Not all 'gluten-free' foods sold in eateries are actually free of the potentially harmful protein, people with coeliac disease have been warned.
Treatment of coeliac disease includes a lifelong strictly gluten-free diet; exposure to even tiny amounts of gluten can damage the person's small intestine.
Gluten can be found in grains such as wheat, rye, barley and oats.
But a study published in the Medical Journal of Australia on Monday has detected potentially harmful levels of gluten in foods sold and served as 'gluten free' across Melbourne.
It also revealed a lack of understanding among food staff about the foods that do and don't contain gluten.
Researchers, led by gastroenterologist Dr Jason Tye-Din at the Walter and Eliza Hall Institute of Medical Research and Royal Melbourne Hospital, analysed 158 'gluten-free' dishes from 127 randomly selected food businesses in Melbourne.
They found nine per cent, or 14, contained detectable gluten and were therefore not compliant with the Food Standards Australia New Zealand (FSANZ) definition of gluten-free.
Of these non-compliant dishes, nine contained more than 20 parts per million (ppm) gluten, the upper threshold for safe gluten intake in Europe and the United States.
"One business provided wheat-based foods (> 80 ppm gluten) despite a gluten-free meal being requested, reflecting the lack of understanding reported by many people with coeliac disease," the authors wrote.
An additional survey of food staff found only 10 per cent had 'good' knowledge of FSANZ guidelines.
They were also "particularly ignorant" about spelt, which contains gluten.
The good news was that non-compliance rates had improved since earlier audits in 2014 and 2015, most likely due to greater scrutiny by environmental health officers and education.
"Indeed, four of five venues of one burger chain were non-compliant in 2014, but all were fully-compliant in 2015 and 2016," the authors said.
"The increasing community demand for gluten-free food may also be a driver of increased awareness among food service staff of the importance of avoiding gluten contamination."
The authors, with support of Coeliac Australia, say the study shows education and training are vital for food businesses serving gluten-free food.
"Improving training and knowledge about appropriate gluten-free food practices is probably the single-most important step in ensuring the safe delivery of gluten-free food, particularly for people with coeliac disease, whose health depends upon it," they wrote.