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Understanding the causes and symptoms of Irritable Bowel Syndrome

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Answering some basic questions can give a better understanding of the causes and symptoms of IBS. This short Q&A will address the most common questions about what causes IBS, focusing on the main symptoms and how specific lifestyle behaviors can worsen these symptoms. In a similar article, we deal with the most preferred treatments, both medical and in terms of lifestyle changes.


What is irritable bowel syndrome (IBS)?

Irritable Bowel Syndrome (IBS) is a chronic condition that affects the large intestine. In a healthy gut, the muscles that line the walls of the intestine rhythmically contract in order to move food through the digestive tract. In IBS, these contractions may vary. If they are more robust and last longer than normal, they can cause gas, bloating, and diarrhea. If they are weaker, this will slow down the passage of food and lead to hard, dry stools and constipation.

To understand IBS, it’s essential to distinguish it from other kinds of bowel disorders, like Crohn’s Disease or Ulcerative Colitis. Those and other similar conditions are inflammatory or autoimmune diseases, where the body’s immune system mistakenly attacks healthy cells, causing inflammation and, in the case of Crohn’s and Ulcerative Colitis, with the potential of damaging the lining of the entire digestive tract, not just the lower bowel. IBS is primarily a functional disorder, meaning it’s a problem with bowel function rather than an issue with structural or biochemical abnormalities. IBS doesn’t cause changes in bowel tissue or increase the risk of colorectal cancer like those diseases can.

IBS is a complex disorder with various potential causes and contributing factors. Both genetics and psychological elements can play a significant role in the condition. This complexity makes IBS challenging to manage and treat, requiring a comprehensive approach tailored to the individual.

What are the causes and symptoms of IBS?

While the precise cause of IBS isn’t known, and it may vary from person to person, a variety of common factors appear to play a role, including genetics, food intolerances, stress, hormonal changes, and certain medications.

Scientists have developed an understanding of the causes and symptoms of IBS, and now believe the combination of physical and mental health factors creates some potential triggers:

  • Nervous system – during the digestive process, signals are generated from nerves in the digestive system that can cause an over-reaction to the normal changes that occur in the digestive process. These may cause discomfort when your abdomen stretches from gas or stool. Mixed-up signals between the brain and the digestive system can cause the body to overreact, resulting in pain, diarrhea, or constipation.
  • Severe infection – IBS can develop after a severe bout of gastroenteritis caused by bacteria or a virus. The typical symptoms of a gut infection are diarrhea, nausea and general weakness. It might also be associated with a surplus of bacteria in the intestines, also known as bacterial overgrowth.
  • Dysbiosis – in which there have been changes in gut microorganisms. The gut is full of symbiotic bacteria, viruses, and fungi. The environment is a delicate ecosystem, and any imbalance can lead to people with IBS suffering more than those without the disease
  • Genetic factors – IBS is not considered a genetic disease, but studies have found it can run in families, indicating that genetics may play a role in developing IBS. This means that people are more likely to have IBS if a close family member also has the condition. Research into the specific genes involved is ongoing, but multiple genes are likely contributing to the development of IBS.

Regardless of the cause, the most prevalent symptoms of IBS can be one or more of the following:

  • Stomach pain and cramping
  • Onset of diarrhea, constipation or sometimes both
  • Bloating and swelling of the abdomen
  • Flatulence (excessive wind)
  • Experiencing an urgent need to go to the toilet

Is Irritable Bowel Syndrome mostly psychosomatic?

The onset of IBS is strongly linked to a person’s psychological health. Stress and anxiety can trigger symptoms of IBS, and those with IBS are often found to have higher levels of stress, anxiety, and depression than the general population. It’s a chicken-and-egg situation: stress can trigger IBS symptoms, but having IBS can also cause stress and anxiety, creating a vicious cycle.

There’s also been shown to be a strong connection between the gut and the brain, known as the gut-brain axis. This bi-directional communication pathway means that stress and mental health issues can affect gut function, and changes in gut function can, in turn, impact mental health. This is often referred to as a “brain-gut disorder” as disruptions or miscommunications in this pathway could lead to conditions like IBS.

Using terminology like “psychosomatic” illness doesn’t mean that the condition is “all in someone’s head.” Rather, it means that psychological factors can contribute to physical symptoms. In the case of improving the understanding of the causes and symptoms of IBS, this can be seen where emotional stressors or psychological conditions may contribute to the severity and frequency of symptoms.

What is the difference between IBS and FIT?

