Sunday, 5 October 2014

Toxicity of Oats in Individuals with Coeliac Disease

Scientific Literature
 
A number of studies have reviewed the toxicity of oats in individuals with Coeliac disease.  In a recent review of studies published since 1995, Thompson (2003) concluded that the body of research on oats supports the conclusion that most adults with Coeliac disease can consume moderate amounts of uncontaminated oats without causing damage to the intestinal mucosa.  However, it is not known whether this is due to oats lacking in harmful amino acid sequences or due to those sequences occurring in small enough quantities so as to not cause a problem.

Thompson (2003) also noted some concerns with the methodologic limitations of some of these studies.  One issue that was noted relates to the differences in the protein composition of oats versus that of wheat, rye and barley.  Wheat, rye and barley prolamins account for 30% to 50% of total protein, whereas oat prolamins account for only 10% to 15% of total protein.   Therefore, it has been suggested that a far greater quantity of oats would have to be consumed to cause the same adverse effects as wheat, rye or barley.

In one of the most recent of such studies, Picarelli (2001) aimed to define the role of oats in Coeliac disease to determine whether oats can be safely included in a gluten free diet. The study design involved an in vitro model to test whether oats induced antiendomysial antibodies production in supernatant fluid from cultured duodenal mucosa specimens collected from 13 treated Coeliac disease patients. Antiendomysial antibodies are produced by intestinal mucosa and are highly sensitive and specific for Coeliac disease. The biopsy specimens were cultured with and without peptic-tryptic (PT) digest of gliadin and avenin (from oats) and in medium alone. Samples from 5 of the 13 patients were cultured with the C fraction of PT-avenin. Antiendomysial antibodies were detected in specimens from all 13 patients after the challenge with gliadin but not after culture with medium alone. By contrast, no antiendomysial antibodies were detected in any of the specimens cultured with PT-avenin and its C fraction. Given this, it was concluded that oats can be safely included in the gluten free diet of people with Coeliac disease.

In agreement, Janatuinen et al. (2002) aimed to assess the safety of long term ingestion of oats in the diet of Coeliac patients. In an initial study, the effects of a gluten free diet and a gluten free diet including oats were compared in a randomised trial involving 92 adult patients with Coeliac disease, with 45 in the oats group and 47 in the normal group. After 6-12 months, patients in the oats group were able to eat oats freely with an otherwise gluten free diet. After 5 years, 35 patients in the original oats group (23 still on an oats diet) and 28 in the control group on a conventional gluten free diet were examined (Janatuinen, 2002). Clinical and nutritional assessments were undertaken, duodenal biopsies for conventional histopathology and histomorphometry were examined and a number of antibodies were measured. The study found that there was no significant difference between the normal group and those people consuming oats with respect to duodenal villous architecture, inflammatory cell infiltration of the duodenal mucosa, or antibody titres after five years of follow up. In both groups histological and histomorphometric indexes improved over time. It was concluded that both adults and children with Coeliac disease can use oats as part of an otherwise gluten free diet and that even long term use of moderate amounts of oats included in a gluten free diet in adult patients with Coeliac disease is safe. 

Janatuinen (2002) suggests that the reason why individuals with Coeliac disease can tolerate oats is based on structural differences of proteins among oats, wheat, barley and rye. It is recognised that the injurious agent in wheat is the gliadins and it is possible that the absence of certain amino acid sequences from oat avenin that are found in wheat gliadin, make oats tolerable to people with Coeliac disease.

In addition, Janatuinen et al. (2002) recognises that recent guidelines from the Finnish and the UK Coeliac Societies conclude that moderate amounts of oats can be consumed by most individuals with Coeliac disease without risk. The guidelines also suggest that removal of oats from the list of forbidden cereals in the diet for people with Coeliac disease could increase compliance with a gluten free diet by giving more choices and reducing the cost of gluten free foods.

 
Views of the External Advisory Group

Consultations with the Dietary Management EAG on the issue of the toxicity of oats in individuals with Coeliac disease revealed that opinion was divided.  Although it was acknowledged that a number of studies have been published indicating that oats can be tolerated by many people with Coeliac disease, there was no overall agreement amongst members that this information is conclusive.  Representative health professionals in New Zealand were of the view that the majority of Coeliac patients can tolerate some oats in the diet. However, representative Australian health professionals indicated that not all Coeliacs can tolerate oats, therefore the prohibition on oats in gluten free claims should be retained. 

A further issue to be considered is the potential contamination of oats with protein from other sources such as wheat or barley. It has been suggested by the Analytical Methodology EAG, that contamination is an issue, rarely with wheat, but more likely with barley, with an estimated contamination level of 0.04 - 0.05%. Given this and assuming that there is 10% protein in the contaminant, the Analytical Methodology EAG, suggested that the gluten level in oats would be around 0.004-0.005%.

Submissions

Views were mixed amongst submitters to the P264 IAR in relation to the toxicity of oats, particularly in relation to whether there should be a specific prohibition of gluten free and low gluten claims on foods containing oats. Many submitters referred to recent studies indicating that the majority of people with Coeliac disease can tolerate oats, and that therefore there should not be a specific prohibition of gluten claims on foods containing oats in the Code. Others however, felt that while evidence is not absolutely conclusive, caution should be applied within the regulatory setting. The rationale provided for this approach included the following points:
  • although studies found that the majority of people could tolerate oats, it was noted that the studies have limitations and that more work is required to resolve the issue;

  •  it was suggested that approximately 15% of Coeliac sufferers who ate oats reacted symptomatically and if the prevalence of Coeliac disease in Australia and New Zealand is 1:250-300, this represents a significant number of people who may react symptomatically to the presence of oats in gluten free foods; and

  • the potential contamination of oats with barley or wheat presents a problem for people with Coeliac disease. Although studies have shown a certain degree of tolerance to oats amongst people with Coeliac disease, in many cases uncontaminated oats were used which do not necessarily represent the food supply where uncontaminated oats are less freely available.

In relation to the issue of contamination, the question was raised in the IAR as to whether the risk of contamination with protein from other sources is an appropriate basis for excluding a significant cereal source from carrying a gluten claim? Further to this, one submitter made the point that there are no other provisions in the Code that regulate for cross-contamination during processing.

Excerpt from www.foodstandards.gov.au/

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