There are over 140,000 different microorganisms in your gut – and they can all impact your mental and physical health. Here’s all you need to know about the link between your gut and your brain.
How many times have you been told to trust your gut? When it comes to a new job, a dumped lover or a big move, that feeling has a lot to answer for. Although we put it down to instinct rather than a logical rationale, there’s more science behind how our gut impacts our feelings, moods and emotions than we realise.
Often dubbed our second brain, scientists have discovered that the gut also houses our unique gut microbiome (GM). Created within the first 1,000 days of life, our GM quickly develops into a sophisticated neural network, transmitting messages to our brain from trillions of bacteria. Recent research published in the journal Cell suggests that there are 142,809 different types of gut genomes, all of which are integral components in the human gut ecosystem.
The brain uses these strains and organs to help regulate basic physiological and mental processes such as learning, memory and mood – and manufactures around 95% of the body’s supply of serotonin (the happy hormone). Another study even suggests that eating a balanced diet (such as the Mediterranean diet) and avoiding inflammation-producing foods may be protective against mental health conditions such as depression. And a 2022 paper found that those who took probiotics alongside antidepressant medication showed greater improvements in mental health and mood.
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“Gut health is revolutionising our approach to health and looking after your gut is one of the most effective ways to transform your overall wellbeing,” says Dr Megan Rossi of The Gut Health Doctor and author of Eat Yourself Healthy.
“When we talk about gut health, we mean the functioning of your entire nine-metre-long digestive tract. That’s the tube that delivers your food from entry (mouth) to exit (poop). This involves digestion and absorption of food, as well as our gut microbiota which are incredibly powerful – we couldn’t survive without them.
They produce vitamins, hormones and impact our mental health, as well as being linked to our heart health, skin health and 70% of your immune cells. A lot of people say ‘you are what you eat’, but actually, you are what you digest. That’s because even if you have the ‘healthiest’ diet, if you don’t have a good gut lining, you’re not going to extract the nutrients efficiently.”
People say ‘you are what you eat’, but actually, you are what you digest. Even if you have the ‘healthiest’ diet, if you don’t have a good gut lining, you’re not going to extract the nutrients efficiently.
The connection between the gut and the brain
While the thought of trillions of micro-organisms busying themselves in our gut and chatting away to our brain is difficult to imagine, Neurogastroenterology Professor Qasim Aziz of London Digestive Centre (part of The Princess Grace Hospital) explains that it’s a little more complicated.
“Gut microbes communicate with every part of the gut itself such as the lining of the gut (or epithelial cells), the nerves and its immune system. All of these elements are in communication with the brain through the nerves, hormones and immune cells that pass between the two organs. So, if a person is stressed or depressed for any reason, that can affect the function of the gut. For example, in acute stress, it is not uncommon for people to lose appetite or develop diarrhoea. This is because areas of the brain that control anxiety and depression also receive nerves that control gut function and hence, there is reciprocal interaction between the brain and the gut.”
The nerve in question is in fact the vagus nerve – a communication highway that connects our brain and our gut (and almost every other organ in between). It’s responsible for keeping the body in the know at all times – from the fight or flight response to assessing potential risk factors (there’s that gut feeling again). “Long before science connected the two, we were using gut functions to describe our feelings and emotions: ‘I’ve got butterflies in my stomach’; ‘You don’t have the guts for it’; ‘I can’t stomach that’,” Dr Rossi explains. “The latest evidence suggests that tapping into our gut–brain axis could play a pivotal role in our mental health and, with one in four of us predicted to experience a mental health event this year alone, our gut health really is something more of us should be taking into consideration.”
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So, what happens when, like all relationships at some point, communication breaks down? With the gut having its own nervous system of anywhere from 50 to 100 million nerve cells, there’s bound to be the odd biological disagreement. Dr Filip Koidis, a nutritionist from W1 Nutritionist, explains that while there’s not a blanket optimum amount of microbes we should strive for, there’s a unique combination for every individual that we need to keep in a delicate balance.
While diet and antibiotics play a part in diminishing our gut health, destroying good bacteria as well as bad, stress and anxiety can also cause microbes to over-produce. This can then cause “the inner lining of our gut wall to become inflamed or irritated, leaking undigested food and toxins into the body which can make our immune system react and burden our brain and liver,” he says.
