, 2× weekly (pre-bloating identity restoration; exercise is a vagal stimulant through rhythmic breathing)

Sleep optimisation:

• Consistent sleep window: 22:30-06:30
• Magnesium glycinate 400 mg + glycine 3 g at bedtime
• Phone removed from bedroom; replaced with book and amber reading lamp
• No screens after 21:00
• Bedtime routine: warm shower, 8-second exhale breathing, gratitude journal (3 items)

Stress and cognition:

• Morning vagal reset: 30 seconds cold water facial immersion + 2 minutes humming + 5 minutes diaphragmatic breathing (framed as "physiological hygiene," not meditation — which she resisted)
• Cognitive reframing of gut sensations: working with the practitioner, Emma learned to reinterpret gastrointestinal sensations as "gut signals" rather than "threat signals." When she noticed bloating, the practised response became "this is a gut signal, not a danger signal, and I have tools for it" rather than the catastrophic spiral that previously followed
• Reduction of interoceptive hypervigilance through structured exposure: deliberately attending to gut sensations during non-symptomatic periods to decouple the association between "gut sensation" and "imminent panic"

Medication review:

• Propranolol reduced from daily to as-needed situational use
• Omeprazole fully discontinued (gut barrier restored, reflux mechanism addressed through betaine HCl titration with meals during Phase 1)

Practice tip: When presenting a gut-brain axis protocol to a patient who has been told "it's just anxiety" for years, frame the vagal tone exercises as physiological interventions with measurable outputs — not relaxation techniques. Say "we're stimulating a nerve" rather than "try to relax." Patients who have failed at relaxation often succeed at nerve stimulation because it removes the performance pressure and aligns with their experience that the problem is physical.

Safety note: SIBO herbal antimicrobial therapy can produce a die-off reaction (Herxheimer response) — transient worsening of bloating, fatigue, and brain fog — typically days 3-7. Warn patients in advance and distinguish this from treatment failure. Ensure adequate hydration and consider binders (activated charcoal between meals) if the reaction is severe. Always exclude pregnancy before initiating berberine. Monitor liver function if treatment extends beyond 6 weeks.

Medication management (coordinated with her NHS GP):

• Propranolol: transitioned from daily (40 mg) to as-needed situational use (10-20 mg) at week 8
• No other prescription medications in use; sertraline had been discontinued prior to the functional medicine consultation

Figure: Emma — phased intervention timeline

Description: Horizontal timeline showing 3 phases across 12 weeks. Phase 1 (Weeks 1-4): Remove and Restore — structured low-FODMAP diet (onion, garlic, wheat, legumes, lactose, apples, stone fruits, honey eliminated), meal spacing 3-4 hours (no snacking), SIBO eradication (oregano oil 200 mg TID, berberine 500 mg TID weeks 1-4; PHGG from week 3), gut barrier support (L-glutamine, zinc carnosine, vitamin D3 5,000 IU), vagal tone programme (diaphragmatic breathing, extended exhale, humming, cold water facial immersion, gargling daily). Phase 2 (Weeks 5-8): Repair and Rebalance — repeat breath test at week 6 (negative), systematic FODMAP reintroduction (one group per 3-day challenge), omega-3 2,000 mg, magnesium glycinate 400 mg, activated B-complex, vitamin D3 maintenance, probiotics (LGG + B. longum), gut-directed hypnotherapy, continued vagal exercises. Phase 3 (Weeks 9-12): Integrate and Maintain — movement reintroduction (post-meal walks week 9, yoga week 10, gym week 11-12), sleep optimisation (consistent window, magnesium, glycine, no screens), morning vagal reset routine, cognitive reframing of gut sensations, propranolol reduced to as-needed week 8. Re-testing at week 12 marked with triangle.

Legend: Each phase is colour-coded. Overlapping interventions shown as stacked bars. FODMAP reintroduction window highlighted in Phase 2. Breath test confirmation at week 6. The timeline demonstrates the simultaneous gut-brain approach, with vagal tone exercises running continuously from week 1 alongside the antimicrobial protocol.

