fter advising dieters for years to satisfy their hunger with liberal amounts of steak, eggs and other saturated fats, the promoters of the Atkins diet now say that people on their plan should limit the amount of red meat and saturated fat they eat.

Responding to years of criticism from scientists that the Atkins version of a low-carbohydrate, high-fat regimen might lead to heart disease and other health problems, the director of research and education for Atkins Nutritionals, Colette Heimowitz, is telling health professionals in seminars around the country that only 20 percent of a dieter's calories should come from saturated fat. Atkins Nutritionals was set up by Dr. Robert C. Atkins to sell Atkins products and promote the diet.

An Atkins spokesman said Ms. Heimowitz has been giving these seminars for five years, but that they do not represent a departure from the original premise of the diet.

Atkins representatives say that Dr. Atkins, who died last year, always maintained that people should eat other food besides red meat, but had difficulty getting that message out. There has been a revision in expressing how the diet should be followed, not in the diet itself, they say.

But in their consumer publications, Atkins officials have never set limits on saturated fat, and Atkins is widely known as the diet that lets you eat all the meat you want.

Dr. Atkins did more than anyone else to popularize the idea that dieters could eat fat and lose weight. As millions followed his advice, sales of red meat soared and steakhouses grew in popularity. His book "Dr. Atkins' New Diet Revolution" has sold 15 million copies. Atkins Nutritionals reported $100 million in revenues for 2002.

The change comes as Atkins faces competition from other popular low-carbohydrate diets that call for less saturated fat. A book on one such plan, the South Beach Diet, came out in April 2003 and has sold more than five million copies. Atkins representatives made the revision, Ms. Heimowitz said, because "we want physicians to feel comfortable with this diet, and we want people who are going to their physicians with this diet to feel comfortable."

The Atkins regimen remains a high-fat diet. But Atkins officials are specifying the amount that should be saturated — the kind that comes from meat, cheese and butter — and the amount that should be unsaturated — the kind that comes from most vegetable oils and fish. The revision places more emphasis on fish and chicken.

Paul D. Wolff, chief executive of Atkins Nutritionals, said the company is trying to get its message out clearly. "The way the book was promoted was, here's the program that is counterintuitive," he said. " `You can eat a lot of bacon and steak.' It was the marketing of the book. The media saw it as a sexy story."

"Perhaps what was communicated in the past was unclear," he said. "We would agree with that."

So why not tell people straight out that you can't eat all the steak and eggs you want, Mr. Wolff was asked.

"Interesting question," he said as he hung up to catch a plane.

The clarification came as a surprise to Atkins dieters who were interviewed. "A lot of people will be totally shocked," said Ellen Bair, a graphic designer in Brooklyn. The message she said she had taken away from reading Atkins books and Web sites was: "The fat in the diet is very good for you; it doesn't make any difference what kind of fat it is. There are no limits of any kind in the meat department, like steak and eggs for breakfast, a burger for lunch and beef stir-fry for dinner."

Ms. Bair, who said she has lost 48 pounds on the Atkins diet since July 1, said, "Is it possible that now they are revising their thinking?"

Beef, pork, lamb and butter were on the list of "foods you may eat liberally" in "The New Diet Revolution," first published in 1992; its update is No. 1 on the New York Times advice, how-to and miscellaneous paperback best-seller list.

"Atkins for Life," Dr. Atkins's newest book, published a few months before his death, says: "You should always eat a balance of different types of natural fat." The precise proportion of saturated and unsaturated fat was unspecified, Ms. Heimowitz said, because "trying to tell consumers to do math is futile."

Russ Klein, a marketing executive, who has been on Atkins since Dec. 21, interpreted the phrase "foods you may eat liberally" to mean "eat until you are full." And, he added, "I think it's probably true you can eat all the red meat you want."

Ms. Heimowitz said people read the phrase "eat liberally" as a license to gorge on red meat. "Not making a distinction between one kind of protein and another, that was a mistake," Ms. Heimowitz, "and that is why we had to write another book, to get the story straight."

But, she added, "Even in the old book it says `eat until you are satisfied but not stuffed.' "

Total fat in the revised Atkins diet remains much higher than other diets recommend: 60 percent of the calories are still derived from fat, twice the level recommended by the Agriculture Department. Of that, one-third can be saturated fat — also twice the level recommended by the department. The rest should be poly- and mono-unsaturated fats.

That means that a person who eats 1,500 calories a day could eat a 17-ounce strip steak every day, according to Mindy Hermann, a registered dietitian. After the diet's first phase, the amount of fat allowed drops to 55 percent, but the percentage of saturated fat stays the same.

Dr. Atkins said that carbohydrates caused obesity and eating fat helped regulate levels of insulin, which helps produce body fat. Ms. Heimowitz said, "Saturated fat isn't as much of an issue when carbohydrates are controlled; it's only dangerous in excess when carbs are high."

But Dr. Frank M. Sacks, a professor of cardiovascular disease prevention at the Harvard School of Public Health, scoffed at those scientific claims. "What they are saying is ridiculous," he said. The revision, he added, " has nothing to do with science; it has to do with public relations and politics."

The medical establishment largely disputes Dr. Atkins's reasoning and says that high levels of saturated fats are dangerous.

Dr. George L. Blackburn, associate director in the division of nutrition at Harvard Medical School, said the diet's new version is "definitely healthier," but that "all of the studies we have on Atkins are based on the Atkins of the 1970's: eat all you can as long as you keep carbs out."