Gluten is a protein found in wheat, which humans have been eating for thousands of years. Now, though, nearly a third of American adults are trying to cut it from their diets.
About one percent have Celiac disease. They say gluten can damage their intestines. Others say gluten has other negative effects on their health, including acne, infertility, IBS, and fatigue.
As the gluten-free approach grows, sales of gluten-free food are growing, too. Sales are expected to top 15 billion dollars by 2016.
Doctors, for their part, don't know why.
"I believe it's a little of both," said Dr. Steven Lamm of NYU Langone Medical Center, when asked if gluten-free is a fad diet or if there are legitimate health concerns associated with it.
Even though gluten has been around for thousands of years, Dr. Lamm says people may be more sensitive to it now because there is more of it.
"Wheat products from thousands of years ago probably have less gluten than they do now."
Now, researchers are trying to determine whether another component in wheat -- a carbohydrate called fodmaps -- may actually be what causes problems.