Parkinsons & the gut-brain-axis

A growing body of evidence is turning the Parkinson’s paradigm on its head.

We’ve long assumed it starts in the brain. But what if it actually starts in the gut?

A major meta-analysis published in 2020 has confirmed what many functional practitioners have suspected for years: gut dysbiosis is a consistent and global feature of Parkinson’s disease (PD).

Let’s break it down.

Researchers analysed gut microbiota from:

• 223 Japanese PD patients and 137 controls
   
• Four additional datasets from Finland, Russia, the USA, and Germany
   

They adjusted for confounders like age, sex, constipation, BMI, and Parkinson’s medications.

Then they meta-analysed all five datasets.

The results were striking.

Across all five countries, the same pattern kept showing up:

✅ Akkermansia (a mucin-degrading bacterium) was increased
❌ Faecalibacterium and Roseburia (butyrate-producing, anti-inflammatory bacteria) were decreased

These changes weren’t due to medications or constipation. They were seen even after adjusting for those variables.

This is no coincidence.

Akkermansia breaks down the gut’s protective mucus layer.

This increases intestinal permeability—often referred to as “leaky gut”.

Once that barrier is compromised, the enteric nervous system is exposed to inflammatory triggers, pesticides, and oxidative stress. This can lead to the misfolding and aggregation of α-synuclein proteins—the hallmark of Parkinson’s pathology.

At the same time, the loss of butyrate-producing bacteria like Faecalibacterium and Roseburia means lower levels of short-chain fatty acids (SCFAs). These SCFAs normally suppress neuroinflammation and support the blood–brain barrier.

The net result?

A gut primed for inflammation. A nervous system vulnerable to attack. And a brain that bears the consequences.

• PD severity correlated with higher Akkermansia and lower Faecalibacterium/Roseburia
   
• PD patients had changes in metabolic pathways, particularly butanoate and propionate metabolism—suggesting altered SCFA dynamics
   
• Certain medications (like COMT inhibitors) were found to significantly distort microbiome readings—something most studies fail to control for
   
• Constipation, often seen decades before PD diagnosis, also impacts the microbiome, but isn’t the root cause - it's a sign of underlying imbalance.
   

Parkinson’s is not just a brain disease.

It’s a gut-brain disease—with early signs appearing in the gut microbiome years before motor symptoms begin.

If you’re still only looking at Parkinson’s through a neurological lens, you could be missing the root cause.

 Nishiwaki, H., Ito, M., Ishida, T., Hamaguchi, T., Maeda, T., Kashihara, K., ... & Ohno, K. (2020). Meta-Analysis of Gut Dysbiosis in Parkinson's Disease. Movement Disorders, 35(9), 1626-1635. https://doi.org/10.1002/mds.28119