What about the discrepancy in shipments and grocery sales? She said Nielsen doesn't include sales from the likes of Whole Foods, Costco, Trader Joe's and sales in Canada. To fill that consumption-data void, she says, "We use shipments in an attempt to capture the entire market." As for receivables racing ahead of sales, Sacco said it's the result of acquiring and integrating Glutino and Udi's and "offering extended days across the business to align company terms." But is the gluten-free sales trend sustainable? Or like most fads will it flame out? And with so much of its sales tied to gluten-free, will Boulder Brands be vulnerable? "We think it's similar to organic in its day," Sacco said. Apples and Oranges Reality: Organic and gluten free are two distinctly different categories and comparing them really is (given the health-food nature of the discussion) apples and oranges. Still, there's no getting around it. Gluten free's growth has been explosive. But it's unclear, even as it goes mainstream, how much staying power and sustainable growth it really has. Annie's CEO John Foraker acknowledged as much at a recent investment conference when he said that even though gluten-free products have been growing quickly, faster than his overall business, "we also are cognizant that some consumers are in gluten-free maybe for diet reasons and other things which maybe are not as sustainable." Meanwhile, with growth comes competition. The latest entry: Goodbye Gluten from baking giant Grupo Bimbo, whose brands include Arnold, Oroweat, Sara Lee, Thomas and Entenmann's. And if the general public winds up tiring of gluten free, they're all battling for a real market, among diagnosed celiacs in the U.S., which numbers a whopping (wait for it) 3 million people, or about 1% of the population. Disclosure: My daughter is celiac and I've spent a tremendous amount of time with her at Columbia University's Celiac Center, including multiple meetings with the center's nutritionist. I've researched the subject the way any parent (a journalist, no less) would. I've read. I've interviewed. I've become engrossed. To see what my daughter would be going through, I put myself on a temporary gluten-free diet, only to be chastised by the Celiac Center's nutritionist, who told me point blank that if you're not celiac you should not eat a gluten-free diet. Her reasoning is that it tends to be higher in calories and less nutritious.