The health benefits of a gluten-free diet might also be a kind of self-fulfilling prophecy. It's well-known that our digestive system adapts its secretions (rather quickly) to whatever we're eating. ... Now imagine that you've cut out gluten from your diet completely—that means no bread, no cereal, no wheat whatsoever. Chances are you'll have reduced your total intake of carbs, and thus the amount of α-amylase in your gut. In other words, the mere fact of being on a gluten-free diet could make you more sensitive to grains and cereals—which would only reinforce your conviction that you're gluten-intolerant. Slip up for even one meal, and you'll pay the price with indigestion.
--Daniel Engber, Slate, on why gluten intolerance might be on the rise