"So you can't eat all the cheese you want?"

"No, you can't. And you can't eat all the protein you want. And it's not only about bacon and sausage," said Colette Heimowitz, smiling a tight smile through the tedium of my misconceptions, which are apparently not rare.

Heimowitz is politely insistent that her diet—the lead nutritionist at Atkins Nutritionals describes herself as the “keeper of the diet” since the fatal head injury of its namesake Robert Atkins in 2003—was never only about bacon and sausage.

But the original low-carb diet certainly did endear itself to followers by allowing them to partake of processed breakfast meats—any meats, for that matter, as well as cheese, butter, and eggs (“truly luxurious foods without limit,” as Atkins himself did originally put it)—during the era when many doctors believed that saturated fat and cholesterol were the categorical enemies of good health.

The New York physician's original diet has undergone minor modifications over the years, including limits on protein intake and a mandatory vegetable minimum, even if many consumers still think of Atkins as the eat-all-the-meat-you-like diet. This week, though, the company announced its most fundamental redesign. In a move that Heimowitz calls “an evolution based on science” that she believes will unsettle Atkins originalists, the diet plan officially doubled its initial allowable carbohydrate intake.

"If you were a politician," I said, "at this point you’d be accused of flip-flopping."

"Right," she said, laughing politely. "Exactly."

Changing course is a not-insignificant gesture in the business of diet sales, where entrenched ideologies are the norm. And where few messages have been as divisive as Atkins’s. In the wake of the 73-year-old doctor’s death, for example, when the New York medical examiner's office inappropriately leaked medical reports that revealed he weighed 258 pounds, which his family attributed to 60 pounds of water weight due to a viral infection of his heart—not a diet-related issue—detractors jumped to claim otherwise.

“I'm concerned about the Atkins machine trying to play the card that Atkins was healthy and thin into old age,” Neal Barnard, president of the pro-vegetarian advocacy organization Physicians Committee for Responsible Medicine, told The New York Times in 2004. Another physician and member of the organization, John McDougall, claimed to have known Atkins and described him as “grossly overweight. I thought he was 40 to 60 pounds overweight when I saw him, and I'm being kind.”

Nearly half of Americans worry about their weight “all the time” or “some of the time,” according to a Gallup poll conducted last year. That implies a psychological hazard where the health effects of anxiety about weight may be on par with those of excess weight itself—or a misunderstanding of the meaning of “all of the time.” At least part of that is due to uncertainty about nutrition science, perpetuated by profiteering and ego. Recent studies have pointed to superiority of low-carb diets over low-fat diets in matters of weight loss and heart-disease prevention (though neither approach is without its shortcomings), a case well made by journalist Nina Teicholz in her 2014 exoneration of saturated fat, The Big Fat Surprise, which is the result of an exhaustive 10-year scientific and historical review.

Still, according to another Gallup poll last July, only one-quarter of Americans are trying to avoid eating carbs. Twice as many are trying to avoid eating fat.

“The general public is still thinking about low fat and low calories. Low fat, low calories. Low fat, low calories,” Heimowitz said, reiterating the mantra. “It's failed the American population.”

Focusing on calories probably has failed the American population, but so has the fat-carbohydrate duality. The low-carb movement, like the low-fat movement before it, drew people into a macronutrient-centered approach that lumped all carbs together and all fats together, pitting them against each other in an oversimplified tug of war. The Atkins amendment this week is a partial step away from diet extremism, from the proprietors of what was once one of the most influential extreme diets.

That anyone today is consciously, drastically limiting carbohydrate intake is largely attributable to Robert Atkins, whose career arced from counterculture to $400-million bequeathment. Long before this century’s Paleo dieting, breadless sandwiches, and burrito bowls he would come to inspire, Atkins was telling patients in his Manhattan office to focus on eliminating carbs. No other diet had made such generous allowances for fatty meats as Atkins since the declaration of dietary fat as the enemy of health in the 1950s by influential, square-jawed biochemist Ancel Keys. By 1955 Keys had become so powerful that his low-fat attestations brought a prescription for a one-egg-per-week diet to the door of heart-attack-stricken President Dwight Eisenhower.

