Oats in the gluten-free diet

The issue of whether oats can be included safely in the coeliac diet remains controversial. Alex Gazzola examines the current evidence and recommendations.

The humble oat is a species of cereal grown for its seed – a ‘cousin’ to the wheat, barley and rye ‘siblings’ – and which is consumed as oatmeal, rolled oats or as oat flour. The controversy concerning its inclusion in the gluten-free diet (GFD) has been rumbling for several decades, albeit perhaps less so in recent years, during which time a number of studies have shown oats to be safe – at least in moderate portions for the large majority of those with coeliac disease.

Nutritionally, oats have much going for them. They are rich in iron, magnesium, B vitamins and soluble fibre – which a GFD can sometimes be deficient in. Further, they are high in protein and low in saturated fat. The consumption of beta glucans – a form of the soluble fibre found in oats – can reduce LDL (‘bad’) cholesterol and total cholesterol levels, helping cardiovascular health, as well as boost immune system function. Blessed with low glycaemic index (GI) values, they stabilise blood sugar levels – important for coeliacs who are also diabetics.

It’s understandable, then, why natural charity Coeliac UK are keen to reassure coeliacs about their safety, and why free-from manufacturers are increasingly developing gluten-free oat-based products, such as mueslis, oatcakes and biscuits. Oats are affordable, tasty, add variety to an already restricted diet, and a lot of coeliacs enjoy them.

Nevertheless, question marks remain, and with difference in opinion and advice on an international level, among experts, coeliac organisations and coeliacs themselves, it remains a topic of concern.

The official line
Coeliac UK say that most coeliacs can tolerate avenin – the protein unique to oats and analogous to gliadin in wheat, secalin in rye and hordein in barley which go under the collective name of ‘gluten’.

The issue with most commerically produced oats is cross-contamination with wheat or barley flours at some stage during the harvesting, milling or packaging process, which renders these oats and foods produced from them unsafe (oat flour can be as much as 15% wheat flour). It is not enough that such oats are labelled ‘pure oats’ or ‘100% oats’ – these can still carry wheat-flour contamination – and coeliacs who consume or wish to consume oat-based products should insist on ‘gluten free’ labelling.

For non-symptomatic coeliacs established on a GFD and wishing to reintroduce oats, the advice is to only do so under the care and monitoring of your healthcare team, who can help check for any deterioration to health or blood-test results during regular follow-ups.

For newly diagnosed coeliacs, Coeliac UK advise waiting six to twelve months, until symptoms have improved, and a ‘baseline’ of steady health has been achieved, before oat introduction is considered, again under the care of your GP or dietitian. They say: “In cases where the introduction of oats into the diet appears to result in development of symptoms the British Society of Gastroenterology advise it may be worth considering a repeat duodenal biopsy to ensure histological remission.” The recommendations from Coeliac Ireland are broadly the same.

But is the evidence to support this position strong and reliable enough?

Supporting studies
Much of the pro-oat research hails from Scandinavia – a key producer of oats.

Scientists from the Kuopio University Hospital in Finland concluded in their 1995 study published in the New England Journal of Medicine that “moderate amounts of oats” can be safely included in the GFD, and these were supported by their subsequent 2002 study published in Gut, which was the first longer-term (five-year) study.

A 2003 report, again published in Gut, and this from Norwegian researchers, found that 18 of 19 coeliacs challenged with oats could tolerate them (95%) – although they did induce villous atrophy in one.

A subsequent double-blind placebo-controlled study from Norrköping Hospital, Sweden, published in Gut in 2004, demonstrated that, again, “moderate amounts of oats” do not prevent clinical or small bowel mucosal healing.

A Norwegian study, published in 2008 in the Scandinavian Journal of Gastroenterology by researchers at the Akershus University College, Lillestrøm, found that including oats in the diet did not increase levels of anti-avenin antibodies (IgA) in coeliac patients established on a GFD.

On the other hand …
Although these and other studies – and a number of subsequent reviews of the studies – appear to support the cautious inclusion of oats in the GFD, some considerations must be borne in mind.

Not all studies involved biopsies, and blood tests to detect coeliac antibodies may not accurately reflect the true picture of intolerance where oats are concerned. Many studies involved small numbers of participants, and it is possible that potential study volunteers who already believed themselves sensitive to oats may have been less likely to put themselves forward during the studies’ recruitment processes, skewing the actual picture. The 1995 Finnish study had a high withdrawal rate of over 10%, many of which could potentially have been due to symptomatic relapse.

Importantly, other than the five-year Swedish study, we don’t have much in the way of long-term studies to reassure us. Further, we know that pure oat avenins can induce reactions. This 2004 study published in PLoS Medicine, which examined a small group of patients with both apparent tolerance of oats and with clinical symptoms on an oat-containing diet, concluded that some coeliac patients “have avenin-reactive mucosal T-cells that can cause mucosal inflammation” and that “oat intolerance may be a reason for villous atrophy and inflammation in patients with celiac disease who are eating oats but otherwise are adhering to a strict gluten-free diet.”

Not all oats are equal …
One of the most interesting areas of more recent search centres on different breeds of oats and their varying reactive potential. This small Italian study from 2007 found that four different cultivars of oats all elicited responses from the lymphocytes (blood cells) of ten coeliac children – but to differing degrees. In another paper later that year, the same team from Rome revealed, via a form of in-vitro assay testing, that some varieties of oats could be harmful, and warned that “constant, small amounts of … certain avenins, may prevent complete recovery of the intestinal mucosa”.

This should not come as a surprise. We know that varieties of wheat, including spelt, can vary in their gliadin content (contrary to widespread belief, types of spelt can contain more gluten than other forms of wheat) and that different types of barley exhibit similar variety. Oat varieties are now being analysed more closely, and the results are introducing new ideas to the debate about oats in the GFD.

