The key to a healthy brain may lie in your gut

Since the early 2000s, understanding of the gut’s role in a broad range of health conditions has advanced dramatically. Photo / Tyrone Blight-Avery, Unsplash

Jeremy Diskin initially attributed the stiffness in his arms to a football injury. Aged 55, he was still playing the game, and hoped physiotherapy would resolve what he assumed was a sports-related complaint. But it didn’t seem to be working, and it wasn’t just his arms: he also had stiff shoulders, a tight neck and difficulties with mobility. “I went for a scan and that showed nothing at all, so the consultant said, ‘I hate to say this but I wonder if it could be Parkinson’s’,” he recalls.

The doctor’s hunch was correct. Since Diskin’s diagnosis in 2015, the property manager from Sheffield has experienced increased difficulty walking and struggles to stay asleep at night. His fine motor skills have become impaired, meaning tasks like tying a shoelace can prove challenging. But when Diskin took part in a medical trial that set out to investigate whether taking a probiotic could, in changing the gut microbiome, improve Parkinson’s symptoms, he started to feel “a bit better”.

This might sound surprising. Why should the trillions of bacteria, fungi and other microbes in our gut, which make up what is known as the gut microbiome, have anything to do with a neurodegenerative disease like Parkinson’s? That is what scientists have lately been trying to establish – and it’s been suggested we could now be at the dawn of a golden age for gut-health science.

As little as 25 years ago, the idea of searching in the gut for answers to a host of seemingly unrelated physical and mental-health issues might have struck many as absurd. How could these microbes have anything to do with, say, depression, the immune system or disorders of the brain? Yet since the early 2000s, understanding of the gut’s role in a broad range of health conditions has advanced dramatically, after scientists worked out how to sequence DNA from the gut microbiome. Recent research indicates that understanding the gut could even help us unravel the mysteries of the two most common neurodegenerative diseases, Parkinson’s and Alzheimer’s, cures for which have so far proved elusive.

In the popular imagination, sufferers of Parkinson’s are characterised primarily by their involuntary shaking. We do not tend to associate the condition with digestive symptoms, but they have been linked for a long time. When the British surgeon James Parkinson first identified what he called the “shaking palsy” more than 200 years ago, he noted some patients also suffered from constipation. But, says neuroscientist Dr Lynne Barker, who carried out the trial Diskin participated in, the association between Parkinson’s and gut problems has been pushed to one side. “There’s been very little focus on what’s happening in the rest of the body and why [patients] have such problems with bloating, constipation and vomiting.”

Now, scientists are starting to pay more attention to these links. Recent studies show the composition of the gut bacteria is different in people with brain diseases like Parkinson’s and Alzheimer’s from that of non-sufferers. The guts of people with these illnesses have been found to contain slightly more of the bacteria that increase inflammation and less of the sort that decrease it.

In 2016, researchers found probiotics in yoghurt and supplements could help improve cognition and memory in those with Alzheimer’s disease. Photo / Nastya Dulhiier, Unsplash

During the summer, Dr Barker presented to the British Dietetic Association some of her latest findings on the role of the microbiome and the gut-brain axis in health and disease and potential therapeutic approaches. She and colleagues at the Centre for Behavioural Science and Applied Psychology at Sheffield Hallam University, alongside collaborators from elsewhere, had studied the species of bacteria present in the gut of 26 Parkinson’s patients and found about 100 key species that were present in all of them. These, says Dr Barker, could be described as a “Parkinson’s signature”. Of the gut bacteria associated with Parkinson’s, about half were found to be “bad”, or what Dr Barker describes as potentially detrimental. “That’s giving us clear evidence this is not a healthy microbiome,” she says.

She and her colleagues administered a liquid probiotic formulation containing four bacterial strains (Lactobacillus casei, acidophilus and plantarum as well as Enterococcus faecium) to 14 of the patients in their study, including Diskin, and a placebo to the other 12. When they examined the gut bacteria of the patients again after 12 weeks, they found the so-called good species had increased in those who had taken the probiotic, while the bad species had declined. The same result was not observed in the placebo group.

“What we’ve got is a change in the composition of the signature,” says Dr Barker. “We’ve got good microbes increasing in prevalence and the detrimental ones decreasing in prevalence.”

Diskin doesn’t want to overstate the difference it made to him, but says: “I probably walked a bit better [while taking the probiotic]. Movement was a bit easier. It was a positive experience overall.”

So, can changing the gut microbiome actually make a difference to the symptoms of Parkinson’s, or indeed other brain diseases? “Potentially,” says Dr Barker, adding that some of those who received the probiotic found their constipation eased. “They were eulogising about it and saying, ‘I felt so good on that, I’ve been able to go to the toilet.’ Our hypothesis is we expect to see some relationship between what’s happening with the [gut] microbes and the patient’s symptoms. You can build on that with the medication they’ll be absorbing. If the gut’s working properly, everything else will follow.”

