Powerhouses like Kroger Co., 7-Eleven Inc. and Wal-Mart Stores Inc. are throwing their weight behind low-carb products, hoping to expand their bottom lines while shrinking those of their shoppers.

And restaurants like the Vineyards Cafe in Farmington Hills, Mich., are drawing crowds with low-carb sandwiches wrapped in lettuce instead of bread."It's so filling it's unbelievable," said Vineyards owner Ron Asmar, a former yo-yo dieter who has been on a no-carb regimen for five years.

For retailers, low-carb has made the transition from a fad or trend. It's now a lifestyle, and consumer surveys show it is likely to influence shopper behavior for years.

Dieting is now an American way of life. An estimated 65 percent of U.S. adults are overweight or obese, according to research by the Atlanta-based Centers for Disease Control and Prevention.

Marketdata Enterprises Inc., a Tampa, Fla.-based research firm, estimates that the total U.S. weight-loss market was worth $39.8 billion in 2002, up 6.6 percent from 2001. Marketdata projects that it will hit $48.8 billion by 2006.

"Low-carb is here to stay," said Phil Lempert, a Santa Monica, Calif.-based expert on food marketing whose own diet is being tracked on his Web site, SupermarketGuru.com.

Consider this: Sales at New York-based Atkins Nutritionals Inc., which sells Atkins products and information, are expected to double this year from $100 million in 2002.

The privately held company estimates that 25 million people are on the Atkins diet, named after the late Dr. Robert C. Atkins, whose first low-carb missive was published 30 years ago.

In his 1972 book, "Dr. Atkins' Diet Revolution," the controversial doctor recommended a diet in which up to two-thirds of calories come from fat, more than double the traditional recommendation.

Since then, the diet's popularity has grown. Its real sizzle came in the past few months following studies that show these diets can be safe and effective.

Retailers noticed the shift in consumer habits and began to respond. Atkins-branded food and supplements are available in more than 30,000 stores nationwide.

A California franchise group is even trying to launch a chain of low-carb superstores called Castus, named after a Latin word meaning "clean and pure."

"Everybody's interested these days in losing weight," said Danette Thompson, a spokeswoman for Wal-Mart Stores Inc., which sells Atkins bars, drinks and supplements at its discount stores and supercenters.

As a result, companies such as Heinz, Anheuser-Busch and Breyers, which once made their bread and butter from carbohydrate-heavy foods, are among those stocking the shelves with low-carb items.

Heinz's new One Carb Ketchup "is designed for consumers who wish to moderate their carbohydrate intake without having to compromise on taste," the company said.

The low-carb market is so new that relatively few statistics exist to show the growing popularity of these diets, said Marketdata Research Director John LaRosa.

But the anecdotal evidence is impressive. For example, 120,000 people became paying subscribers at eDiets.com in the first four months that the Web site began offering the Atkins plan, LaRosa said.