THE GUT MICROBIOME AND ANXIETY

Written by Emily Hohler, BA(Oxon), dipION, Registered Nutritional Therapist and Nature Doc practitioner 

What is the gut-brain axis?

The influence of the gut microbiome on emotions and behaviour has become a popular subject. Many of us have heard of the ‘gut-brain axis’. Nonetheless, the idea isn’t a new one. In the nineteenth century, physicians would refer to the stomach as the “great abdominal brain” or the “great nervous system” even while dismissing the colon as “simply a sewer canal”. We know now that the large intestine is home to the vast majority of the gut microbiome, but we still don’t fully understand the gut-brain axis. The exact means of communication are still being researched.

How these organs communicate

What we do know is that these two organs are connected via various pathways including the vagus nerve, hormones and the immune system, and that communication is bidirectional: the brain sends signals to the gut to regulate digestion, stress responses and much else while the gastrointestinal tract, with its network of neurons, sends signals to the brain. This network, the Enteric Nervous System (ENS), controls digestive functions independently of the brain and spinal cord, which is why we can digest food while unconscious, but it also communicates other information, influencing emotions, mood, cognitive function and overall health.

The role played by the gut microbiome 

The gut microbiome, composed of trillions of bacteria, play a crucial role in this communication. A healthy gut microbiome produces metabolites including short chain fatty acids and neurotransmitters such as serotonin and dopamine that influence brain chemistry, lower inflammation and promote the creation of new brain cells (neurogenesis). The converse is true, with dysbiosis increasing inflammation and impacting neurotransmitter signalling, with negative effects on mood, cognition and behaviour. It is for reasons such as these that the gut-brain access is increasingly being implicated in a wide range of mental health issues from anxiety through to autism spectrum disorder, depression and bipolar disorder.

The link between what we eat and how we feel

NEWROAD's advisory scientific expert, Professor Phil Burnet of Oxford University is at the forefront of research exploring the link between gut health and mental wellbeing and his studies have shown that changes in the composition of the gut microbiome are associated with differing anxiety levels. When certain strains are low or the microbiome is less diverse, anxiety symptoms increase. His research emphasises the importance of eating foods that support a healthy microbiome: a wide range of plants, probiotics and prebiotics, a type of indigestible fibre that provides fuel for beneficial bacteria. Legumes, whole grains, artichokes and sweet potatoes, bananas, apples, berries and pears all contain prebiotics as do onions, garlic, asparagus, artichokes, leeks and chicory root.

Scientific studies 

Growing interest in the gut-brain axis has led to an exponential growth in research since 2000, and Professor Burnet is far from alone. There are now thousands of papers investigating the link between mental health and the gut microbiome. A study published in Nature Microbiology in 2019 found that germ-free mice, lacking gut bacteria, exhibited increased anxiety-like behaviours which were ameliorated when given specific strains of bacteria. In studies on individuals with depression, the most consistent findings are a relative increase in pro-inflammatory bacteria. Professor Jacka’s SMILES trial, published in 2017, found that after three months, a third of those in the dietary intervention arm who followed a Mediterranean diet rich in plant foods, legumes, nuts, extra virgin olive oil and fish, met the criteria for remission of major depression.

Ways to nourish our brains

It sounds obvious, but the brain is the most complex organ in our body and it needs to be properly nourished to thrive. The importance of a healthy microbiome has been outlined above, but we also need to be sure we are eating enough Omega-3 fatty acids, consuming adequate protein for our body weight, and meeting all of our vitamin and mineral needs. Nourishing our brains just about eating the right food. Getting enough exercise, sleep, sunlight and spending time with other people, learning new things and making sure we have time to switch off, relax and play are all important, too. It’s hard to get everything right all of the time, but perhaps the simple act of eating more prebiotic-rich foods could be your first step towards a more balanced and less anxious life.