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. This is the second of two articles focusing on this system. The first article, which you can read here, looked at how to think about digestive conditions like irritable bowel syndrome, and started to explain the ‘second brain’ in the belly.

Stress, Anxiety and the HPA Axis

In the first article, we looked at just how much of the communication between the brain and the digestive system is actually going upwards (via the vagus nerve) towards the brain. We looked at how this upwards communication has a lot to do with pain and food, and that the guts also influence our emotional states.

The communication between the gut and brain do not only create but is also influenced by emotional states, especially fear and stress. The “stress response” is the body’s way of trying to reinstate balance after the system has been challenged, getting us ready for action. Physiologically, it is known as the HPA axis, because it links the hypothalamus in the brain to the pituitary gland and then the adrenal glands. The hypothalamus produces a hormone called CRF, causing the adrenal glands to release the hormone cortisol (among others). This creates increased heart rate and blood pressure, decreased appetite, increased muscle tension, and increased available glucose to help with fight or flight actions.

The idea is that when the stress is over, those hormones sink back to normal levels. But if we remain in a chronically stressed state, they don’t sink back. On a physical level, extended exposure to CRF can create IBS, through the stomach and intestine cells becoming extra-sensitive to pain. Chronically high levels of cortisol act to suppress the immune system, reducing your ability to deal with inflammation or getting ill, including gastrointestinal issues.

On a more psychological level, there are strong links between high cortisol and many emotional dysfunctions such as depression and anxiety, post-traumatic stress disorder, as well as eating disorders, alcoholism and obesity. CRF in limbic brain regions is associated with depression and anxiety disorders, especially with increased fear, alertness, decreased appetite and sex drive. High cortisol is linked right frontal brain activity, generating fearfulness, irritability, sadness and withdrawal.

Stress, Anxiety and the Autonomic Nervous System

As well as the HPA axis, fear and stress also stimulate the sympathetic nervous system. This is part of the autonomic nervous system, which regulates organ function. The sympathetic nervous system (SNS) is activated during demanding situations, and creates the fight or flight response, through releasing adrenaline and increasing heart rate and muscle tension (among other things). The parasympathetic nervous system (PSNS) is active when you’re resting, and acts to re-set you after a stress to the system. It tells you that you can return to normal functioning, and reducing cortisol/CRF levels.

The PSNS increases digestive and immune system activity, while the SNS decreases them. The gut’s nervous system (ENS), is actually the section of the PSNS that leads to the digestive tract. The gastrointestinal tract communicates with the central nervous system through the vagus nerve (PNS), the SNS, and the pelvic nerve (PSNS). Stimulating the vagus nerve by diaphragmatic breathing (and relaxing muscles that are constraining this breathing) basically acts to stimulate the PSNS, thus increasing digestion, allowing rest and increasing immune system activity. Activating the vagus nerve is part of what I do in my bodywork sessions.

Nerves of the PSNS, which  puts you into the rest/digest mode, connecting to the spinal column in the center. Cranial nerve X is the vagus nerve.

Bacteria and the Immune System

Your guts are also an incredibly important part of your immune system. In fact, 70-80% of the body’s immune system is within your digestive system; it’s place that gets exposed to a lot of bacteria, via whatever you put in your mouth. Your guts contain specialised immune cells and trillions of “friendly” bacteria (known as gut flora, microbiota or probiotics), which have co-evolved to work symbiotically with us, producing enzymes that break down food. It seems that this bacterial system is also a cornerstone to both mental and physical health.

We don’t arrive in the world with bacteria, but accumulate them throughout our lives until with have a healthy biome. This begins with our contact with the bacteria in vaginal fluids as we are born (cesarean sections are associated with an increased risk of asthma and eczema), and continues through kisses on the cheek, through all the foods we eat. Our guts should contain at least 85% “friendly” bacteria, and can tolerate up to 15% of the unfriendly kind. Unfortunately, this balance is often inverted. We eat highly processed foods, which have much less bacteria in them, and we try hard to make our environments as germ-free as possible.

Without the right level or kinds of bacteria, low-grade, long-lasting inflammatory responses can result, which can lead to a kind of “leakiness” of the intestinal lining, and proteins and carbohydrates that would not normally be absorbed from the intestines end up in the blood stream. This appears to increase the risk of asthma and eczema, as well as obesity and diabetes. It may be that an alteration in the number and kind of bacteria in the intestines contributes to IBS in some people.

Research is also starting to show how gut bacteria communicates with the gut’s nervous system, thus further enmeshing physiology and psychiatry. Poor intestinal flora can contribute to a wide range of psychological conditions, including depression, anxiety, OCD and ADHD. In infancy, the gut bacteria plays a strong role in how the brain is wired, especially in terms of the anxiety and fear responses, i.e. how easily someone is triggered to become anxious.

Some kinds of lactobacillus (a bacterium found in yogurt, cheese, fermented foods and vaginas) have been shown to reduce anxious behaviors in mice. Probiotic treatments (i.e. consuming the friendly bacteria) have also been found to have an effect on OCD and ADHD, and introduction of more bacteria has also been found to change the HPA stress response, although possibly only at an early age.

Research even shows that the gut flora then influences how our genes are expressed. Our genetics give us predispositions, but how these predispositions function on a day-to-day basis is influenced by the gut biome.

And finally…

What I hope you can see through these two articles is a pretty hefty chunk of research showing just how intertwined your physical and psychological landscapes are, in this case centered on the belly. This article isn’t going to give any practical tips on what to do about all of this. My aim is to give you some tools to see things differently, and to motivate you to seek out some of those practical steps. As for what exactly to do, just trust your guts 😉