Why your gut health is an immune issue

Did you know that the most overlooked driver of many gut disorders is actually an imbalanced immune system?

When dealing with chronic issues like SIBO (small intestinal bacterial overgrowth), yeast overgrowths, parasites, or H. pylori ulcers, our immediate instinct is to treat it like a "seek and destroy" mission - identify the bad guy and kill it off, or ruthlessly cut out foods as a way of easing symptoms. But focusing solely on the invaders (or offending foods) ignores the real culprit: a dysfunctional immune response.

And in conditions such as inflammatory bowel disorders or autoimmune conditions, the conventional approach is often simply to suppress the immune system or do nothing at all.

The functional medicine shift that achieves results

Shifting our focus from endless eradication and suppression protocols to actively supporting and regulating the immune system changes everything. This is the core of a functional medicine approach.

In my clinic, I find this approach transformational in helping my clients truly to heal. By identifying the root cause, we can guide the body to restore equilibrium (homeostasis) and finally say goodbye to chronic health issues for good.

To understand how this works, let's take a brief look at how your immune system actually interacts with your digestive system, and how disorders can arise when things go awry.

Why your gut health is an immune issue

We possess an extraordinary, built-in defence network that is constantly scanning our environment for threats and dealing with them second-by-second. If we didn’t, we would have perished almost the moment we were born.

Your digestive tract is the single largest interface between your body and the outside world. This is exactly why between 70% and 80% of your immune system resides right there in your gut walls.

When you view chronic gut conditions through this lens, you can see how immunity must have a major role to play in recovery. Firstly, infections (bacterial, viral, parasitic) aren't just random bad luck; they are a symptom of a defence system that has lost its footing or has become overwhelmed. Secondly, rampant inflammation and autoimmunity are a clear sign that your immune system has become imbalanced.

Not just Invaders, but civil war

Invaders

In a healthy gut, our first line of defence is stomach acid. Most bacteria, yeasts, parasites, and viruses are destroyed here before they can travel any further into the digestive tract.

Any pathogens that do manage to slip past this barrier are quickly detected by immune cells constantly patrolling the gut lining. This triggers the production of targeted antibodies that act like visual flags, marking the intruders and signaling your white blood cells to swarm, engulf, and destroy them.

This system is incredibly sophisticated. In the case of overgrowths like SIBO or Candida, the bacteria and yeasts involved are actually normal residents of the gut. Yet, our immune surveillance system cleverly identifies when their numbers are getting out of hand.

A specialised type of antibody, known as secretory IgA, is key in this process - it is deployed to bind to these organisms, preventing them from sticking to the gut wall and bringing the overgrowth back under control. This same mechanism occurs in preventing pathogens, such as viruses, from taking hold.

SIgA is a major focus in nutritional therapy approaches as it is often depleted in those with gut disorders. There are several very simple, natural interventions that can help to restore levels of this antibody, such as specific probiotics and managing stress.

How do immune system breaches occur?

When our immune system is compromised or lacking the resources it needs, these vital defence mechanisms break down.

While gut health is a largely an immune issue here, low stomach acid is also a significant factor. In the case of Helicobacter pylori (H. pylori) infection, primarily responsible for stomach and duodenal ulcers, this commonly occurs when the environment in the stomach is too alkaline.

Amazingly, this nasty bug actively neutralises your stomach acid to keep the environment in its preferred alkaline state. This opens the gateway for other infections to take hold, e.g parasites, and this is one reason why those suffering gut issues often have more than one condition concurrently.

While there are several underlying causes, the most common drivers we see clinically include:

• Nutrient deficiencies: Lacking the foundational building blocks (like zinc and protein) needed to manufacture immune cells and stomach acid.

  
  

• Chronic stress: Cortisol actively suppresses your immune system and down-regulates stomach acid production.

  
  

• Medications: Especially proton pump inhibitors (PPIs) and antacids, which reduce your stomach acid levels.

Civil war

This occurs when the immune system stops being a protector and starts becoming the aggressor.

1. The bystander effect in IBD

In inflammatory bowel diseases (IBD), namely Crohn's disease and ulcerative colitis, the immune system starts attacking normal bacteria residing in the mucosal layer of the gut lining. The gut lining then becomes collateral damage as a result of the immune system's natural inflammatory mechanisms.

This is why IBDs are termed immune-mediated rather than autoimmune; the immune system is targeting the bacteria, and the body’s own tissue is simply caught in the cross-fire.

2. The autoimmune factor: coeliac disease

Coeliac disease is a true autoimmune condition where the body's immune system mistakenly attacks an enzyme in the gut called tissue transglutaminase (tTG).

The chain of events starts when immune cells flag gluten as a dangerous invader. However, because the tTG enzyme naturally binds to gluten as part of the digestive process, the immune system begins to confuse the two. Through a phenomenon known as molecular mimicry, the antibodies produced to fight gluten start targeting the tTG enzyme instead.