Interpretation: The 12-week protocol required parallel treatment of the Assimilation and Communication nodes because they were physiologically coupled. Antimicrobial therapy alone, without vagal restoration, would have left the motility dysfunction perpetuating SIBO recurrence. Vagal restoration alone, without SIBO eradication, would have left the microbial drivers of neuropsychiatric symptoms intact. The simultaneous approach — antimicrobials plus vagal tone exercises from day one — addressed the loop at both ends.

Evidence tier summary

Legend: Evidence tiers reflect the strength of the clinical evidence base. "Strong" = systematic reviews or multiple large RCTs. "Moderate" = individual RCTs, well-designed cohort studies, or strong mechanistic data with clinical support. "Emerging" = pilot studies, mechanistic evidence, or expert consensus pending further trials.

Interpretation: The herbal antimicrobial protocol and the gut-brain axis framework both carry strong evidence. The coupling of antimicrobial therapy with vagal tone restoration, whilst mechanistically rational, is an emerging clinical approach without dedicated RCTs. The low-FODMAP diet and selected probiotic strains carry moderate evidence. Vagal tone exercises as a structured therapeutic intervention remain in the emerging evidence category, grounded in mechanistic studies of vagal neuroanatomy and physiology.

Safety note: SIBO herbal antimicrobials can trigger temporary worsening of symptoms (die-off reaction) typically days 3-7 of treatment. Warn patients in advance and distinguish this from treatment failure. Berberine is contraindicated in pregnancy. Severe bloating with alarm features — unintentional weight loss, rectal bleeding, nocturnal symptoms, or family history of colorectal cancer or IBD — requires urgent gastroenterology referral, not functional medicine investigation. Always exclude coeliac disease and IBD before attributing symptoms to SIBO.

Outcomes at 12 Weeks

These outcomes reflect a composite pattern. Individual responses vary depending on SIBO type, duration, underlying root cause, dietary adherence, and consistency with vagal tone exercises. Gut-brain axis disorders respond well to functional medicine but require ongoing maintenance; these results illustrate trajectory, not cure.

Symptom resolution:

• Bloating severity (VAS): reduced from 9/10 to 1/10 — described as "occasional and mild, I can live with it"
• Abdominal distension: resolved; no longer visible or functionally limiting
• Bowel habits: normalised — daily formed stool without urgency or straining
• Anxiety (GAD-7): reduced from 18/21 (severe) to 5/21 (mild) — below clinical threshold
• Panic attacks: from 2-3 per week to zero in weeks 8-12
• Brain fog: resolved — "I didn't realise how much of my cognitive function I'd lost until it came back"
• Fatigue: from 6/10 to 2/10
• Muscle twitching and nocturnal leg cramps: resolved
• Tension headaches: reduced from 2-3× weekly to 1× fortnightly

Repeat functional testing (Week 12):

• SIBO lactulose breath test: negative (peak hydrogen 14 ppm, no rise above baseline >20 ppm)
• Faecal calprotectin: 38 microg/g (normalised, reference <50)
• Zonulin: 82 ng/mL (normalised, reference <107 — gut barrier restored)
• 25-OH Vitamin D: 86 nmol/L (replete)
• RBC magnesium: 5.8 mg/dL (optimal range)
• Serum B12: 486 pg/mL (significant improvement from 238)
• Ferritin: 52 microg/L (optimal, up from 28)
• Omega-3 Index: 7.1% (approaching optimal, up from 4.2%)
• hs-CRP: 0.8 mg/L (normalised from 3.2)
• DUTCH cortisol rhythm: normalised — robust morning rise, appropriate midday and afternoon levels, low evening level

Repeat Functional Health Matrix (Week 12):

Figure: Functional Health Matrix — baseline vs 12-week follow-up

Legend: Score improvement reflects clinical response. The coupled recovery of Assimilation (+3) and Communication (+3) confirms the gut-brain axis as an integrated therapeutic target. Structural Integrity and Transport improved more modestly, reflecting their less impaired baseline scores.

Interpretation: Assimilation and Communication each showed gains of +3, recovering from 1/5 (severely impaired) to 4/5 (near-optimal). This coupled recovery — the two collapsed nodes recovering in parallel — confirms the gut-brain axis as an integrated physiological structure, not two separate systems that happen to affect each other. The residual score of 4/5 in both nodes appropriately reflects that gut-brain axis health requires ongoing maintenance, not a single course of treatment. The total matrix improvement from 13/35 to 27/35 represents a 108% improvement — a system that was collapsing is now functioning near-optimally.

