Irritable Bowel Syndrome (IBS)

Condition: Irritable Bowel Syndrome (IBS)  |  Category: Digestive Health  |  Reviewed by: Brian Lamkin, DO

What Is Irritable Bowel Syndrome?

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by chronic abdominal pain or discomfort associated with altered bowel habits in the absence of structural or biochemical abnormalities detectable by conventional testing. It is one of the most prevalent chronic digestive conditions, affecting an estimated 10 to 15 percent of the global population.

The conventional definition of IBS as a functional disorder has historically implied that no identifiable pathology exists, leaving patients with symptom management as the primary therapeutic goal. Functional medicine challenges this framing. In the majority of IBS cases, identifiable and often treatable upstream drivers exist, including small intestinal bacterial overgrowth (SIBO), intestinal permeability, gut dysbiosis, food sensitivities, histamine intolerance, HPA axis dysfunction, and visceral hypersensitivity driven by prior infection or gut-brain axis dysregulation.

IBS is not a wastebasket diagnosis. It is a final common pathway of multiple distinct, often correctable physiological disruptions that standard gastroenterological evaluation is not designed to identify.

Why It Matters

Common Symptoms

Root Causes: A Functional Medicine Perspective

IBS symptoms are the downstream output of one or more identifiable physiological disruptions. Identifying which driver is dominant in each individual patient determines the most effective treatment approach.

SIBO as the Most Common Identified Driver

SIBO is present in an estimated 50 to 78 percent of IBS patients on breath testing. Bacterial overgrowth in the small intestine ferments carbohydrates that should reach the colon, producing hydrogen and methane gas that causes bloating, pain, and altered motility. Hydrogen-dominant SIBO correlates most strongly with diarrhea-predominant IBS, while methane-dominant SIBO correlates with constipation and bloating that worsens through the day.

Gut Dysbiosis, Intestinal Permeability, and Food Sensitivities

Gut dysbiosis alters the production of short-chain fatty acids, increases intestinal permeability, and impairs immune regulation in the gut-associated lymphoid tissue. Elevated zonulin allows bacterial lipopolysaccharides and partially digested food proteins to cross the epithelial barrier, triggering localized immune activation and visceral hypersensitivity that amplifies pain signaling from normal gut motility. Food sensitivities, distinct from IgE-mediated allergies, involve delayed reactions to specific foods most commonly including gluten, dairy, eggs, corn, soy, and high-FODMAP foods.

HPA Axis Dysfunction and the Gut-Brain Connection

CRH receptors are distributed throughout the gut wall. Psychological and physiological stress activates these receptors directly, increasing intestinal permeability, stimulating mast cell degranulation, and altering mucosal immune activation independently of the systemic HPA response. Cortisol elevation increases intestinal permeability, alters immune tolerance in the gut, and shifts motility patterns in ways that produce or worsen IBS symptoms.

Conventional vs Functional Medicine Approach

Key Labs to Evaluate

A complete IBS evaluation requires testing that identifies the specific drivers rather than confirming the diagnosis by exclusion.

How to Interpret These Labs Together

Common Patterns Seen in Patients

• The patient with a normal colonoscopy told IBS is stress-related: when we run a SIBO breath test, comprehensive stool analysis, and food sensitivity panel, we almost always find at least one and often two or three identifiable, treatable drivers; the stress connection is real but rarely the complete picture
• Post-infectious IBS following a gastrointestinal illness: altered motility and disturbed microbiome persist long after the acute infection resolves; anti-CdtB and anti-vinculin autoantibodies from the prior infection may be sustaining the altered motility and visceral hypersensitivity that produces the ongoing IBS picture
• The constipation-predominant patient with methane-positive SIBO: methanogenic archaea slow transit and produce a symptom picture almost identical to functional constipation; rifaximin plus neomycin or herbal antimicrobials targeting methane producers produces resolution that laxatives cannot achieve
• The woman whose IBS symptoms worsen in the luteal phase: progesterone slows gut motility, and the luteal phase of the menstrual cycle reliably worsens constipation-predominant IBS; the connection requires hormonal as well as digestive intervention for lasting resolution

Treatment and Optimization Strategy

SIBO Treatment as the Highest-Priority Intervention

When SIBO is identified on breath testing, treating the bacterial overgrowth directly with rifaximin (with or without neomycin based on gas type), herbal antimicrobial protocols, or elemental diet produces resolution of the fermentation-based symptom burden that no dietary or probiotic intervention alone can achieve. Post-SIBO prokinetic therapy to restore migrating motor complex function reduces the recurrence rate that makes SIBO a chronically relapsing condition in many patients.

What Most Doctors Miss

• SIBO as a treatable driver is almost never tested: studies consistently show that more than half of IBS patients have demonstrable bacterial overgrowth on breath testing; patients spend years on symptom management when a treatable microbial imbalance is driving the entire picture
• The gut-hormone connection, particularly in women: progesterone slows gut motility and the luteal phase of the menstrual cycle reliably worsens constipation-predominant IBS; perimenopausal and postmenopausal hormonal shifts profoundly alter gut function; these connections are acknowledged in research literature but almost never addressed clinically
• Histamine intolerance as a driver of IBS-like symptoms is systematically overlooked: many patients with IBS respond to high-histamine food categories (fermented foods, wine, leftovers, aged cheese) without realizing this represents a separate mechanism from FODMAP intolerance; low DAO activity is measurable and treatable
• Post-infectious IBS has specific diagnostic markers that are not tested: anti-CdtB and anti-vinculin autoantibodies from prior infectious gastroenteritis are identifiable and explain altered motility and visceral hypersensitivity; this subset requires a different approach than idiopathic IBS

When to Seek Medical Care

Chronic digestive symptoms lasting more than three months that are interfering with daily life warrant thorough evaluation rather than indefinite symptom management. Even if structural disease has been ruled out, the root cause of functional symptoms can be identified and addressed in the vast majority of patients.

Seek urgent evaluation for rectal bleeding, unintended significant weight loss, new symptoms after age 50, nocturnal symptoms that wake you from sleep, or a family history of colon cancer or inflammatory bowel disease. These features require colonoscopy and structural evaluation before functional diagnosis can be confirmed.

Recommended Testing

Frequently Asked Questions

How The Lamkin Clinic Approaches IBS

At The Lamkin Clinic, IBS evaluation goes well beyond ruling out structural disease. We systematically assess for SIBO, gut dysbiosis, intestinal permeability, food sensitivities, histamine intolerance, and the gut-brain axis components including cortisol dysregulation, vagal tone, and hormonal influences on gut motility. Treatment proceeds sequentially, addressing the most impactful upstream driver first.

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