Finding the root cause of IBS has been a complicated problem. In recent years, the scientific community has undergone a true evolution in its understanding of functional bowel disorders and IBS.
Their working definition includes a group of disorders or clinical entities characterized by the presence of chronic pain, discomfort, and disordered gastrointestinal function. Although this clinical definition points to actual symptoms rather than root cause, it has proved very difficult to isolate a single factor(s) that triggers IBS.
Researchers believe that these conditions are multi-factorial, and that the symptoms experienced by two different patients, although similar, may in fact result from a number of different root causes.
Five Causes of IBS
Irregular muscle contractions in the intestine
The walls of the intestines are lined with layers of muscle that rhythmically contract in order to move food through your digestive tract. The technical term is called “motility”, and this is how digestion works!
Stronger, long-lasting contractions can cause gas, bloating and diarrhea because your body does not absorb all the water and nutrients from your food.
To the contrary, weak intestinal contractions can slow food passage and lead to hard, dry bowel movements.
Nervous System Damage
Your digestive organs are surrounded by nerves, which make you feel hungry and full. Some studies estimate that your digestive system contains as many nerves as your entire spinal column. Abnormalities in these nerves may cause you to experience increased discomfort when your abdomen stretches from gas or stool. Irregular signals between your brain and intestines can cause your body to overreact to normal changes in the digestive process. The result: pain, diarrhea or constipation.
Skip this next section if technical science isn't your cup of tea.
There are two nervous system pathways: one called the enteric nervous system (ENS), which specifically controls normal GI tract functions; and a second, your central nervous system (CNS), which receives signals from your ENS and regulates general bodily functions. Some studies (via MRIs) have shown that some people with IBS have “overactive nervous systems”
Other research shows that environmental factors also influence the neural signals that are sent back and forth between your brain and digestive system. These factors can trigger nerve impulses that cause IBS symptoms.
Inflammation in the intestines
Some people with IBS have an increased number of immune-system cells in their intestines. Like other suspected causes, this immune-system response is associated with pain and diarrhea.
IBS can develop after a severe bout of diarrhea (gastroenteritis) caused by bacteria or a virus. IBS might also be associated with bacterial overgrowth in the intestines. One example of a bacteria species that can cause gastroenteritis is Campylobacter jejuni (you can find an exhaustive list here). Further, studies have found that this bacteria produces a toxin which can disturb bowel function.
Studies estimated that people who had a GI infection were six times more likely to develop IBS within one year and four times more likely over a three-year period. However, there were two mitigating factors: people over the age of 60 had about 1/3 the risk of those aged 19–29 to develop PI-IBS. Vomiting during the initial illness (one of the ways the body tries to rid itself of harmful germs) also reduced the risk of PI-IBS by around 50%.
GI infections can directly cause additional inflammation and elevated nervous system activity. Inflammation is a natural part of your body’s immune system response to infections and viruses. Unfortunately for some people, even after your body has cleared the infection, your GI system may remain inflamed for extended periods of time.
Also, serious infections may damage the nerves along your GI tract. For some, this nerve damage can be the cause of post-infection IBS.
Changes in bacteria in the gut (microflora)
Microflora are the "good" bacteria that reside in the intestines and play a key role in health. There are literally billions of bacteria cells in your body helping you digest your breakfast, lunch, and dinner. Your body’s symbiotic bacteria handle four main functions:
- Protecting against infection by “bad” disease-causing bacteria
- Helping develop your guts specialized the immune system
- Processing your food into micronutrients that your body can’t produce on its own
- Together, the normal intestinal bacteria are often referred to as the gut flora (or microbiota). A number of factors may disturb the mutually beneficial relationship between the flora and the body. When this happens, bacteria that can cause disease may take hold.
Some researchers, including Dr. Emeran Mayer, MD, believe that a rich and healthy diet promotes the “good” microflora bacteria that keep you feeling light and airy.
Research indicates that microflora in people with IBS might differ from microflora in healthy people. As introduced in the previous section, it’s not all bad news. If you have suffered from a GI infection, try taking probiotics. This scientific review found that adding probiotics relieved PI-IBS symptoms and helped people return to normal digestion. Other multi-study reviews also found that probiotics can help restore normal bowel function after an infection. While it is likely that IBS is actually a few different conditions that all “show” the same symptoms, “resetting” your digestive system with prebiotics and antibiotics can restore normal function.
Relieving the Causes of IBS
These five IBS causes are all related. The surprising part is this: what you eat does not cause IBS. Rather, certain foods only trigger your IBS symptoms.
Instead, IBS is caused by a number of conditions that interfere with normal digestive tract function. Nerve damage, infections and changes in your gut bacteria lead to the general inflammation that triggers IBS' symptoms. Outside of inflammation-triggered IBS, abnormal digestive (too fast or too slow) can also cause IBS symptoms.
Luckily, probiotics, antibiotics, and change in diet (low FODMAP) can help alleviate IBS's symptoms and restore normal digestive system function.
To read more about foods to avoid, foods to eat, and how to make easy changes to your IBS diet to mitigate your symptoms, download our IBS Nutrition Guide.