• Following on from part one, should you start a gluten-free diet, the next part in the series looks at the symptoms and triggers of coeliac disease.
As thousands of perfectly healthy people ditch gluten in the hope it might help them to lose weight, it seems there are even more for whom gluten really could be a problem, yet who are still tucking in to bread and biscuits completely unaware of the effect this could be having on their health.
For coeliacs, the price of consuming gluten can be very high, affecting their health very badly. Left untreated, coeliac disease can increase the risk of life-limiting conditions such as osteoporosis and - more rarely - certain gut cancers.
Coeliac disease is a lifelong condition in which the gluten molecule triggers a reaction that causes the immune system to attack its own tissue, and the only treatment is going completely gluten-free.
Gluten is a protein found in wheat, barley and rye (and it is present in nearly all bread, cakes and pasta).
The most typical symptoms of coeliac disease are gut problems such as diarrhoea, bloating and abdominal pain, which are caused when the body's immune response damages the gut lining.
This damage often triggers fatigue and anaemia if important nutrients from food are not absorbed sufficiently as a result.
The condition affects about one in 100 people in the UK, but according to the charity Coeliac UK, only 24 per cent of those with the condition have actually been diagnosed.
This means there could be as many as half-a-million people who have coeliac disease, but don't yet know they've got it. One reason for this is that coeliac disease doesn't always cause gut symptoms, but may instead cause damage elsewhere in the body - consequently, coeliac disease is thought to be responsible for all sorts of seemingly unrelated conditions, from infertility to balance issues, mouth ulcers, headaches, 'brain fog' and joint pain.
The vast majority of people who give up gluten don't have, and will never have, coeliac disease. But experts are concerned that some 'lifestyle coeliacs' - people who cut out gluten because it makes them feel better in ways they find difficult to pinpoint - may, in fact, have coeliac disease without knowing it.
"The assumption used to be that if it was coeliac disease, there would always be massive weight loss and gastrointestinal symptoms such as diarrhoea," Sarah Sleet, chief executive of Coeliac UK told the Daily Mail.
"But we now know that people with undiagnosed coeliac disease often don't fit that picture. Instead, they may be suffering an array of symptoms as diverse as problems with dental enamel or mouth ulcers."
Professor David Sanders, a gastroenterologist at the Royal Hallamshire Hospital in Sheffield, says: "The biggest problem with diagnosing coeliac disease is that it's so diverse in how it presents.
"Coeliac disease is usually an adult diagnosis, most commonly between the ages of 30 and 60. However, it is possible that it's there from childhood and we're failing to diagnose it."
Whether or not you have gut symptoms, the one unifying factor seems to be persistent tiredness.
Experts fear that when 'lifestyle coeliacs' with undiagnosed coeliac disease cut back on gluten, even the most obvious coeliac symptoms would be masked.
This would make them less likely to seek diagnosis, which could be bad news for their health.
For although they are cutting back on gluten anyway, which would have a positive impact, coeliacs have to be fastidious about avoiding every tiny trace of gluten (they must be vigilant about hidden gluten in a surprising number of foods) to avoid long-term implications.
How a tummy bug could trigger it
You are not necessarily born with coeliac disease and symptoms but, if you have the genes, it could manifest at any time in your life. There are two specific genes - HLA-DQ2 and DQ8 - that all coeliacs have.
So, too, do 30 per cent of the population, though only 1 per cent have coeliac disease.
As Dr Peter Green, a U.S. coeliac specialist and author of the book Gluten Exposed, explains: "We don't know why only a small percentage of people who are genetically predisposed develop an active form of coeliac disease and why it occurs at varying times in their lives."
However, it seems a combination of gluten, genes and environmental factors such as a tummy bug, over-use of antibiotics or other drugs and even pregnancy are implicated.
Do I need a coeliac disease test?
if you suspect you have coeliac disease or a problem with wheat, don't stop eating gluten.
First, visit the Coeliac UK website (isitcoeliacdisease.org.uk) and fill in their assessment questionnaire.
Then go to your doctor and ask for a blood test.
This looks for an enzyme called IgA, which, in people with coeliac disease, converts the gliadin protein found in gluten into a more toxic molecule. However, IgA is only detectable when a coeliac eats gluten and, for an accurate diagnosis, you have to eat gluten in more than one meal every day for six weeks before testing is done.
If the blood test is positive, the diagnosis will be confirmed with a gut biopsy - where a thin tube is passed into the gut via the mouth and tiny samples are collected from the lining of the small intestine.
A negative result does not mean you don't have coeliac disease, and you may develop it later.
You can get gene testing (available online for around £200), and this may show if you have the coeliac genes (HLA-DQ2 and DQ8), but it cannot indicate whether you have, or ever will have, coeliac disease.
However, Dr Green believes these tests can be useful to determine which family members to screen, or to narrow things down if other tests prove inconclusive.
You can buy home test kits that purport to screen for coeliac disease either over the counter or online for around £15 (about $27 NZD) - these fingerprick blood tests claim to reveal gluten intolerance in ten minutes.
Coeliac UK warns, though, that these cannot provide a coeliac diagnosis and strongly recommends any results - whatever the outcome - are discussed with your GP.
When it comes to diagnosing gluten 'sensitivity', you can get tests for food intolerances from some practitioners online, but Dr Green warns you may end up paying for something that could, in actuality, be "scientifically meaningless".
Some stool tests purport to be able to identify a biological marker for gluten sensitivity but, according to Dr Green, no such marker exists.
Applied kinesiology, the study of muscle movement, which is said to diagnose gluten sensitivity, is also dismissed by many experts, including Dr Green.
He warns that, in general, 'self-testing' could mean you avoid a proper medical evaluation and potentially miss a serious illness.
He adds: "Diarrhoea and pain can be caused by coeliac disease - or they could be a sign of bacterial infection, a virus, food poisoning, acute pancreatitis [inflamed pancreas], as well as a long list of other multi-system disorders."
Why ditching gluten can make you fat
For 'lifestyle' coeliacs who give up gluten in an attempt to slim down, the transition to gluten-free comes with a stark warning: if you switch processed gluten-containing foods for processed gluten-free foods, you are highly unlikely to lose weight. In fact, you could gain pounds.
"If you cut out all bread, pasta, cakes and snacks and don't replace them with gluten-free, you may lose weight," says U.S. coeliac specialist Dr Peter Green. "But if you're coeliac, you might gain weight, as going gluten-free should mean your intestine is healing and you're now able to digest food properly."
Non-coeliacs face weight gain, too, because manufactured gluten-free products very often contain a higher proportion of fat and sugar to compensate for the loss of taste and texture that can come as a result of using gluten-free flours.