Image: Chefs' Warehouse.Providing specialty food services has become a key part of the restaurant and grocery business, and distributor Chefs' Warehouse (NASDAQ: CHEF) has made it its mission to deliver the goods to hungry customers. Yet the challenge with the food business is always keeping profit margins high, and coming into Tuesday's first-quarter financial report, Chefs' Warehouse investors were concerned that although sales would likely rise at a healthy pace, the bottom line might face some challenges.