Laura Tilt – The Gut-Brain Connection

What do the bacteria in your belly have to do with your brain? As it turns out, way more than you might expect…

The Gut Brain Axis
If you’re interested in gut health, chances are you’ve heard the words ‘gut-brain axis’. Scientists use this phrase to describe the two-way communication that takes place between the brain in your head and the one in your gut. Yep, there’s a second brain in your belly, and it’s in constant talks with the one up top.

This communication highway controls everything from digestion and immune function to stress response. Even before a meal enters your tummy, the sight, smell and taste of food activates appetite hotspots in your brain, which drive messages to your gut, triggering the release of hormones and enzymes that help you digest your meal.

These chemical messengers (neurotransmitters) travel from the brain to the gut via the vagus nerve – the longest nerve in your body – which spiders from your brain to the depths of your intestines, a bit like a string telephone. Your gut has its very own nervous system, which picks up messages from the brain, and acts accordingly.

Emotions are felt in your gut too. When you experience stress (whether it’s a delayed train or a genuinely dangerous situation), hormones that activate the ‘fight or flight’ response fuel changes in your gut motility. This explains why a job interview can leave you running for the loo.

The Microbiome Link
But this isn’t the only system at play. In recent years scientists have discovered that the trillions of bacteria living in your gut (known as the gut microbiome) have the ability to change your brain’s behaviour.

For example, your gut bacteria are responsible for manufacturing a range of neurotransmitters, including the ‘feel-good’ hormones serotonin and dopamine, which regulate mood and behaviour. In fact, 90 per cent of the body’s serotonin in the body is made in the gut1.

Your gut bacteria also turn the fibre in your diet into compounds known as short chain fatty acids, which appear to protect the brain from stress2,3. They even produce substances that help shape your sleep.

So what effect does all this have on your mental health? As it turns out, much more we previously thought. An increasing number of studies have linked changes in the gut microbiota with changes in the brain. In one study, mice bred without gut bacteria showed changes in anxiety-like behaviour4, leading scientists to conclude that our gut bacteria can impact our ability to manage stress.

Although much of the research has been in animals, there are also clues in humans. For example, research has found distinct differences in the gut bacteria of patients with and without depression.

Getting the balance right
Given the close relationship between the microbiome and the brain, scientists are now interested in whether altering the balance of bacteria in the gut could potentially help manage conditions like anxiety and depression.

This has led to an influx of research into psychobiotics (probiotics that have the potential to alter brain behavior) and poo transplants, where faecal samples from healthy volunteers are transplanted to people with depression.

As exciting as these developments are (!), the truth is we’re a long way off finding out whether these types of treatments are effective – but it’s a promising start.

Poo transplants aside, the good news is there’s plenty you can do to foster a healthy relationship between your biome and your brain – and it’s mostly driven by your diet. Here’s how…

Prioritise Fruit And Veg Scientists from the University of Warwick5 found adults eating seven serves of fruit and veggies a day had the highest reported levels of happiness and wellbeing. There’s lots of possible reasons – one of them being the benefits for your gut bacteria… fruit and veg are rich in fibre, which encourage the growth of beneficial bacteria. They’re also rich in antioxidants that help protect the brain from stress.
Eat a Diverse Diet Determining the balance of bacteria that make up a ‘healthy’ microbiome is still up for debate, but something scientists agree on is that diversity seems important. The same goes for your diet – in one study, people regularly eating 30 types of plant food a week had a more diverse microbiome than those eating 10 or fewer.
Feed Your Bugs It’s still not clear which strains of probiotic bacteria have the biggest effect on mental wellbeing, but strains from the lactobacillus and Bifidobacterium families have shown promise6. Find them in live yogurt, kefir, wholegrains, sourdough, fermented foods, or your daily dose of Symprove.
Make Space To De-Stress Taking time to decompress isn’t just vital for your sense of wellbeing – stress can cause unfavorable changes to your gut microbiome. Make space in your day for activities that help you unwind. Aim to create a regular slot in your day for 10-20 minutes of yoga, mindfulness or a walk in green space to help you maintain balance.

References
1. Jenkins TA, Nguyen JCD, Polglaze KE, Bertrand PP. Influence of tryptophan and serotonin on mood and cognition with a possible role of the gut-brain axis. Nutrients 2016;8(1). doi:10.3390/nu8010056.
2. van de Wouw M, Boehme M, Lyte JM, et al. Short-chain fatty acids: microbial metabolites that alleviate stress-induced brain-gut axis alterations. J. Physiol. 2018. doi:10.1113/JP276431.
3. Bourassa MW, Alim I, Bultman SJ, Ratan RR. Butyrate, neuroepigenetics and the gut microbiome: Can a high fiber diet improve brain health? Neurosci. Lett. 2016;625:56-63. doi:10.1016/j.neulet.2016.02.009.
4. Neufeld KM, Kang N, Bienenstock J, Foster JA. Reduced anxiety-like behavior and central neurochemical change in germ-free mice. Neurogastroenterol. Motil. 2011;23(3). doi:10.1111/j.1365-2982.2010.01620.x.
5. Blanchflower DG, Oswald AJ, Stewart-Brown S. Is Psychological Well-Being Linked to the Consumption of Fruit and Vegetables? Soc. Indic. Res. 2013;114(3):785-801. doi:10.1007/s11205-012-0173-y.
6. Wallace CJK, Milev R. The effects of probiotics on depressive symptoms in humans: A systematic review. Ann. Gen. Psychiatry 2017;16(1). doi:10.1186/s12991-017-0138-2.