Overgrowth, dysbiosis & antimicrobials
One of 5 mechanistic pathways to 🦠 Gut health & digestion · 22 options
SIBO, SIFO and H. pylori all involve organisms in the wrong place or in the wrong numbers. This is the pathway where prebiotics make things worse and where the sequence — kill, then clear biofilm, then re-establish motility — determines whether it comes back.
SIBO's signature is a HIGH folate with a low B12 — the overgrown bacteria produce folate and consume B12. That combination on a standard panel is a genuine clue and almost nobody reads it.
Complete Blood Count (CBC) with Differentialhs-CRP (High-Sensitivity C-Reactive Protein)Vitamin B12Folate, SerumComprehensive Metabolic Panel (CMP)🌱 Gut Health & Absorption covers these in one panel →
What engages this pathway
Ordered by how directly each one acts on the mechanism above — never by how much trial evidence exists. Each links to its full breakdown with dosing, half-life and vendor.
🧬 Oregano Oil
Carvacrol has broad antimicrobial activity, and one trial found herbal antimicrobials non-inferior to rifaximin in SIBO. Non-selective, so it hits commensals too.
🧬 Berberine
Antimicrobial as well as metabolic — a component of most herbal SIBO protocols.
🧬 Allicin
Stabilized allicin has particular activity against methane-producing archaea, which is the hardest SIBO subtype to treat.
🧬 Neem
Traditional antimicrobial used in the same protocols.
🧬 Caprylic Acid
Disrupts fungal cell membranes; used for Candida overgrowth.
🧬 Undecylenic Acid
Antifungal fatty acid with better mucosal persistence than caprylic acid.
🧬 Monolaurin
Disrupts lipid-enveloped organisms — viruses and some bacteria.
🧬 Wormwood
Traditional antiparasitic; thujone content means duration limits matter.
🧬 Black Walnut Hull
Traditional antiparasitic, usually combined with wormwood and clove.
🧬 Grapefruit Seed Extract
Broad claims, and a long documented history of products being adulterated with synthetic preservatives that were doing the actual antimicrobial work.
🧬 Mastic Gum
Human trials exist and they disagree: a randomized pilot found an effect on H. pylori, and a separate in-vivo study found no effect on bacterial load at all (PMID 12888582). The steadier signal is symptomatic relief in dyspepsia. Supportive, not an eradication therapy.
🧬 Olive Leaf Extract
Oleuropein with broad antimicrobial activity in vitro.
💉 LL-37
An endogenous antimicrobial peptide that also disrupts biofilm — the reason resistant overgrowth persists through antibiotics.
🧬 Saccharomyces boulardii
Competitively excludes pathogens and is unaffected by antibacterials, so it can run throughout.
🧬 L. reuteri
Produces reuterin, an antimicrobial that suppresses gram-negative organisms without stripping the commensals — which is the argument for running it alongside an eradication protocol rather than instead of one. The H. pylori data is the strongest part of that case, and it is adjunct data, not monotherapy.
🧬 Bismuth Subsalicylate
Biofilm disruption and antimicrobial activity; a standard component of H. pylori regimens.
🧬 Serrapeptase
Proposed biofilm disruptor. The rationale is better than the evidence.
🧬 D-Mannose
Binds E. coli fimbriae so bacteria are flushed rather than killed — genuinely elegant, and it has trial evidence for recurrent UTI without driving resistance.
🧬 Cranberry (PACs)
Proanthocyanidins prevent E. coli adhesion to the urothelium. Meta-analysis supports prevention of recurrent UTI — prevention specifically, not treatment of an active one.
🧬 Pau d'Arco
Lapachol and naphthoquinones with antifungal and antibacterial activity in vitro. Traditional use is long; human trials are absent and high doses are toxic.
🧬 GI Relief
A formulated blend for acute gut irritation — demulcents plus anti-inflammatories.
🧬 Diatomaceous Earth
Food-grade amorphous silica marketed as a parasite treatment on a mechanical-abrasion theory that has no human evidence behind it. Inhalation of the powder is a genuine lung hazard.
What actually decides this outcome, in order of size
Twenty-one antimicrobials on one page, and the largest determinant of whether any of them helps is upstream of all of them: whether the diagnosis is real, and whether the thing that caused it is still there.
- Whether the breath test meant anything. Hydrogen and methane breath testing carries a formal North American consensus precisely because the substrate, the dose, the timing and the positivity threshold all vary between laboratories Rezaie 2017. A 90-minute lactulose rise can be small-intestinal fermentation or it can be accelerated transit delivering substrate to the colon early. Those are opposite diagnoses from one curve.
