If you start the day with a flat belly but feel bloated by bedtime, there's a good chance you're a woman.
Why being female makes you more bloat-prone isn't clear, but shifting hormones could play a part.
Women surveyed by Australia's Gut Foundation, which specialises in research into digestive problems, reported that bloating was more common before a period.
Almost as big a problem as bloating itself is that its symptoms are sometimes disregarded by doctors or lumped under the heading of Irritable Bowel Syndrome.
This means the real cause may not be found and treated, says Terry Bolin, an associate professor of medicine at the University of NSW and gastroenterologist.
''Some women who have problems with bloating also mistakenly assume they're overweight and go on restrictive diets,'' Bolin says. ''This can make bloating worse if it's caused by constipation and they then reduce their fibre intake.''
While constipation is a common cause of bloating, it's only one of many possibilities unravelled in Bolin's new book, Understanding Gas and Bloating: Why Can't I Do Up My Jeans at Night?
Food intolerance, lactose intolerance and coeliac disease can be underlying causes, as can excess gas generated by some sugars in food, including fructose, fructans and sorbitol.
But it can also be a problem with the muscular contractions in the small intestine.
In a well-behaved gut, regular muscular contractions keep gas moving smoothly through your system, but sometimes things go wrong. Contractions can be disrupted, trapping pockets of gas and causing bloat.
In some people, the muscles in the gut wall become more elastic and easily blown up with gas - and humans do make lots of the stuff. On average we produce about 25 litres daily, most of which the body reabsorbs.
Even so, the small intestine could be carrying up to three litres of gas at any point in time - the equivalent of two party balloons. If things aren't working well and gas becomes trapped, there can be pain and swelling.
A number of things can disrupt the muscular contractions of the gut. Changing hormone levels before menstruation may be one. Fat and stress are others.
''Studies have shown that if you trickle fat into the small intestine, it can trigger disordered contractions in some people. Any type of fat will do this, whether it's extra virgin olive oil or from KFC,'' Bolin says.
With stress, the problem seems to lie with the complex connections between the brain and nerves in the gut that can affect muscular contraction, especially in people with IBS.
For some people, a tiny dose of tricyclic antidepressants - well below the normal dosage for depression - can help, Bolin says.
What helps prevent or improve bloating? It depends on the cause. Finding that can involve trial and error and expert help from a gastroenterologist and possibly a dietitian.
If the problem is constipation, increasing the fibre in your diet is a solution but it's important to do this gradually. Too much too soon can make the problem worse.
Being physically active is good - it improves the movement of gut muscles. Probiotics can help, too, but it's not clear yet which strains work best, Bolin says, although the following are showing promise: bifidobacterum infantus, lactobacillus acidophilus, lactobacillus casei GG, bifidobacteria animalis lactis (HN019) and lactobacillus plantarum.
''But you can't always rely on one single thing to improve bloating,'' he says. ''You may need more than one approach.''
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