If you have a severe intolerance to gluten, a chemical in your diet may (at least partly) be to blame.
We are not talking about gluten allergies or sensitivities here, but celiac disease – a lifelong autoimmune disorder affecting roughly one in 100 people where the ingestion of gluten provokes an immune system attack on the gut. Experts aren't sure of the exact cause. However, a paper recently published in Frontiers in Pediatrics has linked a common food additive to the disease: Microbial transglutaminase.
Transglutaminase is a bacterial enzyme often added to food during manufacturing. You can find it in a lot of processed food, from dairy and meat to baked goods.
"Microbial transglutaminase can glue together proteins, so it's used to improve food texture, palatability and shelf-life," co-author Aaron Lerner said in a statement.
"This enzyme functions like the transglutaminase produced by our body, which is known to be the target of autoimmunity in celiac disease."
The problem is that transglutaminase doesn't just help extend shelf-life, improve texture, and even lower calories, it actually changes the structure of gluten protein fragments (or peptides), making them harder for the body to break down than they are already.
"These unusual peptides are particularly likely to resist further breakdown, and to be recognized as 'foreign' by HLA-DQ immune receptors inside the gut wall – but only in those carrying the HLA-DQ variants associated with celiac disease," Lerner added.
Around 30 percent of people carry one of two HLA-DQ variants that put them at greater risk of developing the condition. These genes are so crucial to its development that virtually all sufferers have one of the variants but not all carriers go on to develop the disorder. And this is where biologists suspect environmental triggers play a role.
To make matters worse, transglutaminase does not simply make the peptides harder to break down. It may even modify the proteins that hold together the intestinal barrier, meaning more gluten-derived proteins and microbial transglutaminase molecules are able to seep through the barrier and interact with the body's immune cells.
The body produces its own transglutaminase so you might not expect a little extra to do much harm. But Lerner says it's to do with scale and structure.
"Our own transglutaminase has a different structure to the microbial sort, which allows its activity to be tightly controlled," Lerner said.
"While the relatively indiscriminate microbial transglutaminase is produced by some of our normal gut fauna, the amount of the enzyme could be significantly increased when this microbial population is altered by factors like infection, antibiotics or stress – or, indeed, through consumption of industrially processed foods."
As the researchers say themselves, the jury is still out on transglutaminase and its role in celiac disease. But until further testing confirms whether or not the enzyme triggers the immune system to attack the gut, Lerner and his colleagues advise food manufacturers to label any product that contains microbial transglutaminase, giving celiacs the option to avoid it – as is already the case in Switzerland.