The Gut-Brain Axis

How your mental health and nervous system may be contributing to your gut issues

We often hear about how the gut can impact the brain but the relationship runs both ways. Mental health is now recognised as a key contributing driver in many cases of IBS subtypes and functional dyspepsia. This has given rise to the field of neurogastroenterology, which explores the gut-brain axis in clinical depth, and to a formalised diagnostic framework for disorders of gut-brain interaction (Rome IV, 2016).

"The gut-brain axis (GBA) consists of bidirectional communication between the central and the enteric nervous system, linking emotional and cognitive centers of the brain with peripheral intestinal functions" ~ (Carabotti et al., 2015).

(Carabotti et al., 2015)

How the brain and nervous system can impact your gut

1. Pain perception For some people, the way pain signals are processed between the gut and the brain becomes dysregulated, a phenomenon known as visceral hypersensitivity. The nervous system loses its ability to appropriately downregulate pain, leading to heightened and persistent discomfort. Both neuromodulator therapies and behavioural interventions (such as gut-directed hypnotherapy and CBT) have demonstrated efficacy in resetting this system and reducing symptoms.

(Rome, 2021)

2. Motility The autonomic nervous system directly regulates gut motility. When autonomic function is disrupted, digestion can slow or accelerate, contributing to symptoms such as constipation, diarrhoea, or bloating. Research in neurological injury models, including traumatic brain injury, demonstrates that neuroinflammation can impair autonomic control and significantly disrupt motility patterns (Hanscom et al., 2021), illustrating how upstream nervous system dysfunction translates to downstream gut consequences.

3. Gut immune function and intestinal barrier integrity nervous system imbalance via the autonomic system or the HPA axis, commonly associated with chronic, unmanaged stress,  can impact gut immune function and promote a pro-inflammatory state. Evidence indicates this increases vulnerability to intestinal barrier permeability, a mechanism that may underlie stress-related flares in gut symptoms (Leigh et al., 2023).

4. Microbiome composition Emerging evidence from observational and animal studies suggests that chronic stress can alter gut microbiome composition, though robust human RCT data in this area remains limited (Leigh et al., 2023). This is an active area of research with clinical relevance that warrants monitoring. 

The Autonomic Organisation of The Gut (Leigh et al., 2023)

Because the gut-brain relationship is bidirectional, the downstream gut changes described above can in turn further dysregulate nervous system function, creating a reinforcing cycle that can be difficult to break without addressing both systems holistically.

If you notice that stress reliably worsens your digestive symptoms, nervous system support should be part of your gut health plan.

Here are some things to consider for nervous system support that supports gut health…

1. Protect your sleep: sleep is the primary period of nervous system repair and regulation.

2. Move your body:  regular exercise supports autonomic balance and reduces stress reactivity.

3. Build sustainable stress management strategies:  this looks different for everyone - the goal is not to remove stress but rather ensure you can manage it constructively and recover. There is a lot of evidence based tools that you can be supported with including: mindfulness, CBT, hypnotherapy, counselling, etc. 

4. Slow down at mealtimes: This is HUGELY underrated and yet so important.  Sitting down, taking a few slow breaths before eating, and chewing thoroughly helps shift your nervous system into parasympathetic ('rest and digest') dominance, which is the optimal state for digestion.

5. Prioritise nutrient-dense wholefoods: Key nutrients including B vitamins, zinc, magnesium, and omega-3 fatty acids are essential precursors for neurotransmitter synthesis and neurological resilience, which in turn supports gut-brain signalling.

6. Address underlying anxiety or depression:  If these are present, they are likely bidirectionally reinforcing gut symptoms. Seek appropriate support. 

Supporting gut health can also positively feedback to the brain and nervous system. For more on targeted gut support, see post on fibre, prebiotics and polyphenols and find some more practical gut health foundations here. If symptoms persist, personalised clinical assessment is recommended as the mechanisms above interact differently in each person.

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