The food industry has a generally glum outlook for sales in the coming year. But there is a bright spot: the portion of Americans buying gluten-free food has more than doubled in the past three years. Why?

John and Jane Doe, residents of 123 Main Street, Anytown, USA, are just your perfectly average American consumers: board-certified gastroenterologists, who will only purchase "Gluten-Free" food items, because they have scientifically confirmed their own celiac sensitivity with extensive medical testing.