Gluten is a protein found in wheat, rye and barley. It causes some people serious health problems. But those people don't seem to be the only ones buying the gluten-free beer and brownies suddenly for sale everywhere. Consider:

• Marketers estimate that 15% to 25% of consumers want gluten-free foods — though doctors estimate just 1% have celiac disease, the best-defined and most severe form of gluten intolerance, says Cynthia Kupper, executive director of the non-profit Gluten Intolerance Group of North America (gluten.net).