Though some of these fast-food places now offer a few low-fat items, the big sales and profits are in hamburgers, French fries, milkshakes, fried chicken, and greasy pizza -- the very things that the ');">U.S. surgeon general says are fueling America's obesity epidemic. Which makes you wonder, as you drive past one burger place after another, why someone hasn't made a billion dollars by opening fast-serve restaurants that offer nourishing, expertly prepared, low-fat meals. Why not, indeed, when we can find tasty baked chicken, broiled fish, veggies and the like at sit-down restaurants and upscale grocery stores? According to Bryan Elliott, a food-industry analyst at Raymond James and Associates, some entrepreneurs have tried this idea -- and gone bankrupt. That's because the ingredients and technology to mass-produce nutritious food are much more costly, and it's hard to find low-paid line cooks who can quickly prepare low-fat, but interesting, dishes. Bryan Elliott says chains serving healthful fast food WILL evolve, once costs come down or Americans get used to the idea of ordering, and paying a bit more for, a quick lentilburger and salad instead of cheeseburger and fries on the road.