Have you ever felt butterflies in your stomach when you're nervous? Or get a sinking stomach while having stressful thoughts?
Some thoughts influence the digestive processes in the gut e.g. thinking about eating a delicious meal can make your tummy grumble. But the gastrointestinal tract is also sensitive to emotions, and feelings can even trigger symptoms in the gut. In fact, the communication runs both ways – the gut also communicates with the brain and can influence our emotions.
Only recently microbiologists, neuroscientists and dietitians have revised their understanding of how seemingly separate bodily areas interact. Their bidirectional communication is a rapidly evolving field.
How does the gut affect the brain?
1. The gut microbiota is central to the communication between the gut and the brain. We live in symbiotic relationship with these microbes: we provide them with nutrients from food we consume, and in return they help us in many ways, including supporting our brain development and brain function.
2. Gut bacteria have been implicated in a variety of psychological processes and neuropsychiatric disorders. Disturbed balance in microbial composition, or “dysbiosis”, has been linked with health problems. Recent research suggested that gut bacteria can affect our mood, sociability and stress response.
Potential mechanisms by which the gut bacteria influence the brain include vagal nerve stimulation, interaction with the immune system, bacterially-produced metabolites and neurotransmitters.
Gut bacteria produce molecules that affect how our brain works. For example, certain Lactobacillus and Bifidobacterium produce gamma-aminobutyric acid (GABA), which controls feelings of fear and anxiety and keeps a “busy mind” under control. Some gut bacteria also aid their host in the production of serotonin (which affects the brain to generate feelings of happiness and controls your internal body clock). 
The gut and its microbial profile influence how much inflammation occurs throughout the body and the brain. Inflammation has been linked to low mood, spotty memory and poor concentration, as well as neurological and psychological conditions like Alzheimer's disease, depression and schizophrenia. 
The vagus nerve is another key player in gut-brain communication. It connects the 500 million neurons in the gut to the brain. Nerve signals run in both directions – from the gut to the brain, and the brain to the gut. 
How gut health affects mental health
Recent studies have uncovered the once unknown link between the gut and mental health. As this is a new discovery, scientists are working hard to discover just exactly how the gut influences our mental health.
The trillions of beneficial and harmful bacteria that form part of the gut microbiome usually balance out to an equilibrium that favours the "good" or beneficial bacteria. Trouble occurs when there is an imbalance, and the "bad" bacteria outnumber or outperform the good guys.
These harmful “bad” bacteria create states of inflammation, immune system malfunctions, and disturbed signals to the brain. In adult life, the composition of gut bacteria can be dramatically altered by antibiotics, medications, diet, lifestyle changes and chronic stress. Recent research has shown that significant disruption to the balance of beneficial bacteria in the gut may contribute to psychological conditions including depression, anxiety, ADHD, bipolar disorders, and psychotic disorders like schizophrenia. 
Protecting and nurturing your gut microbiome may improve your mental and emotional health – and vice-versa. A healthy balanced diet high in fibre and the consumption of prebiotics and probiotics can positively affect the balance of your gut microbiome.
How does the brain affect the gut?
We’ve already touched on the impact our gut can have on our brain, but what about the other way around? As they are intrinsically linked, the effects flow both ways, with feelings of stress or nervousness impacting our gut health.
With so many connections, it makes sense that you might feel sick to your stomach when preparing to give a presentation, or experience heartburn during stressful experiences. But just because these symptoms occur when you're stressed doesn't mean that they are only in your head – these gut symptoms are a result of actual physical changes initiated by emotional and mental processes.
Stress and mood changes directly alter the movement and contractions in the gut via the vagus nerve, leading to feelings of constriction or cramping when you are stressed or sluggishness when you feel depressed.
New research has shown that stressful experiences can also promote gut inflammation, reduce immune function in the intestines, and even kill off beneficial bacteria. 
“Emotions, stress and trauma all impact the composition of our gut bacteria. These are really friends with benefits. Knowing the broad spectrum of effects that our gut bacteria have on our health, it becomes ever more important to take care of our diet in order to nurture our gut bacteria. Likewise, a healthy gut microbiome may improve our mental and emotional resilience in stressful situations.”Dr Aleks Maruszak, Brain Program Manager at Clasado
When considering how the gut is connected to the brain, it’s easiest to remember that the gut connection is a two-way messaging system formed through a network of nerves, chemical messengers and gut bacteria.
Signals from the brain and our emotions affect our digestive health, and the gut directly influences our moods, brain health and thoughts. So, listen to your gut – it knows more than you think!