I have butterflies in my stomach.
That left a bad taste in my mouth.
This news is hard to swallow.
As these common expressions show, the link between emotion and the digestive system is universal.1,2 But while everyone has felt a knot in the stomach, people with IBS react far more strongly to stress and anxiety.
The modern way of thinking about gastrointestinal illness is using a “biopsychosocial model.” As the name suggests, this model proposes that illness is a result of interacting biological, psychological, and social factors.1 Looking at IBS this way makes it easier to understand how stress—a psychosocial factor—can influence the actions of the gut. The model helps to explain gaps between biomedical research and actual patient experience. Finally, this approach gets clinicians thinking about the range of factors that influence the illness—which might lead to better treatment.
The brain-gut connection
The network of neurons in the gut is so complex that it has been called the “second brain.”3 This brain in your gut is hardwired to the brain in your head, forming what is called the “gut-brain axis.”1 Your brain sends signals downward that influence gut function, and your gut sends signals upward that probably influence your mood.
The idea that the gut has a physical reaction to emotional and stressful stimuli is not new.1 Crude experiments in the early 20th century showed that by changing a person’s emotional state, it is possible to affect blood flow to the gut and the movement of food and waste through the gut. Modern technology has enabled researchers to measure nerve signaling from the gut, evaluate the interaction between the immune and nervous system, measure pain perception, and perform functional brain imaging.1 Cutting edge research is underway to understand how gut bacteria communicate with the gut nervous system—and maybe influence our behavior!4 This field of research is called “neurogastroenterology” and it has provided important scientific evidence about gut and brain interaction.1
It is too early to know exactly what this research means for people with IBS. But these discoveries are certainly intriguing, given that IBS has been linked to a wide range of factors, including stress, gut bacteria, food intolerance, immune changes or inflammation, intestinal infection, and genetics.5
Stress: a trigger and a result
Much has been written about the role of stress in IBS. It is well known that stress and anxiety affect many IBS patients: between 40% and 60% of people with IBS have an overlapping psychiatric disorder.5 Research shows that stress can be a trigger of symptoms and can also result from gastrointestinal distress.
A number of experiments have shown that people with IBS have a greater gastrointestinal reaction to stress than people without IBS. For example, strong emotions and stress causes more problems with intestinal motility in people with IBS than without.1,2 People with IBS have a heightened experience of pain in the internal organs—called visceral hypersensitivity—which gets worse under stress. In lab experiments, researchers create stressful situations such as listening to unpleasant music, plunging a hand into cold water, or creating mental stress. In these situations, people with IBS become more sensitive to non-painful rectal stimuli than control subjects do.2 Stress may make the intestinal wall more permeable, letting bacteria or food particles pass into the bloodstream where they do not belong and causing pain and diarrhea.1 Given the role of stress in triggering IBS symptoms, stress management is one of the recommended treatments for IBS.6
Gut-to-brain communication appears to have a role in altered mental function.1 Increased motility and bowel inflammation or injury send signals to the brain that lead to greater feelings of pain, and contributing to anxiety and depression.
Is stress a cause of IBS?
Some evidence suggests that stress may have a role in the development of a functional bowel disorder.2 One theory is that in a susceptible person, chronic stress amps up central stress circuits. Over time, this causes the systems that help us cope with stress to become dysregulated. These systems become less effective at handling things such as infection, illness, and psychosocial stress. What might make a person susceptible to these changes? Genetics, traumatic early life experiences, and chronic stress are some possibilities.2 However, much more research in humans is needed to understand how stress causes changes in gastrointestinal function and nervous system responses.
Drossman DA. Functional Gastrointestinal Disorders: History, Pathophysiology, Clinical Features and Rome IV. Gastroenterology. 2016;150:1262-1279.
Chang L. The role of stress on physiologic responses and clinical symptoms in irritable bowel syndrome. Gastroenterology. 2011;140:761-765.
Hadhazy A. Think Twice: How the Gut's "Second Brain" Influences Mood and Well-Being. Scientific American. February 12, 2010. Accessed 8/25/16 at: http://www.scientificamerican.com/article/gut-second-brain/
Netburn D. Why we feel emotions in our guts, and what microbes have to do with it. Los Angeles Times. July 8, 2016. Accessed 8/25/16 at: http://www.latimes.com/science/la-sci-sn-mind-gut-connection-20160708-snap-story.html
Qin H, Cheng C, Tang X, Bian Z. Impact of psychological stress on irritable bowel syndrome. World J Gastroenterol. 2014;20:14126-14131.
Wilkins T, Pepitone C, Alex B, Schade RR. Diagnosis and management of IBS in adults. Am Fam Physician. 2012;86:419-426.