One of the defining food trends of our time is the speed with which rare allergies and diseases magically expand to include vast swaths of the population. The latest example is celiac disease, a rare autoimmune condition triggered by gluten, a protein composite found in most kinds of bread. Since bread is fattening, and dispensable, and because so many of us are hypochondriacs, gluten-free foods keep surging to ever higher levels of popularity, rivaling artisanal as a marketing shibboleth.