Why do I have IBS?

why do I have IBS

IBS sufferers often ask “Why do I have IBS?” or “Why now?” when trying to find out how their IBS started. So let’s piece together that puzzle, looking at the probable and possible causes of IBS

The first point to consider when you think about all these factors is that IBS is what is termed a functional gut condition, so the causes of the condition impact on the functioning (not the structure) of the gut. What this means for IBS sufferers is that the symptoms of the condition are the problem to be managed, but IBS does not increase risk of other gastro-intestinal conditions such as bowel cancer. 

The following information may not provide all the answers you need to completely resolve IBS, but hopefully it will assist in understanding where and how it may have developed.


REASON 1: Blame your parents? Hereditary and genetic factors

Do you remember your mother or father having a “funny tummy”? Relatives of an individual with IBS are two to three times as likely to have IBS, with both genders being affected. Family studies indicate that the inheritance of IBS seems to be genetic rather than being explained by psychological traits (1). Those genetically predisposed to inflammation may be particularly susceptible to IBS (2). Women are more likely to be diagnosed with IBS than men, but there is uncertainty about whether this means more women have IBS. Men do not report or recognise the symptoms as a medical condition, for example men MAY consider excess wind to be normal.


REASON 2: Gut residents

IBS symptoms can be triggered by fermentation of undigested carbohydrate by bacteria in the lower gut. While the resulting gases can be beneficial to health, they can cause problems in those with a super-sensitive gut or if the balance of bacteria is not ideal. Disruption to the delicate balance of gut “residents” can cause all sorts of problems. It is well known that antibiotics disrupt the balance of gut bacteria (3). 

A study published recently showed that people treated with antibiotics for a non-gastrointestinal infection were twice as likely to develop IBS or a similar functional gut condition (3). It is possible that changes to the number or quality of gut bacteria may be involved in triggering ongoing gut issues. That is not a reason to avoid antibiotics at all cost, but more an explanation of possible triggers for IBS symptoms.


REASON 3: Gut “bug” or “gastro” or parasite

The development of IBS after an episode of acute gastroenteritis (also known as a “tummy bug” or “gastro”) can result in what is known as post-infective IBS. Several well designed studies have shown that a bout of “gastro” leads to IBS in 7–30% of patients (2). This leads us to question whether other causes of gastroenteritis such as virus and parasites may also lead to IBS. 

During infection (and inflammation), the lining of the gut becomes more permeable and bacterial populations move and change. It is possible that these changes are maintained to some extent, and be partly responsible for the development and/or maintenance of IBS.


REASON 4: Gut Motility

Changes in the action of the smooth muscles of the gut can also result in IBS symptoms. This is called gut motility, and it can cause changes to gut bacterial populations, which in turn can affect gut motility, and so it goes on. Increased gut motility can cause food and liquid to move through the gut to quickly, resulting in diarrhoea and decreased gut motility can result in constipation. If either of these symptoms last for more than three months, they are classed as IBS symptoms, and some people with IBS suffer with both constipation and diarrhoea (often in quick succession).


REASON 5: Inflammation and immune system

The gut lining is the “meeting point” between the outside world and the bloodstream, it makes sense that the gut needs to be highly tuned and sensitive to things that might be considered harmful or foreign to the body. It also makes sense that disturbances to digestion or the immune system or the nervous system can impact on the gut and vice versa. 

Therefore, conditions that affect the immune system (whether they relate directly to the gut or not) can impact on IBS risk and symptoms, by impacting on gut bacteria or gut motility. Further, medications used to treat inflammation can further disturb gut functioning, compounding IBS symptoms. The role of anti-inflammatories in gut disturbance will be discussed in detail in future blogs.


REASON 6: Stress

The gut has “a mind of its own”. The enteric nervous system sends and receives impulses, records experiences and respond to emotions just like the brain and is influenced by the same neurotransmitters. What happens in the gut impacts on the brain and whatever is going on in the brain affects the gut. The extent to which the gut and brain interact depends on the sensitivity of one to the other . 

Gut brain hypersensitivity is the term used for when the gut and brain become too sensitive to each other, and one minor emotional stress or gut reaction can be interpreted as severe or painful. For this reason, increasing responses to emotional stressors or sensitivities of the gut can impact on IBS symptoms.


REASON 7: Diet

Some dietary factors can make IBS more likely and some can make the symptoms worse. While this does not mean that diet is a cause of IBS, it is worth summarising the dietary factors that impact on IBS because it’s not all about FODMAPs and it’s definitely not about gluten at all! Some of the clients who consult with me about IBS report that recent dietary changes have triggered or exacerbated gut problems. If the diet in question involves meal replacements, juicing, gluten free or paleo style eating, I immediately think “IBS”. 

Why? Because these dietary approaches can be high in the type of carbohydrate that resist digestion (FODMAPs) or too low in fibre to maintain healthy numbers and variety of gut bacteria. For example, diets that are high in protein and low in carbohydrate can cause constipation, even if the diet is high in vegetables. The gut bacteria simply don’t have enough “food” to survive, and therefore the frequency and quality of bowel motions is compromised.


REASON 8: Ageing

Basically, all of the above factors have more chance of happening to a person over time, and therefore getting older increases IBS risk. It is less the ageing process itself, and more the likelihood of having to take antibiotics, feel more stress, get a gut bug or suffer from an inflammatory condition. The combination and multiplication of these impacting factors over time result in increased IBS risk or symptoms. 

As you can see from the following checklist and diagram, the more contributing factors that you have experienced, the more likely you are to suffer from IBS. While this information does not necessarily help you manage IBS, I hope it provides you with some perspective as to what might have contributed.

• Mum had “tummy troubles” or Dad was “crook in the guts”
• Female gender
• At least one episode of “gastro” or a severe gut bug (eg. food poisoning)
• Ever had/hosted a parasite
• Immune system or chronic inflammation/inflammatory diseases
• Aged over 30 years
• Repeated use of antibiotics
• Stress responses / not coping well with stress / anxiety
• Dietary changes.



(1) Saito, Y. A. (2011). The Role of Genetics in IBS. Gastroenterology Clinics of North America, 40(1), 45–67. http://doi.org/10.1016/j.gtc.2010.12.011

(2) Verdu, E et al Irritable Bowel Syndrome Best Practice & Research Clinical Gastroenterology Vol. 18, No. 2, pp. 315–321, 2004

(3) Paula, H. et al Non-enteric infections, antibiotic use, and risk of development of functional gastrointestinal disorders Neurogastroenterology & Motility epub 2015 Aug 24