Gut feelings are part of a complex system of interactions between the gut and the brain. Imbalances in this system create both physical conditions like IBS, and psychological ones like stress, anxiety and depression.

Stomachs are strange places, home to the butterfly feelings, the tightness or nausea of anxiety, inexplicable pains and bloating, the sinking feeling of having done something wrong or the emptiness of being sad. Often we’re not so keen on them. But our guts are also amazing places, which actually contain their own huge nervous system that’s in two-way communication with the brain, such that mental and emotional states have an effect on gut health, and vice versa. There is also evidence that the bacterial environment of the guts is in two-way communication with our brains and emotional states. Gut feelings are part of a complex system of interactions between the gut and the brain, and imbalances in this whole system create both physical conditions like irritable bowel syndrome and psychological conditions like chronic stress, anxiety and depression.

I very often find myself wanting to work with my clients’ stomachs, and that there is much for them to gain back there. I’ve already written about the psoas muscle in this area of the body, but it’s worth getting to know your belly even more. This article is the first of two looking at this topic. Here we’ll focus on how to think about digestive conditions like irritable bowel syndrome, and we’ll start to look at the ‘second brain’ in the belly. You can find the second article here.

Irritable Bowels are a Mind-Body Phenomenon

Many people experience upset stomachs at various times. When this happens over a longer time, it can get classified as dyspepsia (indigestion), or irritable bowel syndrome (IBS). Dyspepsia often comes with feelings of burning and nausea, while IBS refers to the chronic experience of bloating, discomfort or pain in the stomach and intestines. Around 10-20% of people are reported to be affected by (IBS) and around one in four people have dyspepsia at some point.

The term IBS is somehow comforting, allowing you to put your unpleasant experiences into a box. But it is a largely empty label. It labels the symptoms of disturbance to digestive function, without giving an explanation: there is no discernable medical cause, no physical disorder, no disease. IBS means the system is distressed, but we don’t know why. Because of this lack, patients have often been given the impression that their symptoms are all in their head. But the label’s emptiness doesn’t mean those experiences are not real. It means we need to look at IBS experiences differently.

IBS and Stress, Anxiety and Depression

Correlations between irritable bowel syndrome and a range of psychological conditions have now been well researched. In one study, two thirds of patients said that stress alters their bowel patterns, and half reported abdominal pain from stress. Chronic stress (more than 3 months) experienced before the age of 18 has been shown to be linked with higher rates of IBS, asthma, obesity and high blood pressure. Stress even has an effect on diseases with a physical cause, including Crohn’s disease or ulcerative collitis. And two thirds of people with basically healthy digestive systems say stress gives them stomach aches.

As well as being linked to stress, IBS often correlates with anxiety or panic. About two thirds of IBS patients meet the criteria for one or more psychiatric disorders, especially anxiety and depression. Some link this to the effects of gut disorders on mood, and the anxious anticipation of the next distressing episode. But the link is two-way. Nearly half of people with panic disorders and a third of people with depression have IBS. There is also a correlation between IBS and post-traumatic stress disorder.

Because of these developments, some people claim that anxiety is the chief cause of IBS. But talking about one thing causing the other misses the point. People often think about anxiety in terms of certain patterns of thoughts and feelings, but these do not take place in a vacuum. The feelings and thoughts of anxiety are also physiological processes—changes in levels of hormones like cortisol and neurotransmitters like serotonin—which together constitute what we experience as emotion. As physiological processes, thoughts and emotions also interact with many other processes in your body.

This realisation demands that we look at the whole system. The experience we call anxiety and the experience we call IBS then both appear as ways that we consciously experience how the system is operating. The system is very complex, with many interacting subsystems, but one of these has started to get more attention recently: the brain-gut axis. IBS has started to be seen as a disruption in the brain-gut connection, or a disorder of brain-gut and mind-body interactions. Genetic predispositions are also thought to play a part in IBS, and bacteria in the gut may be involved too (see below), but the brain-gut axis has a big role.

Digestive System

The physical side of the digestive system: the gastro-intestinal tract

The Second Brain in the Belly

The digestive system is made up of such a huge number of nerve cells that it has started to be referred to as a second brain in the belly. There are around 100 million neurons embedded in the walls of the gut, known as the enteric nervous system (ENS). That’s more than in the spinal cord or the peripheral nervous system!

One crucial function of this system is obviously to control digestion onsite, thus freeing up the brain for other tasks. Digestion is a big deal: through it you not only absorb nutrients to gain energy, but also have to block out potentially toxic elements from getting past this inside-outside barrier. All of this requires a lot of sensors to gather information. The ENS stimulates the production of stomach acids and regulates the smooth muscle of the intestines, and can operate partly independently of the brain in your skull.

But as well as digestion, the gut’s nervous system has a big influence on our mood and emotions, directly influencing feelings of sadness, anxiety and stress, as well as physical pain. How (and why) is this possible?

The Belly Talking to the Brain

The gut’s nervous system communicates intensely with your brain, primarily via the vagus nerve. In fact, a stunning 90% of the fibres in the vagus nerve carry information from the gut to the brain, rather than in the other direction. This two-way communication system is referred to as the brain-gut axis.

One of the gut and brain’s major talking points is pain, through creating pain sensations. Nerve communication from belly to brain enables us to “feel” the inner world of our digestive systems, telling us which foods to avoid by communicating pain, nausea, gas and discomfort. Visceral pain is communicated through extensive and complex pathways running from the gastrointestinal tract to the spinal cord, and innervating various parts of the brain that are together known as the pain matrix.

Comfort food! By Andrew Malone (Comfort food) [CC BY 2.0 (], via Wikimedia Commons


As well as pain, the brain and gut together create feelings associated with food. Some are to do with appetite, and are communicated via hormones travelling in the blood. For example, the hormone ghrelin is produced in the stomach and tells us we’re hungry, and the hormone PYY is produced in the ilium (small intestine) and tells us we’re full. Foods also affect our emotional states. In a recent 2011 study, participants “consumed” either a fatty acid or saline solution through tubes that ran through their nose to their belly. Those who had received fats reported half as many sad feelings (and hunger), and their brains showed activity in brain regions known to regulate emotions. In short, the presence of fats in the digestive system acts to lift mood, through influencing activity in the brain. Comfort food has been proven!

The gut also influences our mood and emotional state in other ways. It has been found that stimulating the vagus nerve at different frequencies can either produce anxiety or a strong sense of well-being. Vagus nerve activity has been shown to increase the level of brain-derived neurotrophic factor (BDNF), which is like a kind of super-food for the brain, stimulating tissue regeneration.

Nearly every chemical that controls the brain is also found in the gut, which is why various medications that attempt to affect depression or sleeping disorders throw the digestive system off balance. Altering the mix of our neurotransmitters is a tricky, complicated business for the brain and gut. The hormone serotonin, for example, has become known as one of the ‘feel good’ hormones, without which we go in the direction of depression. In fact, 95% of the body’s serotonin is in the gut. Some have suggested that antidepressants may work on the gut rather than the brain, in particular SSRIs (selective serotonin reuptake inhibitors), which basically increase serotonin levels. They may change gut action, which is then conveyed to the brain via the vagus nerve.


By this point, we’ve seen how interlinked the digestive system is with stress and anxiety, especially showing itself in conditions like IBS, and we’ve started to look at how this interlinking actually takes place. In the second article in this series, which you can read here, we’ll take another step in understanding the link between anxiety and the belly, and we’ll also look at the role of bacteria and the immune system there in our physical and psychological well-being.