Lauren Giordano/The Atlantic

Eisenhower would go on to endure at least one subsequent heart attack, and his cholesterol levels continued to rise, before he ultimately died of cardiac disease. But Americans still took to Keys's low-fat diet as salvation for decades. The American Heart Association endorsed the low-fat diet in 1961, and the original USDA food pyramid spread a swath of grains across its foundation, advocating six to 11 servings of bread, cereal, and pasta. Oils and fats (of all kinds) were sequestered at the very tip of the pyramid. As recently as 1999, Teicholz notes, the American Heart Association advised people to avoid fatty foods in favor of "gum drops" and "hard candies made primarily with sugar."

It was during the reign of the low-fat movement that Heimowitz worked alongside Atkins at his Manhattan practice, where she swore by his then-avant-garde technique of near-complete elimination of carbohydrates from his patients’ diets (followed by slow, very modest reintroduction). Particularly for people with extreme obesity and diabetes, who accounted for a substantial contingent of Atkins’ patient population, the improvements seemed clear. In recent years, though, as research on low-carb diets has amassed, Heimowitz says it became evident to her and the other inheritors of the Atkins mantle that most people need not avoid all carbohydrates so strictly as the doctor once advocated.

Atkins first proposed his low-carb diet in the 1972 book Diet Revolution, for which the American Medical Association called him a fraud and he was chastised before a congressional committee.

But the Atkins Diet would go on to win the minds and bodies of nearly one in 10 Americans by 2003. The plan involved four phases beginning with the notorious induction, in which a person is allowed almost no carbohydrates for a matter of weeks (except for a modicum via vegetables and nuts, not to exceed 20 grams, and not including fiber and sugar alcohols). That was followed by incremental introduction of very small amounts of berries, yogurt, legumes, and whole grains. The idea behind near-total carbohydrate avoidance is that when no dietary sugars are around to use as fuel, the body switches to mobilizing stored fat as an energy source. What Heimowitz and company now believe, though, is that state can be achieved even while eating a modest amount of fruits, legumes, yogurt, and whole grains.

“A young athlete could probably do 100 grams [of carbohydrates],” Heimowitz said, “but we're talking to the masses, the general public—how many carbs can they eat and still maintain the principles of Atkins?” Her team settled on 40 grams to start, with steady increases in that number into the 100s as long as a person’s body weight remains stable, all the while hewing to the aforementioned Atkins principles, which she emphasized several times: a focus on optimal protein, healthy fats like avocado and olive oil, and high-fiber carbohydrates within a sustainable method of eating that people can follow long-term.

Those principles are indeed far from anything that would raise the ire of official medical associations or congressional committees today. Heimowitz argues that they long have been, but that mainstream perceptions of the Atkins diet have largely been shaped by people who took up the induction stage and refused to move on.

The “Atkins 40” program launched on Monday.

"January is weight-loss season," Leslie Norden, the publicist who was sitting to Heimowitz’s left as we spoke, chimed in to remind me. Really, the onslaught of press releases and stacks of diet books I've been sent for review preclude me from forgetting. The Atkins 40 plan is available in its entirety for free on the company’s site. Its revenue comes from sales of a line of Atkins-brand foods that are compliant with the diet: frozen foods, bars, shakes, and the like.

"When I was with Dr. Atkins' private practice, his patients were complaining that they were tired of eggs in the morning,” Heimowitz recalled.

“I can’t imagine,” I said, eggs being central to my life.

