Sometimes, we have a “gut feeling” that maybe we shouldn’t be doing what we’re about to do. Sometimes, when we’ve been very scared we admit to our friends that we’ve been “shi***ng ourselves”. When we’re in love, we experience “butterflies in the stomach”. Some of our decisions are not thought through, but “gut reactions”, which doesn’t mean that they are bad decisions. They may be just the right thing to do. Our language has many such figures of speech, referring to the relationship between our emotions and the digestive system. But that’s all they are: figures of speech. Or are they? In the last few years, science has rediscovered the gut-brain relationship as an area of research. The brain is one of our most secure organs, encased in bone, shielded by a membrane – the blood-brain-barrier – to protect it from undesirable substances that may be circulating in the blood. Via the nervous system, it collects information transmitted by our senses and reacts accordingly.
The most overlooked informer of the brain is most certainly the gut. Technically, the lumen, or cavity, of the digestive system, from the mouth to the anus, is still the outside world. Anything that’s in there does not really enter the body until it is absorbed. The digestive system therefore has a huge responsibility in protecting us, and in fact 80% of the immune system is situated in the gut. Anything that comes through is scrutinized before it is allowed in, and in a healthy gut this screening system works really well. Gut and brain are connected via the vagus nerve. In comparison to the brain, the gut receives a lot more information form the outside world, and consequently a lot more information travels up than comes down. If gut health is in any way compromised, however, it is not uncommon for patients to experience mental health issues as well.
During foetal development, the brain, central nervous system (CNS) and enteric nervous system (ENS) are created from the same type of tissue. The vagus nerve runs from the abdomen to the brain stem and is the primary route for information from the gut, mainly provided by gut bacteria. The brain consists of neurons, but there are also neurons in the gut. Neurons produce serotonin, a neurotransmitter, which plays a role in emotions like happiness, contentedness, depression, and aggression. It is a precursor for melatonin, a neurotransmitter required for a good night’s sleep. 95% of our body’s serotonin is in fact produced in the gut. Little wonder then, that chemical imbalances and/or treatment of one have an effect on the other: Side effects of common antidepressants include nausea, diarrhoea and constipation. Likewise, antidepressants don’t just lighten a patient’s mood, but can also improve digestive problems, and addressing imbalances in the digestive system can impact on their mental disposition.
Stress strongly affects digestion, too, not only, but most notably in patients suffering from irritable bowel syndrome (IBS). Even if you do not suffer from IBS, you may have experienced digestive irregularities – more indigestion, more bloating, lose bowels, constipation etc. – when under stress.
The gut microbiome (gut flora) is a fascinating area of research, and although science now knows a lot about it, it has only just scratched the surface. We have a lot of information already about what the microbiome does generally. A lot more is yet to be learned how everyone’s personal gut microbes affect their individual health and wellbeing.
The microbiome consists not just of bacteria, but also yeasts, moulds, and parasites. Those microbes can be good, bad or (apparently) not do anything. If they are ‘not doing anything’ that might just mean that we don’t yet know what they are doing, and interesting things might be found out about them in the future. Most research is done on mice, because it would be impossible as well as unethical to raise humans devoid of gut microbes for comparison. So, can the results be applied to humans? It’s early days, but there is no doubt that there is a connection between gut bacteria and the brain and that some kind of communication is happening.
We know that bacteria help train the immune system in distinguishing between “self” (own body cells) and “foreign”. During early development, gut bacteria influence gene expression, affecting learning, memory and behaviour. All through life, bacteria can influence the expression of genes involved in disease, which means they can affect whether those genes are switched on or off. The microflora is also known to play a role in diabetes, autism and obesity. If you are struggling to lose weight, consider restoring your gut flora. This week’s “Trust me I’m a Doctor” (BBC) showed an example about how one’s individual gut flora can affect the way we metabolise foods.
Gut bacteria do a plethora of other jobs as well: They are able to digest foods that are indigestible for us, and in doing so they provide extra carbohydrates, fats and proteins. Bacteria also produce vitamin B and K for us. Just by their presence, they crowd out harmful bacteria and yeasts, and they ensure proper digestive function. Without our microbiome, we would be in big trouble.
So how big is the population of bacteria inside us? Wherever you turn – even the most respectable sources -, you will find the number 10:1 quoted, meaning that we have ten times more bacteria inside us than own body cells. A very recent article on Science Alert disputes that and states that the real ratio is approx. 1.3:1. Still a lot, but much less than previously thought. You’ve read it here first. ;)
Nevertheless – regardless of their numbers – gut bacteria play a considerable role in our health as well as ill health. If you are suffering from depression and anxiety or other mental health issues, consider a gut healing programme with the help of a trained health practitioner alongside your psychiatric treatment, especially – but not only! – if you also experience digestive disturbances.
To learn more about the gut-brain-axis, click here.