Field Guide
Irritable Bowel Syndrome (IBS)
A disorder of gut-brain communication where the intestine is structurally normal but functionally hypersensitive — driving pain, altered bowel habits, and unpredictable flares. Functional medicine looks upstream at SIBO, dysbiosis, food triggers, nervous-system tone, and unresolved stress.
Think of IBS as a hyper-sensitive smoke detector in your gut. The kitchen isn't on fire — the alarm is just set to trigger at the slightest whiff of toast.
In plain English
Irritable Bowel Syndrome (IBS) is a disorder of gut-brain communication. Standard imaging and scopes come back normal, but the intestine is functionally hypersensitive — normal stretch, normal gas, and normal peristalsis register as pain and urgency.
It's not one disease. Roughly a third of cases are driven by SIBO (small intestinal bacterial overgrowth), another third by post-infectious changes after food poisoning (anti-vinculin antibodies), and the rest by dysbiosis, food reactivity, and nervous-system dysregulation — usually a mix.
The IBS-D (diarrhea-predominant), IBS-C (constipation-predominant), and IBS-M (mixed) subtypes each point to different upstream drivers. Effective functional care identifies which pattern you have, tests for the actual driver, and treats it — rather than just managing symptoms with fiber and antispasmodics.
Where you feel it
The step-by-step
- 1Initial insult
Food poisoning, chronic stress, antibiotic course, or gut infection disrupts the microbiome.
- 2Nerve and microbe changes
SIBO, dysbiosis, or anti-vinculin antibodies develop; motility patterns shift.
- 3Visceral hypersensitivity
The gut-brain axis amplifies normal signals into pain, urgency, and bloating.
- 4Stress-symptom loop
Stress worsens symptoms; symptoms worsen stress. The loop self-reinforces.
Symptoms, causes & labs
- Abdominal pain or cramping relieved (or worsened) by bowel movements
- Alternating constipation and diarrhea (IBS-M) or one dominant pattern (IBS-C, IBS-D)
- Bloating and visible distension worsening through the day
- Urgency, mucus in stool, or incomplete evacuation
- Symptoms clearly flare with stress or specific foods
- SIBO (small intestinal bacterial overgrowth) — present in a large minority of IBS cases
- Post-infectious IBS after food poisoning (anti-vinculin antibodies)
- Dysbiosis, low stomach acid, poor bile flow
- Visceral hypersensitivity driven by nervous-system dysregulation
- FODMAP / histamine / gluten reactivity
- SIBO breath test (lactulose or glucose)
- Comprehensive stool analysis (GI-MAP)
- IBS-Smart antibodies (anti-CdtB, anti-vinculin) for post-infectious IBS
- Elimination diet (low-FODMAP, low-histamine) with practitioner guidance
Red flags — don't wait
- Blood in stool, black tarry stool, or unexplained weight loss
- New IBS-like symptoms starting after age 50
- Nighttime diarrhea that wakes you from sleep, fever, or family history of colon cancer or IBD
Supportive habits to discuss
- Ask for a SIBO breath test and IBS-Smart antibody panel before assuming it's 'just IBS'
- Trial a low-FODMAP diet for 4–6 weeks with a practitioner, then systematically re-introduce
- Address the nervous system — gut-directed hypnotherapy has stronger evidence than most medications for IBS
Is this pattern showing up in your body?
Take our physician-designed assessment — 7 minutes, 70 questions across 20 root-cause categories.
Related categories
Medical disclaimer
This page is educational only. It is NOT medical advice, diagnosis, or treatment. Do not self-treat based on the information here. If you have symptoms, consult a licensed healthcare professional.