Justin Pedersen pays careful attention to food labels when he goes shopping.

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Four years ago, the 36-year-old Melburnian cut gluten out of his diet for health reasons.

"I trust the label," Mr Pedersen said.

"A lot of products now have the words gluten-free on the box so I don't even have to read the ingredients. A lot of products still don't have that, so you've just got to turn to the ingredients."

But some products labelled gluten-free on the supermarket shelf may not be what they claim to be, a new study has revealed.

About one in 40 products tested by Australian researchers did not meet national food standards that require foods labelled as "gluten-free" to contain no detectable gluten.

Gastroenterologist Jason Tye-Din said the findings, reported today in the Medical Journal of Australia, indicated food manufacturers needed to test their products more frequently.

"Even though the vast majority of the products are very safe, there is a signal here that perhaps there could be an improvement in practices," Dr Tye-Din of the Walter and Eliza Hall Institute said.

Why gluten-free is important

Gluten is a group of proteins found in wheat, barley, rye, and spelt.

Many people with gluten sensitivity like Mr Pedersen feel better after cutting out food and drinks that contain gluten.

But avoiding gluten is critical for people who have been diagnosed with coeliac disease — an autoimmune reaction to gluten that damages the lining of the small intestine and affects a range of organs in the body.

"Coeliac disease can cause multiple effects in the body apart from just a tummy upset — issues like anaemia, infertility, liver disease, some forms of cancer and osteoporosis," Dr Tye-Din said.

"The only treatment is a lifelong and strict gluten-free diet."

"People who require a strict gluten-free diet should be able to trust it conforms to the national standard and that it will be safe for them to eat."

Coeliac disease vs gluten sensitivity Coeliac disease affects around one in 70 Australians

Coeliac disease affects around one in 70 Australians It is an autoimmune condition that destroys the villi (pictured above) that line the small intestine. This affects the ability to absorb nutrients.

It is an autoimmune condition that destroys the villi (pictured above) that line the small intestine. This affects the ability to absorb nutrients. It can cause vomiting, diarrhoea, anaemia, osteoporosis and inflammation of other body organs.

It can cause vomiting, diarrhoea, anaemia, osteoporosis and inflammation of other body organs. Severity of symptoms vary from person to person. Some people can have symptoms after eating a tiny amount while others can eat a loaf of bread and not have symptoms but the gluten still affects their body

Severity of symptoms vary from person to person. Some people can have symptoms after eating a tiny amount while others can eat a loaf of bread and not have symptoms but the gluten still affects their body Correct diagnosis is essential

Correct diagnosis is essential People with coeliac disease test positive to a blood antibody. A diagnosis is confirmed by a tissue biopsy. You must be still consuming gluten for these tests to be accurate

People with coeliac disease test positive to a blood antibody. A diagnosis is confirmed by a tissue biopsy. You must be still consuming gluten for these tests to be accurate You can also be tested for a gene. Between 40 and 50 per cent of the Australian population test positive to this gene. All people with coeliac disease test positive to this gene, but not all people who test positive have coeliac disease

To get snapshot of what was on the shelves, Dr Tye-Din and colleagues identified the 300 most popular gluten-free products such as noodles, crackers, fruit bars, rice snacks and pasta.

They purchased samples of 256 of the products and sent them off to the National Measurement Institute in Melbourne for independent testing.

"Low levels" of gluten were detected in seven of the products, Dr Tye-Din said.

While Australia and New Zealand have strict zero limits for gluten, Europe, the US and UK permit up to 20 parts per million (ppm).

Six out of the seven contaminated products had between just under five and 24 ppm (less than half a milligram per standard serve). But one pasta item had 49 ppm (just over 3 mg per serve).

"This could be harmful if people are consuming these food items on a regular basis," Dr Tye-Din said, stressing that regular meant eating pasta several times a day for at least three months.

"Unless you're eating truckloads you're very unlikely to run into issues."

The team re-checked the levels and purchased more samples of six of the affected products (one product, rice snacks, had been recalled by the manufacturer).

They also found traces of gluten in the retested samples.

"It suggests this was not an isolated event. Something didn't just fall into the conveyor belt, but it suggests maybe a more systemic process going on, for example something to do with the sourcing of food items," Dr Tye-Din said.

"Interestingly, many of these companies were dedicated gluten-free factories so it's hard to imagine that gluten would be obviously coming in," he added.

Manufacturers informed of results

Dr Tye-Din said the results had been sent on to the manufacturers, the names of which and the affected products have not been released.

"If companies adopted a more regular screening approach of each batch — which we know many companies do — they're likely to pick up these issues," he said.

"We only tested 256 items, there's thousands of different things out there.

"What if some of these others have more?"

Dr Tye-Din said his group is working with the manufacturers and continuing to monitor the affected products.

Coeliac Australia, which part funded the study, welcomed the finding that a majority of gluten-free products met the Australian standards.

"It is important that people have trust in the gluten-free items they purchase as it does relate to their health," a spokesperson said in a statement to the ABC.

"However, as almost 3 per cent of samples did have some detectable gluten, even if it was at very low levels, we feel this is an important issue."

"The research signals a minority of manufacturers do need to review their processes to ensure products truly are gluten-free and meet Australian standards," they said.

Dr Tye-Din's study follows up earlier research focusing on gluten-free foods served in Melbourne restaurants.

That study, published earlier this year, found gluten in 9 per cent of gluten-free meals at much higher levels than those found in manufactured foods.

"In the scheme of things people are pretty safe eating gluten-free manufactured products. The risk is much more real if they're eating out at restaurants and food services," he said.

Mr Pedersen said going out was a lot trickier.

"You can't read labels or ingredients lists. You rely a lot on the word of people serving you."