We are starting to learn how the gut can influence the way we feel and behave. In this blog, we look into some of the latest research into how the gut, and the bacteria it contains, is playing a role in our health.

Dr Beckie Port
Sep 10, 2018 · 8 min read

When was the last time you had butterflies in your stomach? Perhaps it was when you had to deliver that big presentation, or maybe it was in anticipation of a celebration or special event. When we are excited or anxious about something, it does feel like the brain is sending messages to the stomach. But what if the stomach is also sending messages to your brain?

Most people will associate neurons with the brain and possibly the brain stem. But 70% of all neurons in our bodies outside this central nervous system are in the intestines — or gut — the organs responsible for digesting food. And it turns out that the stomach and brain are sending signals to each other back and forth along the vagus nerve that directly connects the guts nervous system to the central nervous system.

It is through this connection that the gut can influence a myriad of different physiological and psychological responses — from inflammation to digestion, mood to anxiety. But it’s not us that is necessarily in control of the signals that our gut is sending, instead it is the billions of microscopic organisms that live in our gut which make up what is known as the gut microbiota.

Established within the first few years of our lives, the average person has up to 2kg of microbes living in their gut helping to digest their food, make vitamins and fight bad bacteria and infection. And while there are fungi, viruses and other microscopic and single celled organisms living in the gut, it is the bacteria that we know most about.

Our gut bacteria interact with the rest of the body by releasing chemicals. The vagus nerve, with its ability to sense these chemicals, then sends information from the gut into our central nervous system where it influences our unconscious or otherwise involuntary behaviours.

In most people, the microbiota is fairly stable although the composition of microbes can change over time or as overall health changes. We also know that a number of factors — including chronic inflammation, stress, antibiotics, high carbohydrate or sugar diets — can alter our gut balance, and with a direct connection to our brain, they could do more than leave you with an upset stomach.

Targeting the gut to improve health

Over the last decade, researchers have become interested in how maintaining the levels of certain types of bacteria may help promote general health and wellbeing. And a quick search of the internet will show up a number of diet and supplement plans that promise to improve health from the inside out, altering the hormones the gut produces to tackle a range of health conditions from autoimmune diseases to chronic fatigue. So, does research really support the saying ‘healthy gut, healthy you’? And how about these so called gut friendly recommendations, such as eating easily digestible foods and gut promoting natural herbs or probiotics, taking time to relax, and increasing the amount of fibre in the diet?

The evidence supporting the benefits of probiotics use for general health is far from conclusive, but there is evidence that even short-term exposure to stress can impact on the community of microorganisms living in the gut, so there may be something in taking time to look after your mental health to keep your gut happy. However, it is diet that is the main contributor to the changes in the microbiota. Certain diets, including high fibre diets, have been linked to potential gut related benefits, such as the promotion of potentially beneficial bacteria by a Mediterranean diet, or the inhibition of pathogenic bacteria such as E.coli in vegetarians. But not all diets may be beneficial as some research suggest gluten free diets can actually increase E.coli levels, and decrease potentially beneficial bacteria levels. What is clear is there is still much to learn when it comes to how to look after our gut and how much this may impact on our general health.

More recently research has focused on a number of conditions that appear to be linked to our gut health with the aim to develop new treatment strategies. Conditions where the guts appears to play a role are numerous and varied, and include obesity, diabetes, cancer, depression and even neurodegenerative conditions such as Parkinson’s and Alzheimer's. Indeed, perhaps it is through encouraging the growth of a healthy community of micro-organisms that smoking and drinking coffee are able to reduce the risk of Parkinson’s. But as well as these potential protective effects, could negative changes in the gut actually lead to the loss of brain cells?

The start of neurodegeneration

Many people with Parkinson’s notice changes in their digestion, which can impact on quality of life as well as the effectiveness of medications that people rely on. Now researchers are coming to the conclusion that changes in the gut may be more than just a symptom. And, despite being a brain condition, evidence is mounting that some of the earliest changes that lead to Parkinson’s may actually start in the gut.

Researchers have discovered sticky clumps of a protein called alpha-synuclein, which is believed to play a role in the progression of Parkinson’s, in the guts of those in the early stages of the condition. And other studies have found similar clumps in the vagus nerve, further supporting the idea that the clumps may not originate in the brain.

Additional evidence of the involvement of the gut in Parkinson’s comes from a procedure for the treatment of ulcers that involved cutting the information flow between the gut the brain by severing the vagus nerve. The technique was common in the 1970s and 80s, and has since been linked to a reduced risk of Parkinson’s suggesting it may have also inadvertently stopped alpha synuclein clumps making the journey from the gut to the brain, and ultimately causing the loss of brain cells.