Repeat Wheel of Life (Week 12):

Figure: Wheel of Life — baseline vs 12-week follow-up

Legend: Each dimension scored 1-10. The most dramatic improvements in Stress Management (+6 from crisis level 1/10) and Spiritual Practice (+5 from crisis level 1/10) reflect the reframing of vagal tone exercises as physiological practice, not belief-based meditation.

Interpretation: Stress Management (+6) and Spiritual Practice (+5) showed the greatest gains, reflecting the critical insight that Emma could engage with contemplative practice when it was framed as nerve stimulation rather than spiritual belief. Movement (+5) returned as bloating and urgency resolved. Nutrition (+5) improved through structured FODMAP reintroduction that expanded dietary variety whilst respecting personalised tolerance thresholds. Environment (+1) showed the smallest gain, reflecting the relatively preserved baseline and the limited scope of environmental interventions in this protocol.

Patient testimonial: "Three months ago I was calling in sick to work because I couldn't face a meeting with a stomach that looked pregnant and a brain that felt like it was wrapped in fog. I was having panic attacks in supermarket queues. I thought I was losing my mind. Now — I went for dinner with friends last week. I ate food I hadn't touched in three years. I didn't bloat. I didn't panic. I laughed at a joke and realised halfway through that I wasn't monitoring my stomach. I was just there, in the moment, being a person. That's when I knew I was getting better — when I forgot to scan my body for symptoms. My GP asked what I'd done differently. I said: 'Someone finally tested me for something real. I had SIBO. And then they taught me how to stimulate my vagus nerve.' She looked at me like I'd said something in a foreign language. But my GAD-7 score doesn't lie, and neither does my breath test."

Transferable learning points

1. SIBO is not just a gut condition — it is a gut-brain axis condition. The hydrogen gas, bacterial metabolites, and low-grade immune activation generated by small intestinal bacterial overgrowth do not remain in the gut. They signal to the brain via the vagus nerve, the systemic circulation, and the immune system (Cryan et al., 2019). In a susceptible individual — particularly one with pre-existing anxiety traits or a history of gut infections — this signalling produces genuine neuropsychiatric symptoms that are not "all in the mind" but originate in the small intestine. The chronic fatigue case study demonstrated a similar pattern in the context of post-infectious IBS, and the __LINK_5c06e2ea67e3__ illustrates the broader principle of gut-driven systemic symptoms.

2. Vagal tone is a physiological variable, not a wellness concept. The vagus nerve is the primary conduit of the parasympathetic nervous system to the gut, heart, and lungs. It regulates gut motility (via the migrating motor complex), modulates inflammation (via the cholinergic anti-inflammatory pathway), and transmits afferent signals about the state of the viscera to the brain (Breit et al., 2018). Vagal tone can be measured (via heart rate variability) and it can be trained (via diaphragmatic breathing, cold exposure, humming, and gargling). For a patient whose vagal function has been compromised by chronic stress and gut inflammation, vagal tone restoration is as physiological an intervention as supplementing vitamin D. The 5R gut health protocol provides the structured framework for gut restoration that pairs with vagal tone work.

3. Post-infectious SIBO has a distinct clinical signature. Onset of new gastrointestinal and neuropsychiatric symptoms within weeks of an acute gastroenteritis episode — particularly in a previously healthy young adult — should prompt SIBO breath testing, not an IBS diagnosis and a leaflet. The low-FODMAP diet is a legitimate therapeutic tool, but it does not diagnose or treat the underlying bacterial overgrowth. Breath testing with lactulose provides objective evidence of SIBO and, critically, confirmation of eradication after treatment (Chedid et al., 2014; Pimentel and Lembo, 2020).

4. Patients can engage with contemplative practice when it is framed as physiology. Emma's baseline Spiritual Practice score was 1/10 because she associated meditation and mindfulness with belief systems she did not hold. The reframe — "we are stimulating a nerve, not practising a religion" — made the same practices accessible. The mitochondrial restoration protocol uses a similar physiological framing for interventions that also carry psychological benefits. For practitioners, the lesson is that explaining mechanism ("the vagus nerve responds to extended exhalation") can bypass resistance to practices that are clinically indicated but personally resisted.

