When 21-year-old Camilla Chia was crowned Miss Oxford last summer, it marked the end of a lifelong battle with her health.

None of those who voted for her knew that the vibrant, shapely ?student had battled stomach pain and sickness all her life, and had been repeatedly dismissed by the medical profession as neurotic.

But underneath her one-piece swimming costume, the Oxford-based student hid a two-inch scar through the middle of her belly ?button — the result of an operation that, two years ago, turned her life around.

Pain-free: Beauty queen Camilla feared she could never be well after suffering from stomach cramps and being unable to keep food down

Camilla’s childhood was punctuated pain. ‘I don’t remember when my tummy didn’t hurt,’ she says. ‘?Sometimes it would be right in the middle of my abdomen, then at other times high up under my rib cage. ’

She had been a sickly baby, and her mother assumed she was suffering from colic for many years. but things got much worse when she started senior school, at 11.

The episodes of pain — which struck at least twice a week — were so severe she’d be rolled up into a ball in agony for hours. Her only relief was a hot-water bottle. Before long she had burn marks on her stomach from clutching it so tightly for such long periods of time.

Doctors were baffled. Camilla was tested for parasites (they’d been on a family holiday to Malaysia, so it was considered a possible cause), treated for irritable bowel syndrome and sent home once with a course of drugs to treat what was thought to be ‘stomach migraine’.

Nothing worked. And by the age of 14 the attacks were joined by ?frequent bouts of violent sickness.

‘The really debilitating thing was the fact that there was no pattern to the episodes,’ says Camilla. ‘So I never knew when the pain would come, or when I’d be extremely sick.’

She had to take a lot of time off school, and missed out on much of the fun, social side of her teenage years. ‘Each time I was sick the pain would ease for a few minutes, then it would build, and I’d be sick again. This would happen three or four times in a row, lasting half a day and right through the night.’

Unable to keep food down, Camilla lost a lot of weight. At her lowest, she dropped to five-and-a-half stone (she’s 5ft 7in tall) and her periods stopped.

Her GP became ?convinced she was anorexic. but her mother refused to accept the diagnosis and continued to research ?possible causes for Camilla’s pain, repeatedly begging the GP for help.

‘Each time we went I would be weaker and more exhausted than the last, so Mum would have to do all the talking, and they soon started to think she was neurotic, too.’

In full health: Camilla had an operation to untwist her gut meaning she could put on some weight on her skinny frame and prove she didn’t have an eating disorder

At 16, Camilla hit rock-bottom when a protracted bout of pain and sickness lasted for three weeks. ‘I was so weak I couldn’t get out of bed,’ she says,

‘I remember feeling so bad that I turned off my mobile phone — something a teenager would never do — because I couldn’t stand the noise of it ringing and felt just too wretched to talk to anyone.’

Finally, she collapsed, and her mother called an ambulance. She spent two weeks at the John Radcliffe Hospital, much of the time on a drip, and ?underwent a battery of tests.

She was finally sent home with anti-nausea drugs (Motilium) which calmed her symptoms and the attacks dropped from two or three per week to about one a month.

Over the next year she was able to gain a little weight, and the barrage of tests continued. Gradually, the doctors started to think her symptoms might have a physical rather than a psychological cause and told Camilla they were considering the possibility that her gut might be twisting and then untwisting itself.

Then, just before her 18th birthday, she had a CT scan to check whether food was passing properly through her gut.

There was a buzz of excitement in the scanning room and Camilla was ushered in front of Professor Neil Mortensen, clinical director of surgery, to hear the words she never thought she’d hear: ‘We’ve found out what’s wrong with you.’

Prof Mortensen explained she had a ‘malrotation of the gut’ where the small intestine becomes twisted at the point it meets the large intestine.

‘Malrotation happens in the womb,’ he explains. ‘as the ?foetus is developing, the gut grows in length, flopping from side to side as it folds itself inside the abdomen. For some reason, part of Camilla’s gut flopped to the right instead of the left, twisting the bowel.’

In some people, twists like this cause no problems.

But for others, like Camilla, the bowel exists in a ‘subcritical’ state, working normally until you eat something fibrous, which creates a blockage at the point of the twist.

‘This can be extremely painful and potentially dangerous,’ says Prof Mortensen, ‘if the blood supply to the gut is reduced, that section can die, and if it’s not caught quickly, the condition can be fatal.’

Malrotation is rare. Prof Mortensen says he’d only expect to see one or two cases in his career, usually in very young children. And it is very ?difficult to diagnose.

‘we see many teenagers with tummy pains which can have all sorts of physical and psychological triggers,’ he says.

‘Symptoms like Camilla’s can very often be down to some kind of psychological problem — such as anorexia — growing pains or even Crohn’s disease (an inflammatory condition). certainly in Camilla’s case, it took a while for the penny to drop.’

An operation was booked and Camilla was warned she would have a five to six-inch scar across her tummy.

‘Bizarrely, considering how much pain and discomfort I’d been through for so long, I found myself briefly worrying about the scar,’ she says.

‘but the thought of living life with no pain and no sickness was something I hadn’t ever allowed myself to even dream about, so I knew this procedure would change my life.’

During a one-and-a-half-hour operation, Prof Mortensen and his team made an incision below Camilla’s belly button and searched for the place where the bowel was twisted.

‘in Camilla’s case it was very obvious,’ he says. ‘Her gut had twisted 360 degrees into a kind of spiral, which was being held in place by spider’s web-like adhesions.’

The team were able to cut the threads holding her bowel in the wrong ?position, untwist it, and let it fall properly into place.

‘sometimes you have to glue or suture [stitch] the bowel into the correct position in the ?stomach cavity but we were confident in Camilla’s case, that it would stay where it should,’ says Prof Mortensen.

Waking up from the operation, Camilla was thrilled to see the scar was only two inches long. And after a few days on fluids, Camilla recovered quickly and started to gain weight.

Now she is a slim, fit, eight-and-a-half stone.

She says that although her stomach muscles are really strong, her digestive system is still a little sensitive.

‘I get bad stomach aches if I eat lots of processed foods, and I can’t use the Power Plate at the gym because the strong vibrations seem to shake everything around,’ she says.

In 2009, a friend at her gym put her name forward for a beauty contest, and she was crowned Miss Oxford last summer.

‘I still get emotional when I think about my teenage years,’ she says. ‘it was desperately difficult ?living with the prospect of always being sick and no one ever knowing what was wrong with me.

‘I certainly never thought I would end up competing in a beauty contest!’