These findings have caused researchers to rethink where Parkinson’s actually starts. It could mean, for some, the condition may start in the gut, or somewhere else in the body, and travel up the vagus nerve towards areas of the brain affected in Parkinson’s — a theory which has recently gained support from a research team in Alabama, at least in a mouse model of the condition.

Perhaps most surprising are results from research looking into the effect of removing bacteria from the gut on susceptibility to disease. Researchers in California discovered that mice raised in a germ-free environment, who were not given the chance to develop a normal complex range of micro-organisms living in their gut, may be protected from Parkinson’s. They also found that bacteria taken from people with Parkinson’s could worsen motor symptoms suggesting that the altered make up of gut microbiota in Parkinson’s may actually affect the progression of the condition.

Similar findings have been show in other conditions with research showing germ free mice can eat more and gain less weight, and gut bacteria playing a role in the development of Alzheimer’s and even the progression of cancer.

While this research gives key insights into the causes of disease, it also feeds into wider considerations about how lifestyle and environment factors that influence our gut microbiota may alter our risk of developing certain conditions.

Differentiating the good from the bad

One avenue to tackling neurodegenerative conditions, and indeed other conditions liked to the micro-organisms living inside us, may be to target harmful gut bacteria with antibiotics. Indeed, the researchers in California showed using antibiotics produced the same protective effects as raising mice in a germ-free environment.

It’s an exciting prospect that simple antibiotics could provide us with an opportunity to develop treatments that can intervene before neurological conditions even start. However, up to a trillion microbes live in our gut. Many are beneficial and it’s worth noting that using current antibiotics, which wipe out both good and bad bacteria indiscriminately, in the long-term or at high-doses can have significant health risks — not to mention the risks of antimicrobial resistance.

We know that not all bacteria are equal. Some, such as E.coli and H. pylori, can cause stomach infections, while others are marketed in probiotic yogurts as good for us. But overall, we don’t know enough to differentiate between them, and we certainly don’t understand which bacteria are linked to different conditions. But if we did, perhaps we could pinpoint those that are harmful and develop antibiotics that target the damaging bacteria while leaving the beneficial ones unharmed, or treatments that help the best bacteria flourish.

It sounds simple, and understanding the effects of different bacteria could form the basis of a new treatments, but when you consider there are hundreds of different species in the gut it becomes a little harder to figure out which bacteria are good, bad or somewhere in the middle.

Fortunately there are researchers unpicking this problem — people like Dr Doitsidou and her team who are systematically studying the various types of bacteria to identify those key few that play an important role in Parkinson’s.

The team is using a microscopic and transparent type of C. elegans worm to study the effects of individual types of bacteria on the brain cells affected in Parkinson’s. These worms happily eat bacteria, so the researchers simply need to feed a different type of bacteria to each group of worms. The worms also have a super power — they have been engineered so that the nerve cells the team are interested in glow green under the microscope.

From the hundreds of bacteria that may play a role, the team hope to identify the key ones to look at in more detail. They will then try to discover the mechanisms by which these bacteria have either protective or damaging properties, knowledge which could also lead to new treatments.

It’s early days as scientists are only just starting to learn about how the gut may be linked to conditions like Parkinson’s, but this project will give us invaluable insight and potentially lead to new treatments. And while there will still be many questions to answer, the hope is that research projects like this that aim to better understand the gut will be key to treating many health conditions.


Parkinson’s is a progressive neurological condition that affects about 145,000 people in the UK and an estimated 7–14 millions people worldwide. There is no currently no cure, and we desperately need better treatments.

You can help us speed up the development of new and better treatments, and a cure for Parkinson’s by donating to this project today.

Parkinson’s UK

Get the latest research news, discover more about Parkinson’s and read about how others are getting involved. For information and support, visit www.parkinsons.org.uk

Dr Beckie Port

Written by

Research Communications Manager at @ParkinsonsUK. Ex-researcher in oncology and virology.

Parkinson’s UK

Get the latest research news, discover more about Parkinson’s and read about how others are getting involved. For information and support, visit www.parkinsons.org.uk

Welcome to a place where words matter. On Medium, smart voices and original ideas take center stage - with no ads in sight. Watch
Follow all the topics you care about, and we’ll deliver the best stories for you to your homepage and inbox. Explore
Get unlimited access to the best stories on Medium — and support writers while you’re at it. Just $5/month. Upgrade