The cause of IBS is still unknown. Some experts think IBS is a Motility Disorder.  A hyperactive or oversensitive gut is another possible cause of IBS. and the gut will react to changes influenced by stress, food and hormones.

With the typical chaotic bowel habit of IBS, it is not surprising that it is thought of as a motility disorder. There is an abnormality in the transit time of ingested food.

Sometimes it is slower than normal causing constipation and other times it is faster causing diarrhoea. IBS is generally divided into two groups, constipation predominant and diarrhoea predominant. Some have diarrhoea and constipation alternating. Stools in IBS can vary from watery and unformed to hard pellets.

Some say there is a link between diet and IBS.
Certain foods will trigger IBS symptoms. Intestinal gut activity is stimulated by ingesting food. This is the Gastro-Colic reflex and develops in response to food entering the stomach. In IBS, large meals, fatty meals or just the wrong meal can trigger a very strong gastro colic reflex. This strong gut contraction can cause abdominal pains and or diarrhoea.

There is no evidence that food causes IBS but certain foods and the volume consumed at one time can trigger symptoms.

One suggestion is that the fault that results in IBS resides in the Nervous System. The Enteric Nervous System is a complex interconnection of brain cells in the gut. To understand IBS, experts think you need to understand how the Enteric Nervous System works.

The highest level of serotonin, a neuro-chemical is found in the gut. Significant research is currently done on the chemical and its role in IBS.

Contractions of the smooth muscles of the gut are affected by serotonin. High serotonin levels are found in diarrhoea and low levels in constipation.

Psychological factors such as anxiety, stress and depression can affect the gut. Trauma suc h as physical, sexual and emotional abuse can affect the gut. In IBS, records show a higher incidence of such trauma. Addressing these issues may produce better long term results.

Gastroenteritis as a cause of IBS: IBS can develop is 20-30% of cases of severe gastro-enteritis. Escherichia coli, Salmonella shigella and Camplobacter jejuni are the most common organisms involved. Serotonin levels in gastro-enteritis is very high and in cases that develop IBS this high level continues.

In some women, symptoms fluctuate during the menstrual cycle. The two hormones that control the menstrual cycle are oestrogen and progesterone. The passage of food residue along the large gut is affected by the female hormones.

Yeast according to Prof. Jonathan Bostoff of The Meddlesex Hospital could be a possible cause of IBS. An overgrowth of Candida occurs when there is reduced levels of good bacteria, Lactobacilli and Bifidobactreia.