- The mechanical cause, which antimicrobials do not touch. Overgrowth is usually secondary: a migrating motor complex that has stopped, an adhesion, a blind loop, a stricture, an ileocecal valve that no longer closes, or 20 mg/day of a proton-pump inhibitor removing the acid barrier. Kill the organisms and leave the cause and you have bought a 3-month remission.
- Which gas, because it changes the drug. Hydrogen and methane are produced by different organisms, methane by archaeal methanogens rather than bacteria, and the methane picture is constipation-predominant while the hydrogen picture is diarrhea-predominant.
- The migrating motor complex, which is the mechanism this whole page depends on. Phase III of the interdigestive cycle sweeps the small intestine every 90 to 120 minutes, but only in the fasted state, so continuous grazing abolishes it. A 4-hour gap between meals and 12 hours overnight is the cheapest antimicrobial here.
- The one antimicrobial with phase 3 data in this space. Rifaximin, a non-absorbed rifamycin, gave adequate relief of global IBS symptoms in 40.8% against 31.2% on placebo in TARGET 1 (P=0.01) and 40.6% against 32.2% in TARGET 2 (P=0.03), 40.7% against 31.7% combined (P<0.001) Pimentel 2011. A 9-point absolute difference is the realistic ceiling for killing things in this compartment.
- What you feed afterwards. The low FODMAP diet reduces fermentable substrate and is the best-tested dietary lever here Black 2022, and this is the one pathway on the site where prebiotic fiber is the wrong move rather than the right one.
The order to run these in, and what has to be true first
The pathway's own `why` names the sequence: kill, clear biofilm, then reseed. Two steps go in front of it.
- Confirm the diagnosis and read the test critically. Know the substrate, the threshold and the 90-minute rule before you accept a positive Rezaie 2017. Exclude the mimics once: Complete Blood Count (CBC) with Differential, hs-CRP (High-Sensitivity C-Reactive Protein), Ferritin read beside CRP because ferritin is an acute-phase protein Luo 2023, Vitamin B12 with Methylmalonic Acid (MMA) because overgrowth consumes B12 while producing folate, and Folate, Serum, where a high folate with a low B12 is a classic overgrowth signature.
- Find and fix the cause. Stop the unnecessary proton-pump inhibitor, treat the hypothyroidism slowing transit (TSH (Thyroid-Stimulating Hormone), Free T4 (Thyroxine)), and ask whether an abdominal surgery in the history left an anatomical answer that no capsule reaches.
- Then the antimicrobial phase, 2 to 4 weeks and time-limited. Oregano Oil for its carvacrol and thymol content, Allicin which is the one with the strongest case against methanogens, Berberine which is also an AMPK activator and doubles as a glycemic agent, Neem, Wormwood, Olive Leaf Extract and Caprylic Acid for the fungal picture with Undecylenic Acid.
- Dose the antifungal arm on its own terms. Caprylic Acid is an 8-carbon medium-chain fatty acid that partitions into fungal membranes and is absorbed in the proximal small intestine, so an enteric or delayed-release form is what reaches the distal bowel at all. Undecylenic Acid is the 11-carbon analog with the same argument.
- Then biofilm and the stomach-specific cases. Serrapeptase and Monolaurin target the matrix rather than the organism; Mastic Gum and Bismuth Subsalicylate are the Helicobacter pylori pair, and bismuth is a component of real quadruple therapy rather than a substitute for it.
- Then reseed and refeed, in that order. Saccharomyces boulardii is a yeast and survives antibacterials, which is why it goes first. Reintroduce fermentable fiber slowly afterwards Black 2022. D-Mannose and Cranberry (PACs) are urinary rather than intestinal and are on this page because the organisms overlap.
What gets bought for this that cannot move it
Prebiotic fiber is the wrong move here, and it is the commonest thing bought for a gut complaint. Feeding fermentable substrate to an overgrown small intestine produces hydrogen and methane exactly where you do not want them. The reduction of fermentable substrate is the mechanism of the best-tested diet in this space Black 2022, which is the opposite instruction.
Killing without fixing the cause buys about 3 months. Recurrence after successful eradication is the rule when the migrating motor complex, the anatomy or the acid barrier is unchanged. A second and third antimicrobial round for a recurrence is treating the same untreated cause a second and third time.
Diatomaceous Earth, Pau d'Arco and Grapefruit Seed Extract are the three weakest entries here. Grapefruit seed extract preparations have repeatedly been found to owe their activity to added preservatives rather than to the fruit, and diatomaceous earth is amorphous silica with a mechanical rationale and no human trial in this indication. They are on the page for completeness, and this is what completeness costs.
