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Irritable Bowel Syndrome
LESSON 2

What Causes IBS?

VIDEO LESSON

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WRITTEN LESSON

Risk Factors for IBS

There are several risk factors associated with developing IBS. These include:

  • Biological sex - females are three times as likely as males to have IBS.
  • Low socioeconomic status.
  • Psychological co-morbidities such as anxiety and depression.
  • A history of childhood trauma or early life adversity. Examples include abuse, household conflict, and a household member with history of mental illness, substance abuse or incarceration.
  • Adulthood stress including relationship disruptions, financial hardships, work or academic stress, health issues, legal problems or major life transitions.
  • Personal history of chronic pain conditions such as chronic low back pain, chronic pelvic pain, endometriosis, migraines or fibromyalgia.
  • Family history of IBS or other chronic pain conditions.

The Biopsychosocial Model

Diagram: the biopsychosocial model of IBS, showing biological, psychological, environmental, and social factors interacting through the brain-gut axisA diagram of the biopsychosocial model of IBS. At the center, a human figure shows the brain and gut linked by a two-way brain-gut axis, labeled Dysregulation: the two-way signals misfire. Four surrounding factors feed into this axis: Biological, including immune function, microbiome, genetics, and inflammation; Psychological, including stress, mood, and coping; Environmental, including early life, culture, and diet; and Social, including support and life events.

IBS does not have a singular cause but instead is the result of a complex interplay between biological, psychological, environmental and social factors. These factors lead to abnormal communication between the brain and the gut, also known as dysregulation of the gut-brain axis. This abnormal bidirectional communication affects motility or in other words how things move through the gut, gut sensations, the immune system, and the gut microbiome. The concept of all these different factors that influence the development of IBS is known as the biopsychosocial model.

The Gut-Brain Axis

The gut-brain axis refers to the constant communication between the brain and the digestive system. The gut and the brain communicate through multiple bidirectional pathways throughout the body.

In IBS, altered brain-gut communication results in heightened sensitivity to gut signals and amplification of pain or discomfort. In patients with IBS this can manifest in several different ways including:

  1. Abnormal motility or how quickly things move through the gut - this can result in diarrhea, constipation or both
  2. Visceral Hypersensitivity, also known as increase in pain perception in the internal organs including the stomach and intestines. In patients with IBS, normal sensations such as movement of food through the gut or the presence of gas in the intestines feel painful or uncomfortable
  3. Increased awareness, attention and monitoring of gastrointestinal sensations and symptoms also known as visceral hypervigilance. In a patient with IBS this can mean anticipating painful or unwanted symptoms as a way to prevent symptoms, however this often has the opposite effect and can worsen symptoms.
  4. Anxiety and fear about experiencing IBS symptoms known as GI symptom-related anxiety. This can lead to behaviors such as avoiding certain situations due to GI symptoms or increased worry at the start of GI symptoms.

The Gut Microbiome and Post-Infectious IBS

Dysregulation of the gut microbiome plays a major role in the development of IBS. The gut microbiome refers to the ecosystem of microbes such as bacteria, viruses, fungi, parasites, and archaea that live in the digestive tract and influence digestive function.

The gut microbiome can influence gut motility, sensation, secretion of hormones and digestive enzymes, the intestinal barrier, immune responses and brain-gut communication. Microbes in the gut can directly affect the mucus layer in the gut, maintain or damage the gut lining, or activate immune cells in the gut. Gut microbes also produce metabolites such as bile acids and short chain fatty acids that further influence aspects of gut function.

Post-infectious IBS is one such example demonstrating the importance of the gut microbiome in the development of IBS. One in ten people who experience an acute gastrointestinal infection such as food poisoning will continue to experience IBS symptoms even after the infection resolves. The risk of developing post-infectious IBS is higher in women, individuals with psychological co-morbidities and patients who use antibiotics for treatment of their infection.

While there is a strong link associated with gut microbial composition and IBS, there is not a single distinct microbial profile associated with IBS. This suggests that while the microbiome is highly influential in the development of IBS, it is not the sole factor.

Diet and IBS

Diet is another factor that can influence the development of IBS. The food we eat influences the composition of the gut microbiome, gas production, sensation inside the digestive tract, and the speed of digestion.

Furthermore, many people with IBS experience symptoms while eating, or shortly thereafter.

Here are some examples of how the food we eat can influence IBS symptoms:

  • High-fat foods can make the gut work harder and change how quickly things move through your gut. This can result in pain, gas, or urgency.
  • Caffeine increases the motility of the gut which can cause urgency or diarrhea.
  • Alcohol can irritate the gut lining which can cause pain and discomfort. Alcohol also increases gut motility which can result in diarrhea and cramping, as well as change the balance of gut bacteria.
  • Spicy foods can activate nerves in the gut that can cause pain as well as increase the motility of the gut leading to cramping and diarrhea.
  • Certain artificial sweeteners especially sugar alcohols (e.g. xylitol, erythritol and sorbitol) are difficult for the gut to break down. Therefore they act as osmotic agents pulling water in the gut and also get fermented by gut bacteria leading to bloating, gas and diarrhea.
  • Natural sugars such as FODMAPs are poorly absorbed in the small intestine and subsequently get fermented by bacteria in the gut. This can lead to gas production. While this is a natural process, in patients with IBS this increase in gas can lead to distention, bloating and pain.

Hypervigilance or fear around eating is common for patients with IBS, leading to the anticipation of symptoms every time they eat. This can reinforce symptoms and lead to restricted or disordered eating patterns.

What to Expect with IBS?

IBS is a chronic condition, which means most people who have IBS will experience symptoms throughout their lives. Most patients will typically experience a waxing and waning course, where symptoms are worse during certain times, and can be minimal or completely absent during other times. A 2011 study found that IBS patients reported symptomatic episodes that occurred 34% of the time over a 14-day period.

Flares happen when something triggers the digestive system. Environmental factors such as stressors, infection, diet, and lifestyle can play a role in triggering symptoms. Even changes in daily routine, such as travel, irregular sleep, or shifts in exercise habits, can throw the gut off balance leading to a flare. Hormonal shifts can also play a role, which is why many women report IBS symptoms fluctuating with their menstrual cycle, pregnancy, perimenopause and menopause.

Identifying individual triggers and developing strategies to reduce flare-ups is key to successful management of IBS.