SINGAPORE- Air is swallowed as we eat and drink throughout the day, which results in the abdomen distending mildly by a few centimetres.
This air is then passed out as flatus (wind) throughout the day and during sleep, so the distension resolves within the day.
Dr Yap Chin Kong, a senior consultant gastroenterologist at Mount Elizabeth Medical Centre, said this passage of air through the gut is silent, apart from flatulence, which is sometimes audible.
For some people, this same "cycling" of air results in rumbling sounds and a greater degree of distension, sometimes to the extent of appearing "pregnant" or giving rise to discomfort or pain.
Such abdominal distension, which occurs suddenly but resolves slowly, is not due to a sudden accumulation of gas, but attributed to a relaxation of the muscles of the abdominal wall, a nervous reflex whose trigger is not known, Dr Yap said. The combination of discomfort, pain and visible distension is then known as abdominal bloating.
Abdominal bloating is also a characteristic of functional bowel disorders, which are diseases of the bowel that are not due to an obvious structural cause.
For instance, diarrhoea, triggered by a viral or bacterial infection, can cause abdominal bloating.
There may be microscopic inflammation in the bowel because of the infection, which sensitises the nerves, Dr Yap said.
"This means the person becomes more sensitive when the bowel is stretched by gas, when previously, the same amount of gas would pass unnoticed," he explained.
Psychological stress can also make the bowel more sensitive to being stretched, which is why patients need assurance to avoid undue anxiety and worsening of their symptoms, he added.
He estimates between 10 and 30 per cent of the population will suffer from abdominal bloating at some point in their lives.
In other cases, he said, bloating can be caused by the consumption of food which increases the production of gas in the intestines, such as legumes, which include beans and daal (spiced lentils).
That is why doctors generally advise patients with abdominal bloating to follow a low Fodmap (fermentable, oligo-, di- and mono-saccharides and polyols) diet, which eliminates highly fermentable types of food, such as honey, wheat, apples, pears, stone fruits (including plums and peaches), onions and artichokes.
Dr Yap said the sugar in these types of food is fermented by gut bacteria and results in increased gas and fluid production.
Not all patients respond to this diet, but doctors cannot predict who will benefit from it, he added.
He said his concern with herbal remedies is the lack of rigorous testing on their safety and efficacy, so people should exercise caution and adopt a "buyer beware" attitude when using these herbs.
He said an easy remedy for someone with abdominal bloating is to lie down so air in the bowel levels off, making it easier to be passed out as flatus.
Anyone who has abdominal bloating for more than two weeks should seek medical help.
Doctors may need to perform tests, such as a stool examination, blood tests, ultrasound scans and gastroscopy or colonoscopy, to rule out serious diseases that can mimic abdominal bloating, Dr Yap said.
These diseases include acid reflux (when acid from the stomach keeps passing back up the food pipe), stomach ulcer, gallbladder stones, inflammatory bowel disease (chronic inflammation of the digestive tract) and some types of cancer.
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