In the not so distant past, medical professionals often thought that the bloating and distension frequently reported by their IBS patients were just products of an overly active imagination. If you have had the experience of having to loosen your belt as your day goes by, you know how off base these doctors were. This overview of the current state of the research on bloating and distension in IBS can help you be on the same page with your own medical provider.

Bloating is a fairly universal phenomenon, as it is estimated that 16% to 30% of the general population reports that they suffer from bloating. These numbers skyrocket when talking about IBS patients, with 80% to 90% of patients reporting bloating. Given these numbers, it is somewhat surprising that bloating is not even listed as part of the Rome III criteria for diagnosing IBS.

Bloating is defined as the perception of increased pressure in the abdomen. Bloating is reported more frequently by women than men, but this may be due to differences in how the symptom is perceived by the different genders. Bloating is also more likely to affect patients with constipation-predominant IBS (IBS-C) and mixed type IBS, than those with diarrhea-predominant IBS (IBS-D). This does not mean that bloating doesn’t affect IBS-D patients, in fact, bloating is a problem for almost half of all IBS-D patients.

Distension differs from bloating in that it involves a measurable change in the circumference of the abdomen. Distension typically gets worse as the day wears on. You may also find that your abdomen gets more distended after you have eaten. It is estimated that approximately half of all IBS patients experience distension. Distension and bloating often are experienced simultaneously, but it is thought that they result from different bodily processes.
Causes of Bloating and Distension

Contrary to what you might think, excessive gas is not necessarily the reason behind bloating and distension. Several mechanisms that are being explored as possible contributors to bloating and distension are:

Trapped gas
Visceral hypersensitivity
Impairment of the abdominal wall in responding to pressure

There is also evidence that bloating may be a problem for sub-groups of IBS patients who suffer from:

Carbohydrate intolerances
Bacterial imbalances
Small intestine bacterial overgrowth (SIBO)

Effect on Quality of Life

The symptom of bloating clearly negatively impacts one's quality of life. In surveys, bloating runs neck and neck with abdominal pain as the most severe symptom IBS patients must deal with. Bloating also appears to be the symptom least likely to respond to treatment. The symptom of bloating appears to go beyond just discomfort -- one study found that bloating in IBS patients was related to decreased energy, a decreased level of physical activity, and a lowered of food intake.