When IBS Isn’t About Food: The Science of Stress, Survival, and Gut Dysfunction

Flying through a category 5 cyclone is not an experience I recommend. Ryanair were kind enough to let me have that experience a couple of weeks ago (they will be hearing from me): Four aborted landings. Severe turbulence. A cabin full of silent, then screaming, braced bodies. And the very real, visceral sense that something was not right. For most people, that’s a story about fear. For me—someone with a long-standing diagnosis of irritable bowel syndrome (IBS) - largely in remission —it became a physiological experiment in real time (I obviously wasn't thinking that at the time!).

Within hours of landing in a rain-lashed Athens, my gut responded exactly as the literature predicts:a full-scale IBS flare. No dietary indiscretion. No change in routine. No microbiome “trigger food.”

Just one variable: acute, sustained threat perception.

IBS Is Not Just a Gut Condition

As clinicians, we often begin with food. And rightly so. Dietary triggers, fermentable carbohydrates, fibre modulation, and microbiome composition all play critical roles in IBS pathophysiology. But this framework is incomplete if we ignore one of the most robustly supported mechanisms in IBS research: disordered gut–brain signalling

IBS is now widely understood as a disorder of gut–brain interaction (DGBI)—a term formalised in the Rome IV criteria.

This includes:

• Visceral hypersensitivity (heightened pain perception in the gut)

• Altered motility (accelerated or delayed transit)

• Central nervous system dysregulation

• Autonomic imbalance

And crucially: increased responsiveness to stress

What Happened in My Body (According to Science)

During that flight, my body did exactly what it is evolutionarily designed to do. The perceived threat activated the hypothalamic–pituitary–adrenal (HPA) axis and the sympathetic nervous system:

• Corticotropin-releasing hormone (CRH) was released

• Cortisol levels rose

• Sympathetic (“fight or flight”) output increased.

My heart was pounding at the same rate, for the one and a half hours we were in the cyclone, as when I am jogging.

This cascade has direct, measurable effects on the gut:

1. Increased intestinal permeability

CRH has been shown to disrupt tight junction integrity, contributing to the so-called “leaky gut” phenomenon.

2. Altered motility

Stress can accelerate small bowel and colonic transit—clinically presenting as urgency or diarrhoea (the toilet wasn't fun once I got there)

3. Visceral hypersensitivity

The brain amplifies pain signalling from the gut, lowering the threshold for discomfort.

4. Mast cell activation

Stress-related signalling can activate mucosal mast cells, increasing histamine and inflammatory mediators—strongly implicated in IBS symptoms.

In short: My gut behaved as though it was under attack—because my brain told it it was.

The Gut–Brain Axis: Not a Metaphor, but a Network

The gut and brain are in constant bidirectional communication via:

• The vagus nerve

• The enteric nervous system

• The immune system

• The endocrine system

  
  

This is not abstract—it is anatomical, biochemical, and measurable. When the brain perceives danger, gut function is deprioritised. Digestion is not essential for immediate survival. Instead, the body shifts resources toward:

• vigilance

• rapid energy mobilisation

• threat response

For individuals with IBS, this system is often sensitised, meaning the gut response is exaggerated and prolonged.

Why Diet Wasn’t the Issue

One of the most important clinical reflections from this episode:

I did not change my diet—and I did not need to.

The trigger was not fermentable carbohydrates or fibre imbalance. It was acute nervous system dysregulation. This matters, because many patients are led to believe that every flare is food-related.

But in reality:

• Some flares are neurogenic

• Some are circadian

• Some are immune-mediated

• And many are multifactorial

  
  

Over-restricting diet in response to every flare can worsen long-term outcomes, particularly via reduced microbial diversity.

Regulating the Nervous System: Evidence-Based Approaches

Once the acute stressor passed, my focus shifted—not to food—but to restoring autonomic balance.

Here’s what that looks like in practice, grounded in physiology:

1. Circadian Rhythm and Gastrointestinal Function

The gastrointestinal tract follows a circadian pattern, regulated by peripheral clocks influenced by the central suprachiasmatic nucleus.

Disruption affects:

• gastric emptying

• colonic motility

• hormone release (e.g. cortisol, melatonin)

Clinical evidence shows that circadian misalignment is associated with worsened IBS symptoms.

Practical application:

• Regular sleep–wake timing

• Consistent meal timing

• Minimising late-night eating

This supports synchronisation of gut motility and hormonal signalling.

2. Breathwork and Vagal Tone

Slow, diaphragmatic breathing has been shown to:

• Increase vagal tone

• Reduce sympathetic activation

• Improve heart rate variability (HRV)

This directly influences the gut via the vagus nerve, which modulates:

• motility

• inflammation

• visceral sensitivity

Techniques:

• Diaphragmatic breathing (≈6 breaths per minute)

• Box breathing

  
  

  These are not “wellness trends”—they are neurophysiological interventions.

  
  

3. Movement and Motility

Gentle physical activity:

• Reduces cortisol

• Enhances parasympathetic activity

• Supports gastrointestinal transit

  
  

Importantly, intensity matters:

• High-intensity exercise can exacerbate symptoms during flares

• Low-intensity, rhythmic movement is regulatory

  
  

4. Sensory Grounding and Threat Reduction

From a neurobiological perspective, grounding techniques:

• Reduce amygdala activation

• Increase prefrontal cortex engagement

• Signal safety to the nervous system

  
  

This shifts the body out of a defensive state.

5. Progressive Muscle Relaxation

Chronic low-grade muscular tension feeds into central sensitisation.

Progressive relaxation:

• Reduces somatic tension

• Decreases sympathetic tone

• Improves perception of internal signals (interoception)

Working With, Not Against, the “Primitive Brain”

What I often call the “animal brain” is more precisely the limbic system and brainstem survival circuitry.

It is:

• fast

• unconscious

• protective

During the cyclone, this system did its job perfectly. The goal is not to suppress it—but to reassure it.

This is where many IBS management strategies fall short:they address the gut, but not the perceived threat state driving the gut response.

Final Thoughts

This experience was a powerful reminder—both personally and professionally—that: IBS is not just a disorder of digestion. It is a disorder of regulation. Food matters. The microbiome matters.

But so do:

• stress physiology

• circadian biology

• autonomic balance

If we ignore these, we miss a large part of the clinical picture.

And sometimes, the most effective intervention is not removing another food—

—but helping the body remember that it is safe again. I have never, ever been so happy to back on earth among the spring flowers! And the flare is over too :-)