SIBO That Keeps Coming Back

What the standard model gets wrong

The standard model treats SIBO as a primary microbial event. The clinical picture is attributed to bacteria in the wrong place, and the treatment is to remove them. Rifaximin, herbal antimicrobials, elemental diets, and motility agents are deployed against the overgrowth. The recurrence rate, across studies and across decades, is poor. A substantial fraction of patients relapse within months. The standard explanation is that the original eradication was incomplete, or that motility was inadequately supported, or that the patient is non-compliant.

None of those explanations survive contact with the case data. Patients relapse on full protocols, with documented motility, with strict adherence. The framework is the problem, not the patient. When eradication consistently fails to produce durable remission, the target is wrong.

The microbial signature is downstream. The bacteria are colonizing an environment that permits them. Until the environment is restored, no amount of antimicrobial pressure produces lasting change.

What the Host Capacity Model says about SIBO

A healthy colon maintains an oxygen gradient that is steep and stable. Colonocytes oxidize butyrate through beta-oxidation, consuming oxygen at the epithelial surface, and the lumen stays anaerobic. Strict anaerobes dominate, and facultative organisms — including the species that drive SIBO — are kept at low density. This is the default state. It is maintained, not given.

When colonocyte bioenergetics fail, butyrate oxidation drops. Oxygen consumption falls. Oxygen leaks into the lumen. The environment shifts from anaerobic to microaerobic, and facultative organisms now have a substrate to use. The microbial signature reorganizes upward through the GI tract. Small bowel populations expand. The breath test turns positive.

Why does butyrate oxidation fail? Several converging mechanisms. NAD+ depletion. Complex IV insufficiency. Iron-sulfur cluster failure in the electron transport chain. CD38-driven NAD+ consumption under chronic immune activation. Mitochondrial damage from prior viral or septic insult. Each of these reduces the colonocyte's capacity to oxidize butyrate, even when butyrate is present. Some patients have plenty of butyrate substrate and still cannot use it.

This is why SIBO recurs. The substrate the colonocyte runs on is butyrate. The capacity to use butyrate is bioenergetic. The bioenergetic lesion sits upstream of the microbial signature. You can clear the bacteria a hundred times. The environment remains permissive.

Treatment that addresses host capacity — restoring NAD+, supporting Complex IV, rebuilding the substrate environment, repairing barrier integrity — produces durable change. Antimicrobials are useful inside that window. They are not a stand-alone strategy.

Patterns I look for in cases like this

• Relapse within three months of completed eradication, regardless of agent.
• Worsening response to repeat courses of the same antimicrobial.
• Methane-dominant or hydrogen-sulfide patterns that drift over time.
• Concurrent histamine intolerance or mast cell features.
• Post-viral onset or symptom amplification after a confirmed infection.
• Energetic features the patient reports as fatigue, post-exertional malaise, or cognitive dimming.
• Bloating that is worse later in the day, consistent with progressive bioenergetic depletion.
• Disproportionate response to small amounts of fiber or fermentable carbohydrate.
• A history of antibiotic exposure followed by a different baseline that never recovered.
• Normal conventional labs with persistent symptoms.

Tests I usually want to see

• Organic Acid Test — Krebs cycle intermediates, lactate to pyruvate ratio, oxidative stress markers.
• Intracellular NAD+ panel — target above 500 μM, common to see below 350 in recurrent cases.
• Stool short-chain fatty acid panel — butyrate level and producer abundance.
• Shotgun metagenomics — Faecalibacterium, Roseburia, Akkermansia, sulfur-reducer load.
• Barrier markers — zonulin, LPS, LBP, calprotectin.
• SIBO breath test — for confirmation of pattern and substrate, not as a primary target.
• Iron and ferritin — iron-sulfur cluster context.
• hs-CRP, IL-6, TNF-α — for the immune-activation layer that drives CD38.

Leverage points

The highest-leverage intervention in recurrent SIBO is restoring colonocyte bioenergetic capacity. NAD+ restoration through NMN or NR at sufficient dose, sustained long enough to replete the intracellular pool, is the foundation. Without it, every other intervention is downstream rate-limited.

The second leverage point is rebuilding the substrate environment. Butyrate supplementation while colonocyte capacity recovers. Prebiotic introduction once tolerance is established. Polyphenol density in the diet. The goal is to re-seed the producers, not to chase the consumers.

The third leverage point is reducing the immune activation that drives CD38 overexpression and accelerates NAD+ consumption. This is where MCAS overlap, post-viral inflammation, and barrier-driven endotoxemia matter. Quieting the upstream drivers prevents the recovery from being eroded as fast as it is built.

Antimicrobials remain useful — to reduce load during the recovery window, to prevent symptom escalation, to give the host space to rebuild. Used this way, they support recovery. Used as the strategy, they perpetuate the cycle.

Where this account may be wrong

The Host Capacity Model is a candidate framework, not a settled one. It is evidence-tiered and reviewed. Major claims live on the Claim Ledger with their supporting citations and confidence levels. The honest scope is the cases in which colonocyte bioenergetic failure is the dominant upstream lesion. Some recurrent SIBO is driven by anatomic factors, adhesions, ileocecal valve dysfunction, or primary motility disease, and those cases need different reasoning. The framework is not a universal explanation. It is the most defensible mechanistic account of the largest subgroup.

Frequently asked questions

Related reading

• The Host Capacity Model
• Colonocyte bioenergetics
• Oxygen gradient failure
• Butyrate oxidation
• SIBO through the Host Capacity Model
• Why SIBO keeps coming back