This "civil war" results in the destruction of the gut lining, leading to the flattening of the villi, the finger-like projections through which nutrients are absorbed. The resulting nutrient deficiencies compromise the immune system further, which can lead to a double-whammy of chronic overgrowths and gut infections (like SIBO or parasites) occurring alongside coeliac disease.

The domino effect: How autoimmune issues impact the gut

Other autoimmune conditions can trigger a dysfunctional domino effect where gut health becomes indirectly compromised. If you already have one autoimmune diagnosis, your immune system is already "primed," meaning it has lost a degree of self-tolerance. This makes you statistically more likely to develop additional autoimmune responses - and your gut often pays the price.

The metabolic brake: Hashimoto’s thyroiditis and SIBO

A good example of this connection is Hashimoto’s - an autoimmune thyroid condition that significantly increases your risk of developing SIBO. In this scenario, the mechanism is primarily metabolic:

• Slowed peristalsis: The immune attack on the thyroid slows down your entire metabolic rate. Because your digestive muscles rely heavily on active thyroid hormones to fuel peristalsis, your gut motility becomes sluggish. This forces food to move through the digestive tract much more slowly during and after meals, creating a stagnant environment where resident bacteria can ferment the food and rapidly multiply in the small intestine.

  
  

• The housekeeper function goes on strike: To make matters worse, the migrating motor complex (MMC)—the sweeping "cleansing wave" that acts as a housekeeper to clear out bacteria and debris between meals—also stalls when thyroid hormones drop. Without this crucial fasting cleanup cycle, residual food debris is left behind to be fermented by bacteria, fueling the overgrowth.

Both scenarios can trigger nasty symptoms of gas and bloating.

Post-infectious IBS & anti-vinculin antibodies

While Hashimoto's physically slows the gut down via hormones, there is another, more insidious autoimmune pathway that directly inhibits the MMC.

This is the classic "Bali Belly" or food poisoning trigger. When you are exposed to food-borne bacteria like Salmonella, Campylobacter, or E. coli, they release a toxic protein called CdtB. 

Your immune system naturally creates antibodies to destroy it. However, in susceptible individuals, a case of mistaken identity called molecular mimicry occurs. The CdtB toxin looks remarkably similar to vinculin—a vital human protein that powers the nerves behind the MMC's cleansing wave. The confused immune system begins manufacturing anti-vinculin antibodies, launching an autoimmune attack against its own enteric nervous system.  

With the vinculin proteins damaged, the MMC is functionally paralysed, allowing bacteria to migrate upward and proliferate into SIBO. This phenomenon is the primary driver behind post-infectious IBS, which typically presents as:  

• Hydrogen-dominant SIBO

• IBS-D (diarrhoea-dominant)

• IBS-M (mixed constipation and diarrhoea)

  
  

Connecting the dots: Autoimmune vulnerability

It is vital to understand that anti-vinculin autoimmunity isn't exclusive to Hashimoto’s, nor does Hashimoto's cause it directly. Rather, they are partners in crime.

If you have any pre-existing autoimmune condition, whether it is Hashimoto's, coeliac, or rheumatoid arthritis, your immune system is already hyper-reactive. If you get a bout of food poisoning, you are at a much higher risk of your immune system misidentifying vinculin and triggering this secondary, gut-specific autoimmune response. 

Supporting your motility: prokinetics

To help stimulate and restart the cleansing wave, supplements known as prokinetic agents are often required long-term. While there are pharmaceutical options, there are also highly effective natural prokinetics perfectly suited for ongoing use.

I highly recommend ginger capsules, which you can purchase directly in our online store. For maximum efficacy, these should be taken at least two hours away from food to target the MMC while the gut is empty.

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Testing

There is a blood test called IBS Smart that detects the antibodies responsible for post-infectious IBS. Unfortunately, it is not currently available in Australia.

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Don't give up

This disease pathway sounds quite alarming, but the good news is that there are plenty of natural interventions that can support healthier gut immune function.

References

Mantis, N. J., Rol, N., & Corthésy, B. (2011). Secretory IgA's complex roles in immunity and mucosal homeostasis in the gut. Mucosal immunology, 4(6), 603–611. https://doi.org/10.1038/mi.2011.41

Moreno-Sabater A, Sterlin D, Imamovic L, Bon F, Normand AC, Gonnin C, Gazzano M, Bensalah M, Dorgham K, Ben Salah E, Acherar A, Parizot C, Rigourd V, Begue H, Dalle F, Bachmeyer C, Hennequin C, Yssel H, Malphettes M, Fieschi C, Fadlallah J, Gorochov G. Intestinal Candida albicans overgrowth in IgA deficiency. J Allergy Clin Immunol. 2023 Sep;152(3):748-759.e3. doi: 10.1016/j.jaci.2023.03.033. Epub 2023 May 9. PMID: 37169153.

Pietrzak, B., Tomela, K., Olejnik-Schmidt, A., Mackiewicz, A., & Schmidt, M. (2020). Secretory IgA in Intestinal Mucosal Secretions as an Adaptive Barrier against Microbial Cells. International journal of molecular sciences, 21(23), 9254. https://doi.org/10.3390/ijms21239254