Generally speaking, a higher level of GM diversity (the number of different microbes we have) is associated with better overall health. Dr Rossi likens it to a football team – you don’t just want super-star strikers, “the more diverse your GM, the greater the breadth of skills your GM ‘team’ possesses. We don’t just have bacteria too, our GM includes other types of microbes, such as fungi, viruses and parasites which live in our gut too, and we think they work together synergistically to play a role in our health.
It’s similar to a thriving garden – if you have all the same type of plants and a certain disease comes along, it could wipe out your entire garden. In comparison, if you have a diverse range of plants, it is very unlikely that one disease has the right array of ‘weapons’ to wipe them all out – some will naturally be resistant. The same goes for your GM.”
With a strong gut-brain relationship that relies heavily on one another’s good health to function, it conjures up the chicken or the egg dilemma as to what to take care of first. “Both! This communication between our gut and our brain (our emotions) goes both ways,” Dr Rossi explains. “Not only allowing our brain to send messages to our gut via the vagus nerve, but also enabling our gut microbes to send signals back up to our brain (like a mobile phone).
When we’re mentally stressed (because our brain is telling us we are), this can alter the communication via the gut-brain axis and can trigger physical stress along your intestine, resulting in gut symptoms (such as diarrhoea, constipation, abdominal pain or intolerances) for some. Similarly, gut symptoms can be rather distressing, which can trigger the brain via the gut-brain axis.
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In some people with bloating, for example, the tummy pain can trigger the brain to over-contract the diaphragm in an attempt to relieve the gut distress. Dr Rossi also sees, both from clinical trials and anecdotally with her patients that improving gut symptoms can have a profound positive impact on people’s mental health, although the exact mechanisms are still unclear.
Maintaining a harmonious environment for our gut microbes to flourish is no mean feat and experts insist that it’s a multi-faceted task, starting with the below solutions:
How to improve your gut health
“Sleep disturbance, high stress levels and lack of movement have all been shown to impact our gut microbes,” Dr Rossi explains. “This is because your GM also exhibits a sleep-wake cycle, known as the circadian rhythm. Try improving your sleep quality by setting a regular bedtime routine with relaxation exercises, limiting caffeine after 3pm and scheduling ‘worry time’ during your day to write down your thoughts and free up your head space before bed.”
“Interestingly, the brain initiates digestion before the gut – this happens as we start secreting digestive enzymes from the moment our senses (vision and smell) are stimulated,” Dr Koidis says. “Our gut microbiota produces other chemicals (like short chain fatty acids) when digesting fibre which can have a direct effect on our brain function.
Focus on a variety of plant-based foods – studies have shown that we should aim for 30 different types of plant-based foods a week, full of gut-loving fibres like vegetables, fruit, legumes, grains, nuts and seeds.
Also, increase your intake of traditionally fermented foods that contain live cultures such as yoghurt, kombucha, kefir and sauerkraut – which promote the growth of good bacteria. Avoid restrictive diets, especially the ones that have declared a war against gut-health essential carbohydrate sources. Restricting diets can starve your gut-loving bacteria and negatively impact your gut health.”
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“If a person is stressed or depressed, that can affect the function of the gut such as decreased appetite or diarrhoea. This is because areas of the brain that control anxiety and depression also receive nerves that control gut function and hence there is reciprocal interaction,” Professor Aziz warns. Mindfulness exercises such as meditation, yoga and digital detoxes can help calm the mind.
“While antibiotics are incredibly important, they also harm the beneficial bacteria and, in some people, these changes seem to be irreversible,” Dr Rossi explains. “Research suggests many non-antibiotic medications can potentially impact the growth of our gut microbes too. So, if you’re taking medication because it’s easier than changing your lifestyle (for example, reducing alcohol intake or relying on sleeping pills) then it may be worth rethinking this, under the guidance of your doctor.”
“We all know exercise is good for us – and our gut microbes benefit from it too,” Dr Rossi says. “Exercise helps to regulate your pooping habits and increase the diversity of your gut microbes, which is linked to better overall health. Sustained exercise is key, so move your body regularly, getting your heart rate up for at least 30 mins most days. Gut-directed yoga has also been found to be as equally effective as diet changes for reducing IBS symptoms.”
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