Australasian Science: Australia's authority on science since 1938

Going Gluten-Free: Only for Coeliac Disease?

Going Gluten-Free: Only for Coeliac Disease?

By Michael Potter

Dietary trials have revealed that most people who associate gluten with intestinal discomfort do not have a reliable and reproducible response to gluten ingestion, and may even be harming their health by going on a gluten-free diet.

Wheat is central to the modern diet. Wheat crops cover hundreds of millions of acres of arable land, and wheat provides one-fifth of the world’s intake of calories. A revolution in agricultural practices, including the development of high-yield varieties of wheat at the start of the 20th century, saw an increase in grain production that has helped fuel a population boom; the world’s population has increased fivefold in the past 100 years.

Wheat contains gluten, which is the predominant storage protein in the grain. Gluten’s viscoelastic properties allow it to act as a binding agent, and this is what makes wheat so valuable in cooking.

Gluten, however, is responsible for coeliac disease. The disease, characterised by gastrointestinal symptoms and mal­absorption, was recognised as early as the first century AD, but the link to gluten was only uncovered in the middle of the last century by a Dutch paediatrician named Willem Dicke. He had previously put forward the idea that certain grains, in particular wheat, were responsible for coeliac disease, but was able to verify this theory with observations of children during the Dutch famine of the Second World War. The symptoms of these children improved with the bread shortages during wartime, only to have their condition deteriorate when the famine ended and bread was reintroduced to their diet. Since then we have learned a great deal more about the condition.

Coeliac disease is an auto-immune disease in which the ingestion of gluten triggers a response that results in small intestinal damage While the condition has a strong genetic predisposition, most people in the community with the genes that allow development of coeliac disease (as many as 55% of people in Australia) never develop the condition.

Because of this wayward inflammatory response, the small bowel is damaged. In fact, the delicate microstructure of the duodenum – the first part of the small bowel, which is responsible for the absorption of vital nutrients from the diet – can be completely flattened. Consequently, patients with coeliac disease suffer from a range of symptoms, including abdominal discomfort and diarrhoea, vitamin deficiencies from malabsorption, and even a marginally higher rate of small bowel malignancies, all as a consequence of this chronic gastrointestinal inflammation.

Coeliac disease used to be a rare condition, but with improved diagnostic tests, as well as increasing awareness of the disease in the medical community, many more people are being diagnosed and benefiting from treatment with a gluten-free diet. These days, coeliac disease is relatively common, and believed to affect approximately 1% of the Australian population, almost all of whom will go on to lead a normal, healthy life after excluding gluten from their diet.

In addition to those in the population who have a diagnosis of coeliac disease is an even greater number of people who attribute gastrointestinal symptoms to the ingestion of gluten-containing food, and subsequently limit their intake of gluten or avoid it completely. Studies from around the world have shown the rate of self-reported gluten or wheat sensitivity is 7–13%. Recent research from the US has shown that the number of people putting themselves onto a gluten-free diet is increasing even though the prevalence of coeliac disease has stabilised.

This has led researchers to investigate a condition known as “non-coeliac gluten or wheat sensitivity”. Sufferers from this condition do not have coeliac disease or traditional wheat allergy – in fact, they have had these conditions ruled out through extensive testing – but they do have symptoms that respond to a gluten-free diet and recur if gluten is reintroduced in a blinded, placebo-controlled dietary experiment. In these experiments they are given gluten and then placebo, or vice-versa, over a period of a month without knowing what they are eating, and their symptoms are carefully evaluated. Only those whose symptoms recur with gluten, but not with the placebo, are labelled as having non-coeliac gluten sensitivity.

Those eventually diagnosed with this new condition exhibit subtle inflammation in their small intestine, but not to the same degree as in coeliac disease. Supporting the notion that it is a distinct disease separate from coeliac disease, it is characterised by a different immunological signature, and many do not have the characteristic coeliac disease gene profile.

A wide range of symptoms have been attributed to non-coeliac gluten or wheat sensitivity, including gastrointestinal symptoms such as abdominal pain, diarrhoea, bloating and early satiety. Other non-gastrointestinal symptoms are also implicated, including tiredness, lack of well-being, headache, anxiety, joint and muscle pains, and skin rashes. This means that gluten or wheat may be implicated in a wide range of chronic physical complaints.

Unfortunately, however, most people who associate gluten with chronic gastrointestinal or other symptoms (i.e. the 4–13% of the population who self-report gluten sensitivity) do not demonstrate a reliable and reproducible response to gluten ingestion in these controlled dietary trials. Only 16% of people who are put through this process will have proven non-coeliac gluten or wheat sensitivity. This does not mean that these people are imagining their symptoms, but rather that their symptoms are unlikely to be caused by gluten, and therefore avoiding gluten is not the answer.

For people whose symptoms are not caused by gluten, a gluten-free diet may in fact be harmful. Research has demonstrated that a gluten-free diet may be deficient in several vitamins and micronutrients, and negatively affect cardiovascular risk factors such as cholesterol levels and body mass index. It is also costly, with gluten-free products costing significantly more than their gluten-containing equivalents. There is no question about the benefits for patients with coeliac disease, but just as we would not think to take anti-hypertensive medication if we had normal blood pressure, we should think twice before pursuing a gluten-free diet with no firm indication.

With research into non-coeliac gluten or wheat sensitivity only in its infancy, we do not have any practical diagnostic tests or procedures we can use to identify who has non-coeliac gluten sensitivity. Even if only a small portion of gluten avoiders are truly gluten-sensitive, this equates to a considerable number of people in the community who may benefit symptomatically from gluten avoidance or exclusion. The evidence we have to date, however, suggests that the majority of wheat avoiders are incorrectly attributing a number of symptoms to the ingestion of gluten, and subjecting themselves unnecessarily to a costly, inconvenient and potentially unhealthy diet.

Further research into non-coeliac gluten sensitivity will ideally lead to the development of better testing strategies that will allow us to identify who will, and who will not, benefit from a gluten-free diet.

Dr Michael Potter is Conjoint Research Fellow at The University of Newcastle, and Gastroenterology Registrar at John Hunter Hospital, Newcastle.