We all know the effect our emotions can have on our gut.
The way an interview or stressful meeting, a family row or even change in surroundings can influence what goes on in our bowels. But our digestive system plays a greater role in maintaining our general wellbeing than we give it credit for.

On average, the gut is home to more than 1,000 types of some 100 trillion microbes or bacteria. This colony of bacteria is known as the microbiome. It isn’t harmful. Quite the opposite, actually: its existence is vital to our overall health.

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The inside story
The precise combination and amount of bacteria that make up the microbiome 
is unique to each of us, but scientists have discovered a core set of functions the microbiome performs among healthy people. It extracts and creates nutrients from the food we eat, programmes the immune system and strengthens and maintains the gut wall, blocking outside invaders such as viruses that can cause disease.

The microbiome also helps to produce hundreds of neurochemicals, which the brain uses to regulate digestion, immunity and metabolism, as well as mental processes such as learning, memory and mood. In fact, doctors refer to the gut as the second brain. It’s the only organ with its own nervous system: an intricate network of 100 million nerve cells (larger even than that in the spinal cord). This network is connected with the ‘first’ (or, to you and me, actual) brain via the vagus nerve, which starts in the back of the skull and ends in the abdomen, connecting with the ears, voice box, heart, lungs and stomach along the way.

Nerve cells send and receive messages from one ‘brain’ to the other via neurochemicals produced by the gut microbiome. So when you feel butterflies in your tummy before an important meeting or exam, or get stomach cramps because you’re anxious about a long journey or (dare we suggest) a visit from the mother-in-law, that’ll be them communicating.

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Cause and effect
Both the brain and gut are affected by our emotions and lifestyle choices. Studies show that even mild stress can tip the balance of our microbiome, making us more vulnerable to infection and disease. For example, in a Canadian study, researchers tested the microbiomes of red squirrels living in the wild and analysed the animals’ stress hormones. They found that squirrels living in a low-stress environment had healthier and more diverse microbiomes. ‘Bacterial diversity within animals and people is emerging as an essential component of health,’ explains Professor Amy Newman, senior author of the study.

Now studies are looking beyond what our mind does to our bowel health, and instead are looking at the impact the gut microbiome can have on our mood and mental health. Early lab findings, though mostly related to rodents, show that when the microbiome is manipulated, so is behaviour. Dr Stephen Collins, a gastroenterology researcher at McMaster University in Ontario, found strains of two bacteria – lactobacillus and bifidobacterium – reduced anxious behaviour in mice. In his study, he collected gut bacteria from mice prone to anxious behaviour and transplanted them into mice inclined to be calm.

As a result, the tranquil mice appeared to become anxious.
The research has stretched to humans, too. A recent study published in the 
journal Gastroenterology found healthy women who ate probiotic yogurt twice a day for four weeks reacted more calmly when shown a series of images than those who didn’t eat the yogurt. Professor Mayer, who led the study, believes the results were caused by the bacteria in the yogurt changing the microbiomes of the participants, which in turn modified their brain chemistry.

While still in its infancy, this research opens up the possibility of treatments using beneficial bacteria to treat mood and anxiety disorders via drugs that enhance or mimic their functions. Professor John Cryan, a neuroscientist at University College Cork, goes as far as to predict that bacteria ‘could eventually be used the way we now use Prozac or Valium’.

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Building a healthy microbiome
Of course, what we eat and drink can have an impact on our brain and gut, causing them to release either feel-good or stress signals, 
or a mixture of both. Take alcohol, for example: having one drink may help us to feel relaxed, but downing one too many has the opposite effect.

In his latest book, The Diet Myth: the Real Science Behind What We Eat, Professor Tim Spector draws on his research into bacteria, genetics and diet, and asserts that our growing awareness of microbes is transforming our entire understanding of the relationship between our bodies and the food we eat. ‘The idea that the gut and brain are so closely linked is especially important and gives weight to the need to eat more healthily, to resist processed foods, and to search out a balance in our diet,’ he says.

Tim also suggests that further developing our understanding of the ‘intricate community’ of microbes inside us will help us realise that we have to look after that community much better than most of us currently do. ‘If you treat your gut as you would a garden it will do pretty well,’ he says. ‘If you were starting a garden from scratch, what would you do? It’s about getting back to basics and feeding it good things. It’s the same with 
your body: chemical-laden products and fads can easily deprive your body of some of the nutrients you need.

It’s about diversity, too – the more diverse the microbes, the better your general wellbeing. It helps everything fall into place.’There’s a long way to 
go for research into microbes and mood, but it’s clear these bacteria have a key function in keeping our brain as well as our body healthy.

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