SIBO: When the Story Doesn’t Match the Symptoms

Understanding patterns, testing choices, and therapeutic direction

There’s a moment in clinic most practitioners will recognise.The patient sits in front of you describing bloating that makes them look six months pregnant by evening, alternating bowel habits, food reactions that don’t quite follow logic, and a fatigue that feels disproportionate to their life.They’ve often been told it’s “just IBS.”But as clinicians, we learn fairly quickly: IBS is not a diagnosis. It’s a label for a pattern we haven’t yet explained. And more often than not, that pattern leads us to Small Intestinal Bacterial Overgrowth (SIBO).

What Is SIBO—Clinically Speaking?

SIBO is, at its simplest, bacteria living where they shouldn’t be—an overgrowth in the small intestine, where bacterial density should be relatively low.But clinically, it’s more nuanced than that.It’s not just presence—it’s function, fermentation, and gas production. 

Different organisms produce different gases, and those gases drive symptom patterns:

•  Hydrogen → bloating, loose stools

•   Methane (IMO) → constipation, slowed motility

•  Hydrogen sulphide → diarrhoea, urgency, often overlookedThis is where testing becomes essential—not just to confirm SIBO, but to differentiate its subtype.

Recognising the SIBO Pattern

While symptoms overlap with IBS, there are some key clinical clues:

•  Postprandial bloating (often within 30–90 minutes)

•  Food intolerances—especially FODMAPs

•   Alternating constipation and diarrhoea

•  Gas, distension, and pressure

•  Brain fog or fatigue after meals

•   Partial or temporary response to antimicrobials And perhaps most importantly:

The patient improves… but never fully resolves.

That’s often your signal that the root mechanism hasn’t been fully mapped.

Testing for SIBO: Choosing the Right Lens

At Colabs, we use four key tests—each answering a slightly different question.Think of them not as competitors, but as complementary tools in a clinical model.

1. IBS Smart Test – Is This Post-Infectious?

The IBS Smart test is often overlooked in SIBO workups—but it shouldn’t be.It measures two antibodies:

• Anti-CdtB

• Anti-vinculin

These are associated with post-infectious IBS, a common precursor to SIBO.

Why it matters clinically:

• Identifies autoimmune-driven motility impairment

• Suggests damage to the migrating motor complex (MMC)

• Explains why SIBO keeps recurring

This is the test that answers:

“Why did this patient develop SIBO in the first place?”

2. Aerodiagnostics SIBO Breath Test – The Traditional Workhorse

The Aerodiagnostics breath test represents the classic 2-gas model:

• Hydrogen

• Methane 

Like all breath tests, it works by:

1. Administering a sugar substrate (glucose or lactulose)

2. Measuring gases produced by bacterial fermentation

3. Tracking timing and rise in gas levels

Strengths:

• Widely used and well understood• Good for identifying hydrogen and methane patterns

• Useful baseline test in many cases

Limitations:

• Does not measure hydrogen sulphide

• May miss certain SIBO presentations

3. TrioSmart Breath Test – A More Complete Gas Picture

The TrioSmart test represents a significant step forward.

It measures three gases:

• Hydrogen

• Methane

• Hydrogen sulphide

This matters more than it might seem.

Hydrogen sulphide–producing organisms can consume hydrogen, masking results ontraditional tests.

Clinically, this means:

A patient can have:

• Classic SIBO symptoms

• A “normal” 2-gas test

…because the wrong gas wasn’t measured.

What TrioSmart adds:

• Detection of hydrogen sulphide SIBO (often missed)

• Greater clarity in complex or non-responsive cases

• More targeted therapeutic direction

This is often the test that answers:

“Why didn’t the previous treatment/therapeutic phase work?”

4. GI-MAP Stool Test – Looking Beyond the Small Intestine

SIBO doesn’t exist in isolation.

The GI-MAP stool test expands the picture by assessing:

• Microbial balance (commensals, opportunists, pathogens)

• Inflammatory markers

• Gut integrity (e.g. zonulin)

Why include stool testing in SIBO?

Because SIBO is often downstream of a broader ecosystem issue.

GI-MAP helps identify:

• Dysbiosis driving relapse

• Pathogens maintaining inflammation

• Gut barrier dysfunction

This is the test that answers : 

“What’s sustaining this pattern?”

Putting It Together: A Clinical Testing Strategy

Rather than choosing one test, think in layers:

1. IBS Smart → identifies underlying cause (post-infectious / autoimmune)

2. Breath test (Aero or TrioSmart) → defines gas pattern

3. GI-MAP → explores ecosystem and terrain

Not every patient needs all three—but in complex or chronic cases, this layered approachis often what shifts outcomes.

Therapeutic Considerations: It’s Not Just About Killing Bacteria

One of the biggest mistakes in SIBO treatment/therapeutics is working with it as a simpleinfection. It isn’t. It’s a functional disorder of motility, immunity, and microbial balance.

A more effective therapeutic model includes:

1. Reduce the Overgrowth

• Herbal antimicrobials or antibiotics

• Gas-specific strategies (e.g. methane vs hydrogen sulphide)

2. Restore Motility

• Prokinetics

• Addressing vagal tone

• Supporting the migrating motor complex

3. Repair the Terrain

• Gut lining support

• Address inflammation

• Rebalance the microbiome

4. Prevent Recurrence

• Address root cause (e.g. post-infectious autoimmunity)

• Personalised nutrition strategy

• Long-term motility support

Final Thoughts

SIBO is rarely just about bacteria.  It’s about patterns that haven’t yet been fully understood.And testing—when used well—doesn’t just confirm a diagnosis.It helps you understand the story behind the symptoms.At Colabs, our goal isn’t simply to identify SIBO.It’s to give practitioners the tools to ask:“What kind of SIBO is this—and why is it here?”Because that’s where therapeutics become more precise.And outcomes start to change.