(FORTUNE Small Business) – Even with all the negative buzz that surrounds supersizing, consumers still have undersized appetites for healthier fare. Just ask the latest crop of entrepreneurs who have tried to serve healthy fast food. Recent casualties include Chicago's HeartWise Express and national chains Briazz, based in Seattle, and Fresh Choice of California. The two chains filed for Chapter 11 earlier this year. The problem, according to market researcher Bob Sandelman, whose Sandelman & Associates, based in Villa Park, Calif., tracks trends for the food-service industry, is that consumers say one thing and do another. "Customers will tell you they're concerned" about their health, he says, "but most really just go for convenience and taste." Nonetheless, George Naddaff, the entrepreneur who discovered Boston Chicken, has big plans for his healthy chain, KnowFat Franchise Co. (pictured at left). "It has to taste good, and that's why these other places didn't survive," he insists. Meanwhile, McDonald's sales were up 13%, to $9.1 billion, in the first half of this year. —L.G.