CIRS and Gut Health: Why Mycotoxins Often Trigger Digestive Issues

What Mycotoxins Do to your Gut Lining

Your intestinal wall is not a simple barrier. It’s a layered system; a combination of physical, chemical, immunological, and microbial systems all working together to let nutrients in and keep harmful things out. Mycotoxins compromise every layer of that system.

The research here is fairly clear. A 2020 review published in Toxins documented the specific mechanisms through which common mycotoxins,  including deoxynivalenol, aflatoxins, and ochratoxin A, damage the gut: they degrade epithelial cells, reduce the expression of tight junction proteins, thin the mucosal layer, and trigger a cascade of inflammatory signalling that destabilizes intestinal immunity. (Source)

Tight junctions are the protein “clasps” that hold intestinal cells together and regulate what moves through the wall. When mycotoxins break those down, the result is increased intestinal permeability. Something you probably know as leaky gut. Once the barrier is compromised, partially digested food particles, bacteria, and more mycotoxins can translocate into systemic circulation, driving inflammation well beyond the gut itself.

If you’ve ever done an IgG food sensitivity panel and had reactivity to just about every food listed, it’s not a food issue. It’s a compromised gut barrier

A related review in the International Journal of Molecular Sciences confirmed this across multiple mycotoxin types and multiple species models, concluding that mycotoxin-induced barrier disruption results in both bacterial translocation and activation of systemic and local immune responses. (Source)

This is not a subtle effect. These are measurable structural and functional changes to your intestinal architecture. And these changes don’t resolve simply by leaving a moldy building or taking a binder. Nor is it as simple as supplementing gluatamine and cod liver oil.

Mycotoxins Disrupt your Microbiome

Gut dysbiosis is not just about eating too much sugar or taking antibiotics. Mycotoxin exposure is a significant and under-recognized driver of microbiome disruption.

A comprehensive review in Toxins (2020) examined the bidirectional relationship between mycotoxins and gut microbiota. The conclusion is important: mycotoxin exposure shifts the population equilibrium of the gut, depleting beneficial species and creating conditions where opportunistic bacteria and fungi can expand. The review notes this disruption is linked to bacterial translocation and the onset of chronic inflammatory disease. (Source)

A 2018 review in Frontiers in Microbiology reinforced this, summarizing evidence that mycotoxins produce measurable perturbations in the intestinal epithelium and microbiota. Including reduced biodiversity and increased susceptibility to pathogenic colonization. (Source)

What this looks like clinically is a gut that can’t defend itself. Beneficial species like Lactobacillus and Bifidobacterium decline. Short-chain fatty acid production drops, meaning less butyrate to fuel the intestinal lining and regulate inflammation. Opportunistic organisms fill the gap.

This is where SIBO, SIFO, fungal overgrowth, and recurrent parasitic infections enter the picture. Not as separate bad luck, but as predictable consequences of a gut that has lost its microbial defence.

Remember, these “infections” are caused by a lack of beneficial bacterial species and a decline of SCFA (short-chain fatty acids). What this means clinically, is that more anti-microbial protocols ARE NOT the answer. Utilizing antimicrobials will destroy even more of the Lactobacillus and Bifidobacterium species in your gut which perpetuates your GI issues.

To be clear, I’m not opposed to using antimicrobials. In fact, I often think them to be necessary. But like most things with CIRS, proper sequencing is essential.

Why CIRS Often Looks Like SIBO, SIFO, or Chronic Gut Infection

I see this pattern every week in the clinic. A phone call with a new patient describing  having already treated SIBO maybe two or three times. Then they develop SIFO. Then a parasitic infection clears, but SIBO comes back. Each treatment works temporarily, then unravels.

The reason isn’t bad luck poor compliance, or improper treatment. It’s that the underlying conditions driving those overgrowths were never corrected. Remember, sequencing is essential in CIRS treatment. The right intervention and the wrong time doesn’t work.

In CIRS, the biotoxin inflammatory pathway creates near-perfect conditions for gut dysfunction. Motility slows, which encourages bacterial buildup in the small intestine. Mucosal immunity weakens, reducing the gut’s ability to resist colonization by pathogens. Bile flow and antimicrobial defenses are impaired. Chronic inflammation disrupts digestion and absorption at every level.

A 2023 review in Microorganisms examining the relationship between gut dysbiosis and conditions like SIBO, SIFO, and intestinal methanogen overgrowth,  found that increased intestinal permeability and LPS-driven inflammation are consistently implicated in driving microbial overgrowth. (Source)

Treating each overgrowth without addressing that underlying physiology is like draining a flooded room without turning off the tap.

The MSH Connection: The Missing Piece Most Clinicians Overlook

MSH is the most important hormone you and your functional medicine doctor have never heard of. Of all the biomarkers disrupted in CIRS, MSH (melanocyte-stimulating hormone) is the one most directly tied to gut health. And it’s the one that most providers have never heard of.

