The 500-Calorie Smackdown Two restaurants. Two menus. Two plans for major national expansion during roughly the same time frame. Let the food fight begin.

You would think the American fascination with health and fitness has hit critical mass: Freezer cases are full of low-cal meals in grocery stores and farmers markets are booming. Mini gyms and yoga studios have filled in almost every vacant street corner. Fitness themes have even wiggled their way into the domains of their archenemies: video games and network television. But there is one industry--perhaps the one with the best chance of helping us fit into our skinny jeans--that has remained stubbornly out of step when it comes to our obsession with shaping up: restaurants.

A generation ago, dining out was an indulgence--but today, the average American grabs something off the menu four to five times a week. More than a few of us dine out almost nightly, and the numbers seem to be trending upward. Michael Pollan, the voice of the "real food" revolution, has said cooking at home will be as odd to our grandchildren as slaughtering a chicken is to us. The problem is, while eating out has lost its Friday-night glamour and corner booths have replaced the dining room, restaurants are still stuck on their legacy of indulgence, serving enormous portions and spiking them with more and more fat, salt and sugar.