Diets never die, and to prove it, Atkins is back in the limelight.

“The New Atkins for a New You” hit bookstores in March, bringing with it a $20 million ad campaign. Private-equity firm North Castle Partners of Greenwich, Conn., acquired the waning brand two years ago, and the new C.E.O. of Atkins Nutritionals, Monty Sharma, is determined to see low carb flying high again. He's changed recipes, culled retail products and is even changing the diet's focus.

“No more of the ‘meat all the time,’” says Sharma. “People have to eat vegetables, too. “

Atkins' retail offerings have been reduced from 200 products to 64. The company's nutrition bars, which were previously criticized as bland, are now sweeter, even though they still have only one gram of sugar. That's because the bars are smaller—1.4 oz. compared to 2.1. Sales in 2009 reached $170 million, a 30 percent increase over 2008, says Sharma.

But some believe that Atkins will struggle to reproduce its earlier success, despite the company's multimillion-dollar efforts, as food companies develop their own diet foods and reduce the amount of sugar and carbohydrates in their regular items.

“The low-carb niche would be a hard sell to any big company,” says Rick Shea, marketing consultant and former vice president of marketing at Kraft.