Irritable Bowel Syndrome Symptoms

Irritable bowel syndrome is thought to be a disorder of the ‘gut-brain’ axis, which is a complex two-way system of communication between the gastrointestinal (GI) tract and the brain.

While IBS is usually a long-term disorder, symptoms come and go and vary in severity. IBS develops more frequently in younger women, although it can also affect men and older age groups. The most common risk factor for developing IBS is acute infection (e.g. food poisoning). However, diet, psychological stress, and anxiety, have also been linked to the condition.

IBS is a highly complex syndrome, but the underlying mechanisms behind it likely involve the following:

Disordered gut motility – Gut motility is the term given to the stretching and contractions of the muscles in the gastrointestinal (GI) tract. These movements enable food to move along the digestive tract while absorption of nutrients takes place.

Symptoms of IBS have been linked to changes in gut motility. This is because repetitive gut contractions can give rise to abdominal pain, and changes in ‘transit’ speed. These changes can result in constipation or diarrhoea as well.

There are two main types of IBS. Contractions that are faster than normal are common in people with IBS-D (IBS that causes diarrhoea), while contractions that are too slow are more common in people with IBS-C (IBS that leads to constipation). There is also IBS-M, which is when people experience a combination of IBS-D and IBS-C.

Visceral hypersensitivity – People with IBS tend to be especially sensitive to stimuli arising from the gut. This may occur when there is a build-up of pressure (e.g. gas production) or sensations of pain.

Changes in the nervous system – The nervous system helps control gut motility, sensation, lining (or barrier) mechanisms, and gut secretions. Changes can occur to any of these if the nervous system is influenced by factors such as stress, anxiety, or gastrointestinal infection.

Factors which impact on the above, include:

Genetics – Genetic changes may influence muscles or nerves relating to the GI tract.

Diet – Some foods contain high amounts of FODMAPS (fermentable oligosaccharides, disaccharides, monosaccharides and polyols). These foods include green vegetables, legumes, and sorbitol, and can be difficult to digest. They also appear to trigger symptoms in people with IBS, causing diarrhoea or excess gas.

Microbiome – Changes to the microbiome (the ‘good’ bacteria that normally live in the gut) can also contribute to IBS symptoms. While more research is needed, studies suggest that acute infection and antibiotic therapy can alter the makeup of the microbiome, giving rise to IBS symptoms.

Changes to barrier function – The gut wall acts as a selective barrier between the gut lumen and the rest of the body. If the gut wall is damaged (e.g. by infection), the immune system may release chemicals which can affect gut motility, sensation, and secretion. Long-term inflammation may also occur.

Psychological influencers – While some people with IBS can remain psychologically unaffected by the condition, stress, anxiety, and strong emotional responses can aggravate symptoms of IBS.