Other research points in a similar direction. Many studies have revealed a link between intestinal disorders and Parkinson’s disease. In 2016, researchers at the California Institute of Technology conducted a study in which they transplanted microbes from the faeces of Parkinson’s patients into the guts of mice. They observed that these mice showed greater movement dysfunction than others that were given bacteria from humans without Parkinson’s. The findings seemed to suggest that certain gut bacteria could contribute to difficulties with movement in Parkinson’s patients.

The role of probiotics in altering the gut bacteria and thus potentially improving the symptoms of neurodegenerative illnesses has also been explored before. In 2016, researchers at Kashan University of Medical Sciences and Islamic Azad University in Iran found probiotics found in yoghurt and supplements could help improve cognition and memory in those with Alzheimer’s disease. Other studies have produced similar results.

The next stage is working out the link between what’s happening in the gut and what’s happening in the brain. What is cause and what is effect? Is the nature of the gut microbiome driving the neurodegenerative symptoms, or vice versa?

Eating a high-fibre high Mediterranean-style diet helps to maintain a healthy gut microbiome. Photo / Edgar Castrejon, Unsplash

“We know the brain and the gut communicate constantly,” says Dr Siobhain O’Mahony, an investigator at APC Microbiome Ireland and senior lecturer in the Department of Anatomy and Neuroscience at University College Cork. “The bacteria are key to these communications. There’s a suggestion that a dysfunctional bowel leads to changes in the major protein associated with Parkinson’s, called alpha synuclein, which could travel through the spinal cord or the vagus nerve to the brain.”

Before motor dysfunction is noted in Parkinson’s sufferers, studies have shown the alpha synuclein protein is present in the gut. Research has also shown that cutting off the vagus nerve, which transmits information to and from the brain to tissues and organs in other parts of the body, can in fact reduce the risk of Parkinson’s.

“The vagus nerve is a major [line of] communication between brain and bowel,” says O’Mahony. It is part of what Dr Barker calls the “biological pathway” of the gut-brain axis. “Different organs can communicate through the vagus nerve to the brain,” she says. “For instance, that’s how the brain knows the stomach is full.”

It is thought it could also be the pathway that allows an unhealthy gut microbiome to affect the workings of the brain. But more research on the precise nature of the relationship between the microbes in the gut and activity in the brain is needed. “At the moment, we don’t know if changes to the gut microbiome are an effect of the [neurodegenerative] disease or are driving the disease,” says Dr Susan Kohlhaas of Alzheimer’s Research UK.

Dr O’Mahony suggests the communication between the gut and brain is bidirectional. “It’s not defined where the actual disease starts and there are probably subsets of individuals where it starts in the gut and subsets where it starts in the brain,” she says. “That’s what’s really confusing. There’s the possibility of the origins of the disease in both these end organs.”

Parkinson’s is thought to affect about one in 500 people while Alzheimer’s, the most common cause of dementia in the UK, affects an estimated one in 14 over-65s and one in six over-80s. The pressing question is where these latest findings about the gut-brain axis leave us when it comes to finding better treatments and potentially even cures or means of prevention.

Dr Kohlhaas takes a cautiously optimistic approach. Alzheimer’s, she points out, is a complex condition and untangling the processes that drive it will require a concerted effort. It is already known that up to 40 per cent of the risk factors for the disease are environmental, and that maintaining a healthy diet is one way to help stave it off. What is better established is that to maintain a healthy gut – and thereby reduce the risk of a whole host of illnesses – we need plenty of fibre in our diets.

Dr Barker recommends that, in addition to eating plenty of vegetables and roughage, we consider taking good prebiotics and probiotics. She advises we carefully research them, though, to ensure we’re taking those that are actually effective.

Meanwhile, she is hopeful the gut microbiome could ultimately be the answer to the prayers of not just scientists but millions of families affected by a whole host of brain conditions and disorders, ranging from the brain fog associated with long Covid to autism. “It could potentially lead to a way of managing not just Parkinson’s but everything,” she says.

Five things you can do for a healthier gut microbiome

• Eat a high-fibre high Mediterranean-style diet.
• Try fermented products, such as yoghurt, miso, sauerkraut, kimchi and tempeh.
• Consider taking probiotics and prebiotics to help healthy bacteria grow in the gut.
• Keep windows open when possible. This will help reduce the bad microbes you’re breathing in.
• Regular exercise has a beneficial effect on the microbiome and brain.

Source: Dr Lynne Barker, Sheffield Hallam University