There is only a slight connection between IBS and FIT. IBS is a bowel condition (irritable bowel syndrome). FIT is an abbreviation of the Fecal Immunochemical Test. This non-invasive, easy-to-use test is meant to detect the presence of blood in the stool. It is typically recommended starting at age fifty for people with no more than average risk for colorectal cancer, or earlier for those with higher risk factors. One of the characteristic differences between IBS and other bowel disorders, such as Crohn’s Disease and Ulcerative Colitis, is that they present a much higher risk of colon cancer. In contrast, there is no such elevation for people with IBS.

How do lifestyle factors affect digestive health?

Much of the relationship between lifestyle and IBS comes from the bi-directional ‘gut-brain axis’ communication system. The gut-brain axis (GBA) is a symbiosis that integrates neural, hormonal, and immunological signaling between the gastrointestinal tract and the central nervous system. The GBA involves complex crosstalk between the enteric and central nervous systems, fundamentally influencing several aspects of human physiology, including digestion, mood, health, and disease states.

This network is quite intricate and involves various mechanisms, including:

  • A neural component involving the vagus nerve, which transmits signals between the gut and the brain, providing real-time information about the state of the digestive system
  • An endocrine component in which the hypothalamic-pituitary-adrenal (HPA) axis also plays a key role. The gut and the brain communicate through endocrine signaling, with the gut producing around 20 different hormones that can affect brain function 
  • An immune component, in which the gut-associated lymphoid tissue (GALT) can release signaling molecules, called cytokines, that can reach the brain and potentially impact mood and behavior.
  • The trillions of bacteria that live in the gut (the gut microbiota), which is the diverse community of microorganisms inhabiting our gut, can influence the signals sent to your brain, affecting stress responses, mood, and behavior.

In the context of irritable bowel syndrome (IBS) and other functional gastrointestinal disorders, disturbances in the gut-brain axis are considered a critical factor. Changes in gut microbiota, intestinal permeability, immune activation, and aberrant central nervous system processing have been identified in various patients.

Is irritable bowel syndrome related to eating junk food?

It’s important to understand that while diet doesn’t directly cause IBS, it can trigger bouts and flare-ups. The relationship between what a person eats and how their gut behaves is key to understanding and managing this condition.

Food passes through the digestive system and is broken down in multiple steps along the way. However, for people with IBS, certain foods might not get processed as smoothly as others, leading to uncomfortable symptoms. 

  • High-fat foods, especially saturated fats, might cause issues. Fat slows digestion, and that can lead to uncomfortable symptoms coming from strong contractions of the gut, leading to cramping, acid reflux and diarrhea
  • Foods like certain beans and lentils, wheat and other such foods that are rich in insoluble fiber can cause the gut to stretch and distend, which may lead to the bloating and discomfort that some people with IBS experience. Fiber can be both an ally and an enemy in IBS. Insoluble fiber, found in whole grains and vegetables, can help add bulk to the stool, aiding those struggling with constipation. However, it can also exacerbate symptoms in people with diarrhea-predominant IBS-D
  • Caffeinated beverages (tea as well as coffee), alcohol, and carbonated soft drinks may contribute to symptoms by either stimulating the intestines or causing gas and bloating
  • Ultra-processed foods (like chips, canned meats, cookies, and crackers) are filled with additives and preservatives and are often fried and/or high in fat. These foods can irritate the gut and trigger IBS symptoms. If it comes in a box or a bag, it’s best to avoid it and find something less processed to munch on
  • Sweeteners in products such as candies, gum, and mints belong to the family of carbohydrates called polyols. They can be resistant to digestion and so often cause bloating and diarrhea in people with IBS.

Everyone with IBS is different, and what causes trouble for one person might not cause trouble for another. Keeping a food diary can be a practical way to track what foods might trigger symptoms.

What does constipation mean for someone with IBS?

There are two primary forms of IBS. In both, there are feelings of bloating caused by gaseous accumulations in the lower bowel. In one, the predominant symptoms are diarrhea and runny stools. This is called IBS-D. On the other hand, IBS can cause constipation as well as diarrhea. Constipation-predominant (IBS-C) is estimated to affect around one-third of all people who suffer from the disorder. 

People with IBS-C share the following symptoms with people suffering from chronic constipation:

  • Have to make a great effort to defecate
  • Make lumpy and hard stools
  • Feel like bowel movement is blocked
  • Feel like the bowel remains full after movement     
  • Feel bloated and full of gas and bloating

For people with IBS-C, the differentiating symptoms from those with chronic constipation alone would usually be stomach ache and discomfort that reduces after a bowel movement, alternating bouts of diarrhea and constipation, and nausea.

Once someone develops IBS, is it permanent?

Typically, IBS is a life-long condition that cannot be cured. However, changes in diet and lifestyle improvements like exercise, relaxation training, behavioral and psychological therapies and other non-pharmacological treatments can reduce the frequency and degree of attacks.

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