When to seek professional support

If you experience persistent bloating with anxiety, panic, brain fog, or fatigue — particularly if symptoms began after a gut infection, a course of antibiotics, or a period of high stress — consider working with a qualified functional medicine practitioner who can test for SIBO and assess the gut-brain axis alongside your conventional medical care.

Functional medicine approaches complement, not replace, conventional gastroenterological and psychiatric management. All medication changes should be coordinated with your prescribing clinician.

If you are experiencing a medical emergency, call 999. For urgent but non-emergency health concerns, contact NHS 111. If you are in emotional distress, contact the Samaritans on 116 123 (free, 24/7) or text SHOUT to 85258.

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If this case study resonated, you may find the following posts clinically relevant:

• The 5R Gut Health Protocol: a functional medicine framework for 2026 — the structured gut restoration framework underpinning Emma's SIBO eradication and barrier repair
• Case Study: Chronic Fatigue, IBS, and Brain Fog — another case where post-infectious gut dysfunction drove multi-system symptoms including cognitive impairment
• Essential Functional Medicine Labs for 2026 — the testing rationale behind SIBO breath tests, zonulin, calprotectin, and comprehensive stool analysis
• Case Study: Long COVID Fatigue and Mitochondrial Restoration — another case where systemic inflammation and gut dysfunction intersected with neuropsychiatric symptoms
• 5R Gut Protocol 2026 Update: microbiome reinoculation and beyond — expanded guidance on the reinoculation phase of gut restoration relevant to post-antimicrobial protocols

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This case study is for educational purposes and represents a composite of clinical patterns seen in practice. Individual patient factors must guide all treatment decisions. Nutritional interventions should be supervised by a qualified functional medicine practitioner.

Practitioner summary

• When a patient presents with concurrent gastrointestinal symptoms (bloating, erratic bowels) and neuropsychiatric symptoms (anxiety, panic, brain fog) that began after an infectious gastroenteritis episode, order a lactulose breath test before labelling the presentation as "IBS plus anxiety" — post-infectious SIBO is a treatable driver of both symptom clusters.
• Herbal antimicrobial therapy (oregano oil 200 mg TID + berberine 500 mg TID for 4 weeks) achieves SIBO eradication equivalent to rifaximin. Confirm eradication with a repeat breath test at week 6.
• Assess gut barrier integrity (serum or faecal zonulin) and order a comprehensive stool analysis in all SIBO patients — intestinal permeability and dysbiosis typically accompany SIBO and require their own therapeutic targets.
• Screen for nutritional deficiencies driven by SIBO-associated malabsorption: vitamin D, magnesium, B12, ferritin, and omega-3 index. The Stewart Nutrition deficiency reference provides a systematic body-system review that will guide targeted testing.
• Prescribe vagal tone restoration exercises alongside antimicrobial therapy — not after. Diaphragmatic breathing, extended exhale breathing, humming, cold water facial immersion, and gargling are physiological vagal stimulants with mechanistic support from the neuroanatomy literature.
• Frame vagal tone exercises as "nerve stimulation" rather than "relaxation techniques" for patients who resist meditation or mindfulness — explain the mechanism and measure the outcome. Present GAD-7 scores as physiological data, not psychological confessions.
• Guide structured FODMAP reintroduction after SIBO eradication — the low-FODMAP diet is a diagnostic and therapeutic tool, not a permanent diet. Systematic reintroduction of individual FODMAP groups prevents nutritional restriction and microbiome narrowing.
• Address meal spacing (minimum 3-4 hours, no snacking) to support the migrating motor complex — the small intestine's endogenous cleaning mechanism that is frequently impaired in SIBO and essential for preventing recurrence.
• Discontinue PPIs with a gradual 3-week taper using DGL liquorice and slippery elm for rebound management; PPI-induced hypochlorhydria impairs protein digestion, mineral absorption, and the gastric acid barrier — each of which perpetuates SIBO risk.
• At follow-up, repeat the Functional Health Matrix to demonstrate the coupled recovery of Assimilation and Communication nodes — this validates the integrated gut-brain axis approach and builds patient confidence in the physiological basis of their improvement.