This began in earnest with a Spanish study published in February 2011 in Gut, which found that of nine cultivars of oat, three varieties demonstrated considerable cross-reactivity with the main coeliac antibody that is reactive against the key toxic 33-mer peptide, three demonstrated ‘slight reactivity’, and three demonstrated ‘no detectable reactivity’.

These results questioned the prevailing view that, as the Spanish researchers put it, “pure oats are safe for most people with CD, and contamination with other cereal sources is the main problem facing people”. They pointed out that the types of oats used in earlier studies on which the recommendations are based, their levels of purity, and the designs of the studies themselves, including the recruitment and numbers of participants, “have not allowed a clear answer as to whether oats are safe or not”. The types and purities of differing commercially available oats may also account for coeliac patients’ widely disparate experiences with the grain.

Arguably the most important finding was that some cultivars of oats are completely non-reactive in their pure state. Did this, as the researchers claim, “open up a means to identify immunologically safe oat cultivars, which could be used to enrich a GFD”? It is worth adding that gliadin (from wheat) was found to be 40 to 400 times more reactive than even the most toxic avenin from oats, and that this would roughly correspond to a tolerance level in the range of 2-20g per day of the most reactive oat variety.

The theme continued with this Italian study published in the Journal of Cereal Science in July 2011, which examined 36 oat varieties, and found “most samples” came in at under 20ppm of cross-reactive avenin, but some contained 80ppm or more. Given we believe that 10mg of gluten daily is safe for the vast majority of coeliacs, this would correspond with a maximum of around 125g of gluten-free oats a day as safe – assuming no other trace gluten ingestion through other sources, which of course is unlikely.

The bigger picture here is that we may be better off thinking of oat tolerance (or intolerance) as a spectrum, not as a black or white scenario. It may not be the case that 95% of coeliacs are OK with oats and 5% are not. Instead, all coeliacs may have a measurable tolerance level, but those individual tolerance levels could vary considerably.

Australian gastroenterologist Dr Robert Anderson – a coeliac researcher known especially for his work on the coeliac vaccine – believes the figure of oat-sensitive coeliacs is closer to 20% than 5%. This is based on studies with his colleagues at the Walter and Eliza Hall Institute of Medical Research, Victoria, that found T-cell activation by avenin in 5 out of 23 individuals consuming a considerable 100g oats per day. But this would be in line with the theory of a ‘sliding scale’ of tolerance thresholds among coeliacs with increased oat intake – that approaching 100% can tolerate 2g, that 95% can tolerate 50g, and that Anderson’s 80% can tolerate 100g.

It is perhaps not surprising that no oat product can be labelled gluten free in Australia and New Zealand – nations renowned for their stricter ‘no detectable gluten’ (ie 3-5ppm) rules defining gluten-free foods – and that Coeliac Australia’s advice is that “despite the extensive medical research done in relation to oats and coeliac disease, oats should be excluded from a gluten free diet until the research is more conclusive and definitive …”

The way forward
The only thing which is clear, then, is that the picture is not clear.

The most recent study, from Ireland, changes little. It was published in Clinical and Experimental Immunology in March 2013 and revealed that 95% of tissue samples from 46 coeliacs who consumed an average of almost 300g gluten-free oats per week for a year either did not worsen or showed signs of improvement.

Coeliac UK acknowledge that many coeliacs do not wish to consume or reintroduce oats, and research by Nairn’s conducted on Coeliac UK members suggests 28% of coeliacs don’t eat oats and 33% only eat oats or oat-based foods occasionally. 

The charity refers individuals to their healthcare team for specific advice. They point out that although 50g is often-quoted as a tolerable daily portion, there is no specific recommendation regarding this, and the figure only stems from an average used in the key oat studies. (By comparison, The Canadian Celiac Association puts a safe figure of 50-70g of gluten-free oats for adults, and 20-25g for children.) Measuring intake of oats for porridge is not difficult for any owner of kitchen scales, but now that GF oats are increasingly being used in processed free-from foods in the form of biscuits and snack bars, calculations might become trickier.

According to current labelling legislation, oats are considered a gluten grain, and must be declared. Look for ‘gluten free’ confirmation on the product: this over-rides any precautionary ‘contains oat gluten’ statement in any allergen box. All oat products listed in Coeliac UK’s Food and Drink Directory are from uncontaminated sources. Some brands may also be found via our FreeFrom Food Directories – see a selection below.

The key is to not experiment alone. An oat-containing diet will typically be higher in fibre than an oat-free GF diet, which can result in bowel symptoms (wind, bloating, changes in regularity) manifesting themselves while your system adjusts. Initially, it may be difficult to ascertain whether these are innocent or coeliac-related. A review from Lincoln County Hospital on oat safety concluded that coeliacs should “stop eating oats if they develop any symptoms” on reintroduction – but this is perhaps over-cautious. A dietitian can best advise, and it’s important to take more fluids along with your oats. Apprehension concerning consuming oats can manifest itself with mild bowel symptoms, and again this is where professionals can offer advice and support.

If you stick to oat consumption longer-term, another review of the literature from researchers at Nevill Hall Hospital, Abergavenny, Wales suggests, given “the long-term effects of a diet containing oats remain unknown”, that coeliac patients should receive “regular follow-up, including small bowel biopsy at a specialist clinic for life” – and that is perhaps the best piece of advice of all.

A selection of brands using or offering GF oats
Big Oz
Bob’s Red Mill
Hale & Hearty
Rude Health

Further reading

Coeliac Disease: What you need to know by Alex Gazzola, is available on Amazon


First published August 2013



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