Brain and Nerves

How the Gut Communicates With the Nervous System

The gut has its own nervous system, containing more nerve cells than the spinal cord. It connects to the brain through the vagus nerve, through hormones, through immune signalling and through compounds bacteria release into the blood. That gives several separate routes rather than one, which is why the conditions on this page involve genuinely different mechanisms. Some concern nerve pathways carrying something physically from gut to brain. Others concern compounds bacteria produce. Others concern nutrients bacteria compete for.

Four different routes, four kinds of evidence

The first route is physical. In Parkinson's disease, constipation frequently appears decades before the first tremor, and researchers have traced the nerve pathway a misfolded gut protein takes on its way to the brain.

The second is chemical, and the clearest demonstration concerns epilepsy. Nearly a third of the 50 million people with epilepsy worldwide don't respond to medication alone, and the ketogenic diet has long been used for some of them. Researchers then showed that the diet's anti-seizure effect is mediated by gut bacteria. Remove the bacteria and the diet stops working.

The third is immune. One study compared 576 people with multiple sclerosis against healthy members of their own households. That design controls for shared diet and environment. It found specific bacterial differences linked to both disease risk and severity.

The fourth is competition for nutrients. Up to 40% of people on long-term metformin develop vitamin B12 deficiency. Researchers identified a specific gut bacterium that hoards the vitamin for itself, which offers an explanation for the nerve damage that can follow.

Symptoms without a clear diagnosis fit here too. Brain fog was found alongside small intestinal bacterial overgrowth in 68% of affected people, against 28% of similar patients without the symptom, and it improved when the overgrowth was treated.

Source: The Gut Microbiota Mediates the Anti-Seizure Effects of the Ketogenic Diet

Source: Gut microbiome of multiple sclerosis patients and paired household healthy controls reveal associations with disease risk and course

Source: Brain fogginess, gas and bloating: a link between small intestinal bacterial overgrowth, probiotics and metabolic acidosis

What this means for you

New or worsening neurological symptoms, including tremor, numbness, weakness or memory change, need proper medical assessment, since diagnosis determines treatment and several causes are reversible. In addition, the research above shows a diet used for epilepsy working through gut bacteria rather than around them, bacterial differences in multiple sclerosis holding up against household controls, and a gut bacterium competing for the vitamin whose deficiency causes nerve damage. A varied, plant-rich diet supports the same gut bacteria this research ties to steadier signalling along these routes. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.

Explore brain and nerve topics on this page

The panels on this page cover conditions connected to the gut by genuinely different mechanisms, so it's worth reading them separately rather than as one story.

Parkinson's disease, Alzheimer's disease, dementia and multiple sclerosis concern long-term degeneration and immune involvement. Epilepsy is where a dietary treatment was shown to work through bacteria.

Migraine, headaches and nerve pain concern how pain signals are generated and amplified. Brain fog, memory problems and long COVID concern symptoms that are real but hard to measure. Neuropathy concerns nutrients bacteria compete for.

Use the panels on this page to find the one relevant to you.