The Gut-Brain Axis and a Massive Thank You!

A massive thank-you from me; then, discover how to use the gut-brain axis to improve your health.

May 13, 2024

Hey Brainiacs,

Welcome to this week's newsletter! Let’s explore how our gut and brain communicate with each other, and how we can exploit this connection to help us feel our best.

But First…

A massive thank you to everyone who came on Tuesday, both in-person and online! I am overwhelmed with emotions at the sight of such a large turnout. It means so much to me to see the support and love out there for Rewire. And a big thank you to @seedtalks for hosting me! Please check them out for future talks, they are one of the best in the UK for mind-expanding talks across the country.

@NicolesNeuroscience signing books and taking photos. — Thank you to everyone who came on Tuesday, it was incredible to see so much support! And thank you @fosterstudios for the amazing photos!

Thank you also to everyone who has supported me by buying the book - WE GOT TO NUMBER 1 ON AMAZON! I genuinely could tear up just thinking about this- and it wouldn’t be possible with you guys, so thank you.

If you haven’t bought the book yet, I still love and appreciate you, but if you do want to buy it, you’ll be helping me to get on the Sunday Times bestseller list and spread the power of neuroscience! It would mean loads to me.

Buy Rewire Here!

Now, onto some more science…

The Gut-Brain Axis

The gut-brain axis is a system of bidirectional communication between our gastrointestinal tract and our central nervous system (brain and spinal cord)^1,2. This means that the brain can talk to the gut, sending signals to encourage digestion (rest and digest) or to stop and prioritize other mechanisms (fight or flight), and the gut can talk to the brain, influencing mood, cognition, sleep, and eating habits^3,4!

The brain and gut are connected through physical connections, like the vagus nerve⁵, and biochemical connections, like the neurotransmitters^6,7 and short-chain fatty⁸ acids released by gut microbes. Gut microbes are the micro-organisms, such as bacteria, fungi, and viruses, that live in our digestive tract. Microbes in our gut actually outnumber our cells⁹, so the products they release are extremely important!

The Vagus Nerve

The vagus nerve is one of the biggest nerves connecting our brain and gut. 80% of this nerve is dedicated to sending signals towards the brain, and 20% is dedicated to sending signals to the gut¹⁰. Importantly, the vagus nerve can sense the metabolites released by microbes and send this information to the brain, so it can respond accordingly¹⁰. In fact, the beneficial emotional effects of taking probiotics is lost if the vagus nerve is cut¹¹.

But how does the vagus nerve produce these beneficial effects in the first place? Well, we know that stimulation of vagal fibers running towards the brain influences monoaminergic (like dopamine, noradrenaline and serotonin) brain systems, which are important for mood and anxiety⁵. We also know that stimulation of the vagal nerve leads to an anti-inflammatory pathway, inhibiting the production of inflammation messengers (cytokines) and reducing intestine permeability. And we know that stress inhibits the vagus nerve, explaining why chronic stress can lead to a lowered immune system, increased illness, and increased gut problems¹⁰.

Onto The Microbes

Microbes are incredibly important because they release metabolites which have calming and feel-good effects, like serotonin and GABA^6,7. We know these metabolites do have effects on the brain because probiotics influence emotional behavior and GABA receptor expression in animal studies¹¹. Microbes also release molecules called short-chain fatty acids, which are important in appetite¹², the blood-brain barrier¹³, and in feeding your gut cells⁸! However, microbes are also really important in disease because ‘bad’ microbes can release toxic factors, such as LPS, which encourage inflammation¹⁴. And we know that gut inflammation is linked to stress-related psychiatric disorders¹⁵.

So now we know how the brain and gut can interact, but let's dive a little deeper into what commonly goes wrong into this interaction. Then, I’ll give you some tips to help shift the balance from a dysfunctional microbiome to a functional one!

The Microbiota in Mental Health

There is a balance to everything in life, and the gut microbiota is no exception to that. Too many of one type of bacteria can be a bad thing. In fact, there is now a pile of evidence showing that the gut microbiota is disrupted in many mental disorders. Patients with generalised anxiety disorder (GAD) had less short chain fatty acid (SCFA)-producing bacteria and less microbial diversity than populations without GAD¹⁶. Similarly, patients with depression have less SCFA-producing bacteria, less diversity in their microbial environment, and less Bifido- and Lacto- species¹⁷. In fact, a recent meta-analysis (a study looking at lots of other studies, essentially) found that probiotics were an effective treatment for major depressive disorder when used as a supportive therapy or on their own¹⁸. Additionally, we know that vagal nerve stimulation can be a good therapy for patients with treatment-resistant depression, although the mechanisms of why is not totally clear¹⁹.

The Microbiota and Gut Disorders

We know there is less diversity of gut microbes and reduced stability of gut microbes in those suffering from IBS²⁰. Additionally, a lower vagal tone is found in patients with IBD and IBS, potentially explaining why inflammation runs so rampant in those gut disorders^5,10. Many clinical trials that have tested probiotics as a treatment for IBS and IBD have found success, with people reporting less pain and discomfort and almost all symptoms improved²¹. I think it is important to highlight the positive impact of probiotics and a balanced gut microbiome on gut disorders, because these disorders are closely linked with mental health²².

What can we do to improve our gut microbiome and promote a healthy relationship between our brain and gut?

Top Tips

1. Eat fermented foods, like yogurt! Fermenting food encourages the growth of pre-existing probiotics, and fermented foods are associated with lower rates of depression²³.

2. Eat your fruit and veggies. Fruits and vegetables (particularly whole grains such as quinoa, brown rice, sunchokes, artichokes, chicory, endive, bananas and apples) contain soluble fibre, galactooligosaccharides (GOS), and fructooligosaccharides (FOS), which are natural prebiotics for helpful bacteria^24,25.

3. Increase diet diversity and reduce intake of fatty foods. Eating a Norwegian-style diet, rich in fish, eggs, nuts, and poultry, is associated with lower levels of depression and anxiety than eating a western-style diet, rich in fatty foods²⁴.

4. Decrease your intake of added sugar. This means reducing the amount of processed food, including white bread, sausage, cola, and candy, you eat. Foods with added sugar likely boost pathogenic bacteria and increase risk of depression^26,27.

5. Add food high in antioxidants. These include coffee, cocoa, and turmeric. Antioxidants increase levels of Bifido and Lacto, well-known psychobiotics^28,29.

6. Exercise!^30,31

7. Meditation, yoga, and breath practises! These will all help improve your vagal tone, reducing the stress response.

My Book is in Stores!

My book is now on the shelves of stores! What?! It’s absolutely mental and I want to thank everyone who has already ordered a copy! If you haven’t got your book yet, go buy her now!

If you don’t find it in stores, you can request it! And to anyone who can’t afford to buy it, you can request it at your local library :D

Until Next Week,

Nicole x

P.S. Leave a comment with topics you want covered in future weeks!

Rewire With Nicole Vignola

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