Herbal antimicrobials are not gentler, they are less characterized. Oregano oil and berberine are broad-spectrum antibacterials with real activity; the reason they read as safer is that nobody has run the trial that would show what they cost the colonic microbiome. Rifaximin's advantage is that it is under 0.4% systemically absorbed and has been measured Pimentel 2011.
And if the bloating is worse with stress and better on holiday, with no antibiotic history and a normal breath test, this is the wrong pathway. That is the brain-gut picture, where a behavioral therapy matched a structured diet head to head, and it lives on the motility pathway.
How you would know it was working, on a real read-out and a real timescale
The read-out here is unusual because the marker most people want to repeat, the breath test, is the one worth repeating least.
- A 14-day symptom diary of bloating timing, stool form and post-meal distension, before and after each 2-to-4-week round. Time-to-bloat after a meal is the most specific personal signal and it costs nothing.
- Vitamin B12 with Methylmalonic Acid (MMA) and Folate, Serum at 12 weeks. Small-intestinal bacteria consume B12 and synthesize folate, so a low B12 with a high folate is the biochemical fingerprint, and it should move as the overgrowth clears. MMA is the functional confirmation because serum B12 rises within 24 hours of any oral dose.
- Ferritin and Complete Blood Count (CBC) with Differential at 12 weeks, with hs-CRP (High-Sensitivity C-Reactive Protein). Overgrowth and inflammation both impair iron absorption at the duodenal enterocyte, and ferritin is an acute-phase protein that rises with the inflammation it is supposed to be independent of Luo 2023.
- Repeat breath testing at 6 to 12 weeks, and only where it will change what you do. The consensus exists because thresholds and substrates differ between laboratories Rezaie 2017, so a repeat on a different machine is not a comparison.
- Weight and stool form weekly through any 4-week round. Unintended weight loss during an antimicrobial course is a signal to stop and reconsider, because malabsorption and inflammatory bowel disease both present here and neither is treated by a 2-to-4-week herbal course.
- TSH (Thyroid-Stimulating Hormone) at 6 to 8 weeks if hypothyroidism was the mechanical cause. The pituitary integrates thyroid hormone over about 6 weeks.
What will fool you. Almost everything on this page also reduces intake, because antimicrobial herbs at therapeutic doses suppress appetite and cause nausea, and eating less relieves bloating on its own. A die-off reaction in the first 3 to 5 days is indistinguishable from an adverse reaction. And the low FODMAP diet run alongside a 4-week antimicrobial round means you will never know which of the two worked.
Sources read for these sections
- Rezaie A. Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus. American Journal of Gastroenterology 2017;112(5):775-784 · PMID 28323273
- Pimentel M, et al. Rifaximin therapy for patients with irritable bowel syndrome without constipation. New England Journal of Medicine 2011;364(1):22-32 · PMID 21208106
- Black CJ. Efficacy of a low FODMAP diet in irritable bowel syndrome: systematic review and network meta-analysis. Gut 2022;71(6):1117-1126 · PMID 34376515
- Luo H, et al. A Practical Guide to Adjust Micronutrient Biomarkers for Inflammation Using the BRINDA Method. Journal of Nutrition 2023 · PMID 36792034
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Frequently asked questions
SIBO, SIFO and H. pylori all involve organisms in the wrong place or in the wrong numbers. This is the pathway where prebiotics make things worse and where the sequence — kill, then clear biofilm, then re-establish motility — determines whether it comes back.
22 options are mapped to this pathway in the Vault, including Oregano Oil, Berberine, Allicin, Neem. They are grouped by the mechanism they act through rather than ranked by how much trial evidence exists — 10 carry clinical validation and 12 are mechanistic predictions.
SIBO's signature is a HIGH folate with a low B12 — the overgrown bacteria produce folate and consume B12. That combination on a standard panel is a genuine clue and almost nobody reads it. The markers worth checking are Complete Blood Count (CBC) with Differential, hs-CRP (High-Sensitivity C-Reactive Protein), Vitamin B12, Folate, Serum.
Unproven is not the same as ineffective. Of the 22 options on this pathway, 10 have clinical validation and 12 are graded theoretical — meaning the mechanism is sound but the specific human trial has not been run, which is true of a great deal of what works in this space. Nothing on this page is ordered by evidence tier, because sorting by trial count would bury the compounds you came looking for.
Where this goes next
Everything above is the free case for Overgrowth, dysbiosis & antimicrobials. The protocol — the dosing, the order to correct things in, the week-by-week schedule and what to retest — is a lesson inside Skool.