Concerning new research suggests over half of popular probiotics contain traces of gluten, meaning they could have the opposite effect on certain people hoping to achieve digestive health.

Probiotics are usually taken to promote gut health, but an analysis of 22 top-selling probiotics revealed 55 percent contained detectable gluten, the Celiac Disease Center at Columbia University reported.

"Many patients with celiac disease take dietary supplements, and probiotics are particularly popular," said Samantha Nazareth, a gastroenterologist at CUMC and the first author of the study. "We have previously reported that celiac patients who use dietary supplements have more symptoms than non-users, so we decided to test the probiotics for gluten contamination," said Samantha Nazareth, a gastroenterologist at CUMC and the first author of the study.

Gluten is a protein found in grains, such as wheat and barley, and patients suffering from celiac disease must eliminate them from their diet in order to find relief from bowel symptoms, and even to decrease their risk of cancer.

A team of researchers used liquid chromatography-mass spectrometry to detect gluten content in a variety of popular probiotics. Most of the samples that tested positive for gluten contained less than 20 parts per million, which is considered "gluten free" by the Food and Drug Administration (FDA), but four samples exceeded that amount.

"We have been following reports in the scientific literature and news media on inaccurate labeling of nutritional supplements, and it appears that labels claiming a product is gluten-free are not to be trusted, at least when it comes to probiotics," said Peter Green, professor of medicine and director of the Celiac Disease Center, "This is a potential hazard for our patients, and we are concerned."

The study did not determine whether or not these levels of gluten found in the probiotics could trigger symptoms in patients with celiac disease.

"We know that most patients with celiac disease only develop intestinal damage when consuming more than 10 milligrams of gluten daily, and it is unlikely that contaminated probiotics can lead to that amount unless patients are ingesting mega-doses²," said Benjamin Lebwohl, assistant professor of medicine and epidemiology at the Celiac Disease Center and a co-author of the study. "Why is there any gluten in these products? Why should the consumer pay any attention to gluten-free labeling on such products? And given the great consumer interest in probiotics, will regulatory bodies take action to protect the public?"

The study will be presented at Digestive and Disease Week (DDW).