Impact Of Stress On The Gut

Introduction

Does stress ever bring about a knot in your stomach? 

We all experience stress from time to time, and in these instances, our hormones may fluctuate and cause unwanted symptoms in our stomachs. 

Research shows that there is a strong link between our gut and brain through the central nervous system (CNS).¹ In cases of chronic stress or anxiety, our body’s normal balance (homeostasis) is perturbed which may lead to long-term issues. 

The way our bodies respond to stress involves a number of biological processes, and the inability to manage stress may aggravate disorders of the digestive tract. Therefore, it is important to take appropriate measures in reducing stress to help curb these symptoms and aid healthy digestion. This article will explain the impact of stress on our digestive system and tips for preventing stress-induced gastrointestinal disorders.

Effects of stress on the digestive tract

The human gut is rich in microorganisms, harbouring approximately 10¹³-10¹⁴ of them – >100 times the cells that make up our body. The vast majority of bacteria reside in the colon and these are particularly amenable to stress. The microbiota, gut, and brain communicate through the gut-brain axis in a two-way, or bidirectional manner, involving the autonomic nervous system (sympathetic ‘fight-or-flight’, parasympathetic ‘rest-and-digest’, and enteric ‘small intestine’). The parasympathetic (involving the vagus nerve) and the sympathetic pathways convey sensory information to the CNS to regulate motility through the gut-brain axis impinging onto the enteric nervous system, which controls most of the gastrointestinal system. The gastrointestinal tract enables digestion under the control of the enteric nervous system. 

The vagus nerve, also known as the ‘wandering nerve’, is the principal component and the longest nerve of the parasympathetic nervous system. Its main function is to serve as a highway to communicate messages between your gut and brain (i.e. the gut-brain axis) and kicks into action when our body is in ‘rest and digest’ mode. The vagus nerve's role is to sense the metabolic status of our gut microbiota and convey this information to the brain which will generate appropriate responses. The vagus nerve stimulates our digestive organs by:

• Producing stomach acid and facilitating peristalsis
• Increasing bile secretion to allow digestion of fat
• Balancing blood sugar through glucose production¹

However, stress can change the activity of the vagus nerve and have undesirable effects on our digestive system. In times of stress, your liver can also produce more glucose for a boost of energy, but when stress becomes chronic, your body may not be able to adapt to this surge of energy. Therefore, this can increase your risk of developing type 2 diabetes.² 

Other direct consequences of stress on the gut:

• Reduced blood flow to the intestines
• Increased intestinal permeability (leading to a ‘leaky gut’, potentially letting toxins enter)
• Increased activation of the immune system (leading to chronic inflammation)³

The vagus nerve is at the interface of the gut-brain axis, and an anti-inflammatory pathway has been described where activation can dampen inflammation, reduce intestinal permeability, and have a positive effect on the gut. Therefore, it is important that we engage our vagus nerve to ultimately keep stress at bay and our vital organs healthy.

Hormonal changes caused by stress

Hormone imbalances due to stress can impact the function of our gut microbiome, leading to digestive discomfort. During stressful periods, the brain engages your sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis signals to your adrenal glands, facilitating the release of adrenaline and cortisol. These stress hormones greatly impact our digestion, preparing our body for ‘fight-or-flight’ – resulting in either the slowing of digestion (constipation) or speeding it up (diarrhoea).

Physiologically, our bodies will reduce the production of enzymes required for digestion and inhibit the production of stomach acid (hydrochloric acid). In these cases, we are unable to metabolise and break down ingested proteins, which can cause bloating and digestive discomfort. Furthermore, high cortisol levels reduce IgA, an antibody part of the innate immune system. This can lead to bacterial proliferation in the gut and cause food intolerances, IBS, and intestinal permeability.⁴ Another hormone that may be affected is serotonin. Serotonin receptors in our gut may be affected when the HPA axis is dysregulated and in turn influence gut motility and general mood, such as anxiety and depression, which are often correlated with irritable bowel syndrome and other digestive conditions.⁵ 

Oxytocin is an anti-stress hormone that is released from the hypothalamus in the brain. Studies have shown that oxytocin can play a role in the response of the gastrointestinal system to stress. Activation of these oxytocin pathways can reverse the delay of gastric emptying (usually occurring in response to stress) and increase muscle contractions (motility) of the stomach.⁶ In order to identify targets for more effective treatments of disordered gastric responses to stress, it is important to understand how stress usually affects the functioning gut.

Symptoms of stress-induced stomach issues

The effect of stress on your gut depends on the length of time we may be experiencing stress, for example:

• Short-term stress can slow digestion and lead to a loss of appetite
• Long-term stress can trigger GI disorders like constipation, diarrhoea and indigestion
• Chronic stress may lead to IBS or stomach ulcers

Chemical signals are continually being passed between the brain and the gut, and our ‘vagal tone’ (associated with vagus nerve activity) is particularly important in supporting our body to relax and maintain our overall physical health. Disturbances along this pathway (caused by stress and anxiety) can trigger various symptoms as a result. This is very common for many people, and studies have shown that generalised anxiety disorder is five times more common in people with IBS.⁷  Other symptoms of gastrointestinal disorders include bloating, abdominal pain, and stomach cramps.

Coping with stress-induced stomach issues

The key to better digestion is stress management, as it can lower gut inflammation, ease GI stress, and allow our bodies to absorb all the nutrients we need. Activation of our vagus nerve serves to reduce stress and anxiety, as well as increase γ-aminobutyric acid (GABA), a neurotransmitter in the brain that helps us relax. Activating the vagus nerve and kicking our vagal tone into action is achievable by a number of interventions (both physical and psychological).

Ways to improve stress-induced stomach issues

Microbiota modulation: maintaining good levels of pre and probiotics

• More pre-biotics in our diet: food for healthy bacteria in our gut is found in fibrous vegetables, and are important for feeding the bacteria that produce essential metabolites and healthy digestion.
• More probiotics in our diet: restoring the natural balance of bacteria in our gut. The bacterial strain Lactobacillus rhamnosus was shown in animal studies to support optimal levels of the receptors of the calming chemical GABA, which is mediated by the vagus nerve⁸
• Maintaining a healthy diet with natural sources of dietary fibre or magnesium to manage cortisol levels

Yoga or meditation

• An increase in vagal tone from mindfulness-based stress reduction techniques such as yoga and meditation have been shown to reduce anxiety and depression, as well as post-traumatic stress disorder (PTSD)^9,10 
• Diaphragmatic breathing exercises can stimulate the vagus nerve and reduce our body’s response to stress¹¹
• Moderate and sustainable physical activities can restore balanced gut-brain axis communication.

Cognitive behavioural therapy

Cognitive behaviour therapy (CBT) may be an option to reduce anxiety and stress by helping you learn to substitute negative thoughts with positive ones. Studies demonstrate that patients who received CBT reported a higher quality of life, as well as lower levels of depression and anxiety.¹² 

Seeking a doctor's advice: You should contact your GP if your digestive issues may be caused by something else, especially if they haven’t improved within a couple of weeks.

Summary

Our bodies are highly amenable to stress and as a result, our digestive systems can be massively impacted. The reduction in vagal tone has shown importance in the pathology of IBS and related gastrointestinal diseases, therefore it is important to manage stress and restore a homeostatic gut-brain axis.