Monday 17 November 2014

Gluten-free diets: Separating wheat from the chaff

By Andy Ho Senior Writer, the Sunday Times, 16 Nov 2014

The Economist magazine recently highlighted how market demand for gluten-free food is growing so fast it is outstripping vegetarian fare. Gluten-free products are projected to be a US$15 billion (S$19.5 billion) sector by 2016, which would make it 50 per cent larger than it was last year. In Singapore, grocers in upmarket malls and expensive sandwich shops are already touting gluten-free menus.

The Latin word for "glue", gluten is the protein that makes dough elastic and enables it to rise. It is found in wheat, barley and rye, so food made from them has gluten, including bread, cakes, breakfast cereals, pasta, beer, some sauces and ready-to-eat meals.

Gluten is the culprit in coeliac disease, a rare but serious condition in which the immune system wrongly identifies it as a threat, and attacks it. If food with gluten is being digested in the small intestines, this attack damages the gut's inner lining, rendering it unable to absorb nutrients.

So coeliacs must keep a gluten-free diet for life. Their diagnosis can be made with certainty as there are biomarkers for it.

But the present gluten-free fad involves non-coeliacs who claim that gluten causes in them the same symptoms that coeliacs have.

These include everything from very smelly diarrhoea and wind to bloating and tummy aches, weight loss, malnutrition, lethargy and retarded growth in childhood.

These non-coeliacs feel that a gluten-free diet improves their symptoms but there is not enough scientific evidence to show if this is true.

In April 2011, a Monash University study published in the Journal of Gastroenterology and Hepatology suggested that gluten may cause those symptoms in some non-coeliacs. It felt that the condition now called "non-coeliac gluten sensitivity" does indeed exist.

This diagnosis in persons who say they develop such symptoms with gluten depends on making sure that they don't actually have coeliac disease as well as an allergy to wheat, two conditions for which there are well-characterised biomarkers. As there are no biomarkers for gluten sensitivity, its diagnosis cannot be made except by exclusion in this way.

The Monash study involved only 34 patients but it was randomised, placebo controlled and double blinded (where both test subjects and researchers don't know which treatment is being given to the participants by a third-party administrator). As this is the gold standard of therapeutic trials, this small study gave the notion of gluten sensitivity a scientific imprimatur of sorts.

Admirably, the Monash group later published a follow-up study that overturned their original one.

They wondered if dietary factors other than gluten which they had not excluded in their first study might be responsible for the symptoms instead.

The most important of these factors are "fodmaps" - poorly absorbed carbohydrates that gut bacteria ferment, producing wind. Fodmap stands for "fermentable oligosaccharides, disaccharides, monosaccharides and polyols", and some examples are fructans in bananas, garlic or onions; galactans in beans; fructose in soft drinks; and lactose in milk.

In the new study, 37 non-coeliacs who thought themselves to be gluten sensitive were put through cycles of high-gluten, low-gluten, and no-gluten diets in which fodmaps were meticulously excluded. Every meal was provided during the trial, where the subjects weren't allowed to know which diet they were being given at any one time.

In the study, all three diets managed to aggravate the symptoms equally. That is, people who believed they were gluten sensitive developed symptoms even when they consumed no gluten.

These people pessimistically expected the test diets to worsen their symptoms, which they did. This is called the "nocebo" response, where symptoms worsen even when one is given an inert dummy or placebo, which was the no-gluten diet in this case.

In Latin, "nocebo" means "I shall harm" whereas "placebo" - like a sugar pill - means "I shall please". The nocebo response has also been demonstrated in people who believe cellphones and wireless Internet make them ill.

The second Monash study, published in The American Gastroenterological Association's journal Gastroenterology in August last year, concluded: "In contrast to our first study… we could find absolutely no specific response to gluten."

It did not quite call gluten sensitivity a myth, since the study was not big enough to have the statistical power to draw such a definitive conclusion. It only found that "gluten may not be a specific trigger of symptoms once dietary fodmaps are reduced".

Not every expert is convinced that gluten sensitivity actually exists as a discrete condition since it has no biomarkers. In December last year, a review published in the journal Current Allergy and Asthma Reports concluded: "On current evidence, (gluten sensitivity's) existence remains unsubstantiated."

What is needed is more and much larger randomised, placebo controlled and double blinded studies, the most rigorous of therapeutic trials with humans.

But there are few such studies because good dietary studies are difficult to execute compared to drug trials, where subjects just have to pop a pill or two once or twice daily, say. By contrast, few people will tolerate being subjected to having every meal decided for them for a month, say.

Coeliac disease is very uncommon among the three main races in Singapore but afflicts up to 1 per cent of Caucasian populations. However, a large Australian survey published in the journal Public Health Nutrition earlier this year found 7 per cent of non-coeliacs identifying themselves as gluten sensitive.

The diagnosis cannot be established with any certainty, so no one knows its real prevalence, if it is indeed a genuine disease.

But now that many have sworn off gluten because they feel better when they do, the gluten-free sector - whose expensive products substitute potato, corn or tapioca starches for wheat flour - will likely continue to flourish. Even if it all turns out to be a myth.

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