Digestive symptom

SIBO (Small Intestinal Bacterial Overgrowth) and your gut: which markers and tests to look at

SIBO is bacterial overgrowth in the small intestine, where bacteria should be present in much lower numbers than the colon. The classic presentation is bloating that worsens through the day, post-meal distension within 30 to 90 minutes, and either constipation (methane-dominant, now called Intestinal Methanogen Overgrowth or IMO) or diarrhea (hydrogen-dominant). SIBO is technically diagnosed by a hydrogen and methane breath test, not a stool test. But a stool test still adds useful context: elevated Methanobrevibacter smithii on a stool test is highly correlated with positive methane breath testing, and stool tests catch the dysbiosis and host marker changes that often coexist with SIBO.

See a doctor first if you have any of these

rapid unintended weight loss
severe nutrient deficiencies (B12, fat-soluble vitamins)
blood in stool
uncontrollable diarrhea

These symptoms warrant clinical evaluation before any food protocol. The rest of this page assumes you've ruled them out.

The gut markers most often behind sibo (small intestinal bacterial overgrowth)

Ordered by how frequently they appear in the literature for this symptom. Click any underlined marker to see what the result means and how to address it.

1
Elevated Methanobrevibacter smithii
2
Klebsiella pneumoniae (detail page coming soon)
3
Streptococcus spp. (detail page coming soon)
4
Pancreatic Elastase-1 (detail page coming soon)
5
Low Secretory IgA

Tests best suited to find them

Listed in priority order. Tests with PDF upload support get you a full personalized protocol the same day you upload.

Diagnostic Solutions Laboratory · Upload supported GI-MAP Genova Diagnostics · Upload supported Genova GI-Effects

Already have a stool test PDF?

Upload your GI-MAP, Genova GI-Effects, or Biomesight result and we'll extract every marker behind your sibo (small intestinal bacterial overgrowth) and generate a personalized 6-week food protocol with exact quantities.

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Non-gut causes worth ruling out first

SIBO (Small Intestinal Bacterial Overgrowth) is not always gut-driven. Before assuming the cause is in your microbiome, work through these:

structural causes (adhesions from prior surgery, strictures, diverticula)
low stomach acid (often from PPIs or chronic stress)
ileocecal valve dysfunction
diabetes or any condition that slows gastric emptying
chronic narcotic or anticholinergic use

Low-cost things to try this week

These are reasonable first moves while you decide whether to test or wait. None of them require a prescription or a kit.

Order a 3-hour hydrogen and methane breath test for direct diagnosis
Stop any unnecessary acid blockers (PPIs) under physician guidance
Eat 3 distinct meals with 4-hour spacing, no constant snacking, to allow the migrating motor complex to clear the small bowel
Try 4 weeks of low-FODMAP as a symptom probe

Frequently asked questions

Is sibo (small intestinal bacterial overgrowth) always caused by gut problems?

No. The gut connection is real and often underdiagnosed, but the page above lists non-gut causes worth ruling out first. Going straight to a stool test without considering thyroid, anemia, sleep, or medication side effects can mean treating the wrong thing.

Which test is best for sibo (small intestinal bacterial overgrowth)?

The recommended tests above are listed in priority order. The general rule: GI-MAP and Genova GI-Effects are the higher-yield choices when the suspected drivers are infections, opportunistic overgrowth, or host-marker patterns. 16S sequencing tests like Biomesight or Thorne are better for diversity and ecology questions.

How long until I see improvement once I start a protocol?

Symptom-level changes usually appear within 2 to 3 weeks of starting a targeted dietary protocol. Marker-level changes take longer, typically 8 to 12 weeks, which is the validated retest window for most stool-test panels.

Can I skip the test and just try a generic protocol?

You can. The trade-off is that sibo (small intestinal bacterial overgrowth) has multiple possible drivers and the food protocols differ between them. A test costs less than 6 to 12 weeks of trying the wrong protocol. If budget is the constraint, the lowest-cost meaningful test in this category is Biomesight (around $130 to $180).

When should I see a doctor instead of self-investigating?

The red flags listed above are the cases where a doctor visit comes first. Anything else is reasonable to investigate with a stool test, but a doctor visit in parallel with the gut work is almost always the right move when symptoms are persistent.