MSH is a neuropeptide derived from POMC (proopiomelanocortin). It regulates immune balance, gut motility, mucosal integrity, appetite, pain regulation, sleep, and inflammation control. In CIRS, MSH is consistently low and research has established this as a defining feature of the condition. A review published in PMC in 2024 confirmed that reduced MSH is a consistent finding in patients with chronic biotoxin-related illness, and that it functions as a master controller within the neuroimmune regulatory network. (Source)

What does low MSH mean for the gut specifically?

A 2017 study in PLOS ONE tested this directly. Using human Caco-2 intestinal epithelial monolayers, researchers found that alpha-MSH protects the intestinal barrier against cytokine-induced damage, preserving tight junction protein expression (ZO-1 and claudin-4), reducing intestinal permeability, and suppressing NF-kB activation and downstream inflammatory cytokine production. When MSH was present, the barrier held. When inflammatory cytokines acted alone, it broke down. (Source)

Research has also established MSH’s role in gut motility. A review in the Journal of the Chinese Medical Association documented that alpha-MSH influences small intestinal transit and colonic motility through central melanocortin receptor signaling. Meaning that low MSH in CIRS directly impairs the gut’s ability to move contents through at a normal rate. Slowed motility is one of the primary drivers of SIBO. (Source)

The clinical implication is significant. Without adequate MSH, the gut lining is more vulnerable, motility is impaired, and the microbiome is harder to stabilize. No amount of probiotics, antimicrobials, or dietary intervention can fully compensate for a depleted neuroimmune regulatory signal.

Why I Recommend Treating CIRS Before Gut-Only Protocols

The analogy I use with patients: trying to heal the gut before treating CIRS is like painting a wall while water is still pouring through the ceiling. The work won’t hold.

Here’s the physiology behind that.

The biotoxin inflammatory pathway in CIRS remains active until CIRS is treated. That means inflammation keeps the microbiome destabilized. Antimicrobial and antifungal protocols produce temporary results because the conditions that allow overgrowth are never resolved. Low MSH means the gut lining cannot repair itself regardless of diet, binders, or supplements.

CIRS patients also commonly react severely to gut protocols: nausea, increased bloating, worsening brain fog, fatigue, anxiety. These reactions soften significantly once the underlying inflammatory cascade is addressed and MSH begins to normalize.

The Shoemaker Protocol, the only treatment for CIRS with documented clinical efficacy in the peer-reviewed literature,  addresses CIRS systematically: removing biotoxin exposure, clearing biotoxins, correcting inflammatory biomarkers, and restoring neuroendocrine balance including MSH. A 2024 literature review confirmed that across 13 identified treatment studies, the Shoemaker Protocol was the only approach with evidence of reversing the underlying physiological dysregulation of CIRS. (Source)

As MSH and cytokine patterns normalize through this process, what I observe clinically is:

Gut permeability decreases. Motility normalizes. Microbiome diversity increases. Bile flow and digestive enzyme function improve. Food sensitivities soften. SIBO and SIFO relapse rates drop considerably. The gut becomes a system that can actually respond to treatment.

A Practical Roadmap

Here’s the sequence I recommend for patients who present with both CIRS and significant GI issues.

Step 1: Evaluate for CIRS. Use symptom cluster analysis, exposure history, VCS testing, and laboratory biomarkers through a trained provider. Don’t skip this step. Treating chronic gut symptoms as a standalone problem without ruling out CIRS is one of the most common reasons patients cycle through protocols without resolution.

Step 2: Treat CIRS first. Follow the Shoemaker Protocol in sequence: remove exposure, bind biotoxins, correct biomarkers, restore neuroimmune balance. MSH restoration is particularly critical for gut outcomes.

Step 3: Reassess gut function. Once inflammation has dropped and MSH has stabilized, many gut symptoms resolve without additional intervention. Reassess what actually remains before layering in new protocols.

Step 4: Targeted gut support where needed. This may include probiotics (when tolerated), digestive enzyme support, mucosal repair nutrients, motility agents, and antimicrobials if truly necessary. The difference at this stage: your body can actually tolerate and respond to these interventions.

Step 5: Long-term maintenance. Ongoing exposure avoidance, supporting circadian rhythm, nourishing microbiome diversity, and mitochondrial health support are the foundation of sustained recovery.

Final Thoughts

If you’ve been treating your gut over and over without lasting results, the missing variable may not be the protocol. It may be that the system driving the problem was never addressed.

CIRS-driven inflammation, low MSH, disrupted mucosal immunity, and impaired motility create a setup for chronic digestive symptoms that gut treatments alone cannot resolve. When you treat the root cause (low MSH levels)  the gut often heals in ways that years of GI protocols couldn’t produce.

That’s not guesswork. That’s what the physiology predicts, and what I see in the clinic.

If this is your first introduction to CIRS, be sure to check out my other posts to further your CIRS knowledge:

• What Is CIRS?
• Symptoms of CIRS
• How Is CIRS Diagnosed?
• The CIRS Treatment Protocol

Dr. Mark Volmer is the Clinical Director of Flourish Clinic and the creator of The Mitochondria Mechanic — patient education for CIRS and complex chronic illness. He treats patients across Canada using the Shoemaker Protocol.