All manner of products - cereal, cake mix, pasta, even beer - are making the jump from niche stores to the big supermarkets. Celebrities tout a gluten-free diet as a way to lose weight and feel healthier. Big food manufacturers and supermarkets in Australia and the US are investing heavily.

Gluten is a serious problem for a small group of people, especially those with coeliac disease. Their diets must be free of gluten - a protein found in wheat, barley and rye.

An estimated 1 per cent of Australians and Americans have coeliac disease. For them, and others with gluten sensitivities, the rapid spread of gluten-free food is a godsend.

But for most of the population, there is no proof that a gluten-free diet offers any benefit - and it's costly. For example, a 750-gram pack of gluten-free flour in Australian supermarkets costs up to $6 - two or three times more than normal flour.

Demand for gluten-free products is soaring. Last month, Coles introduced its "Simply Gluten Free" range: more than 40 products, including pasta, pancake mix, muesli, Anzac biscuits, cheese twists, cake mixes and biscuits. Coles says it is responding to strong demand from shoppers.

One reason for the gluten-free boom, market analysts say, is the buzz bestowed by celebrities, such as Gwyneth Paltrow and Oprah Winfrey.

"There are a lot of misconceptions about the gluten-free diet out there," says Whitney Ehret, communications director for America's National Foundation for Coeliac Awareness.

Gluten, an essential component in making cakes fluffy and biscuits chewy, has become demonised. Some products billed as gluten-free contained no gluten to begin with, but marketers want to capitalise on the health halo.

In people with coeliac disease, gluten causes the body to attack itself by destroying "villi", tiny fingerlike protrusions lining the small intestine that are vital for absorbing nutrition.

One per cent of Australians have coeliac disease, but David Sullivan, executive director of Coeliac NSW and ACT, estimates that three-quarters of them are undiagnosed. That means only .25 per cent of Australians are coeliac and know it.

Yet a study conducted by the Coeliac Research Fund in late 2010 showed that about 10 per cent of Australians are either strictly controlling or limiting gluten in their diets. And anecdotally that number appears to be increasing - "as reflected by the significant increase in gluten-free products now available", Sullivan says.

In a US survey by Packaged Facts last year, 20 per cent of consumers said they bought gluten-free products because a member of their household had coeliac disease or was gluten-sensitive. But 46 per cent bought gluten-free (for themselves) for the perceived health benefits. Another 30 per cent said they bought gluten-free to manage weight, and 22 per cent because they believed these were lower in carbohydrates.

The Packaged Facts report notes that neither the weight-management nor the lower-carbs claim is true.

"But consumers tend to think otherwise," Sullivan says.

Yet coeliac disease remains a serious medical condition - one that Sullivan believes is "under-diagnosed" by doctors. That may be because its symptoms vary widely, from mild and non-specific to severe and debilitating.

"Understandably, CD is often not the first consideration when a patient presents with issues such as lethargy and gastrointestinal symptoms. Irritable bowel, gastroenteritis, stress, vitamin and mineral deficiencies and other common health complaints may be treated in isolation and delay a diagnosis of CD," Sullivan says.

At the same time, self-diagnosis is increasing as more information becomes readily accessible through social media, he says.

If unsure about your symptoms or what to do, call Coeliac Australia on 1300 GLUTEN, or visit the website at coeliac.org.au.