The nation's appetite for low-carbohydrate foods seems bottomless, judging by the many low-carb products showing up in supermarkets and the new menu items at restaurants and fast-food chains. And when Krispy Kreme Doughnuts Inc. recently announced slowing sales, it put part of the blame on low-carb diets.More in linkYet the mood at a recent Washington conference on the business was bleak. Sales of low-carb products have fallen sharply at independent and health food stores, and some longtime industry insiders say a shakeout has begun.