“Well, I guess after a few years, some people get tired,” she said. So they came up with a low-carb hazelnut bar in the early 1990s, and they couldn't produce it fast enough. That's when Atkins Nutritionals came into existence. Later this year they are introducing a new line of traditional foods made with low-carb ingredients, such pizza made with roasted peppers instead of tomato sauce. There will also be trail mix, and low-carb chocolate and candies—that use a combination of glycerin, polydextrose (a fiber that has a sweet taste), and sugar alcohols—and other products to be released in the fourth quarter of this business year.

Lauren Giordano/The Atlantic

"I think it's the first time that a major nutritional company has put out a diet for free," Norden chimed in again. Indeed it is rare; even Weight Watchers involves some proprietary information that is only available to subscribers. Though Heimowitz is also selling a book, The New Atkins Made Easy: A faster, simpler way to shed weight and feel great. She also authored 2008’s The All-New Atkins Advantage, and 2011’s The New Atkins for a New You Cookbook, both pegged to more minor updates to the Atkins plan—subsequent to filing for bankruptcy amid a plunge in Atkins Nutritionals revenue from $700 million in 2004 to $200 million in 2006.

Atkins 40 includes a mandatory level of vegetable intake, and then allows for 25 grams of carbohydrate "to play with."

So, caring nothing for gum drops, I asked about Sour Patch Kids.

"No," she said, "That's an interesting question." (Is it?) The Atkins program has an "acceptable food list” that includes whole grains, fruits, nuts, and legumes, but not candy. Though the focus is still on protein and fat, it does now recommend a balance of "healthy fats" with "a little saturated fat from animal protein."

The increased carbohydrate allowance is also ostensibly to help people to “learn what carbohydrates are most expensive.” For example, she says, “A white potato has a lot of carbohydrate; you could get 40 grams on one potato. But I could have two cups of berries and two ounces of nuts if I choose those carbohydrates instead.” And in that way, the plan is meant to be sustainable. "If people want a slice of toast with their eggs in the morning," she said, in a tone with which one might allot a pair of socks as a Christmas present, "they can have it."

The first person to try the new higher-carb iteration of the Atkins Diet was long-time “celebrity spokesperson” Sharon Osbourne. Though she reportedly lost 25 pounds on the original Atkins 20, Heimowitz said she would gain five pounds back “every time she went on the road with Ozzy.”

“I would always have to put her back on induction,” Heimowitz said, “I could never get her through the phases because she would either be on or off the diet. But now she has been maintaining her weight loss for close to two years.”

Before she worked for Atkins, Norden confessed to me, she was a “crazy CrossFitter”—a part of the workout-lifestyle franchise that has become entwined with Paleo dieting. The popularity of the similarly low-carb Paleo has only been positive for the Atkins team, they say, cultivating in people what Heimowitz calls a “carbohydrate conscience,” an awareness that too much is bad. But she argues that the Paleo diet is too restrictive in terms of choice, limiting carbohydrates by quality rather than quantity.

“You could eat all healthy carbs and still get fat," Heimowitz said. (Teicholz makes the same point, that even unprocessed carbs like whole-grain oatmeal and pastas as a primary source of calories can ultimately be less healthy than one of eggs, bacon, and fish.) "If you're eating potatoes and rice and beans, beyond your carbohydrate tolerance, you're going to get fat."

"Well, you can't have any of that on Paleo," Norden added.

"Paleolithic people had no beans?" I asked.

"Right,” she said, “no legumes.”

That I had to verify, and it's true that the Paleo diet officially does not include beans, peas, lentils, peanuts, and other legumes, which were not part of the human diet at the time. But on what grounds? Loren Cordain, professor emeritus at Colorado State University and ringleader of the Paleolithic diet, explains in a recent 4,900-word response to "a question that comes up time and again, 'Why can’t I eat beans?'" In what devolves into an assiduously footnoted screed, Cordain argues that kidney beans are “toxic poisons” and “legumes are inferior foods that should not be part of any contemporary Paleo diet.” The heart of his reasoning is that legumes have relatively low protein, zinc, and iron contents compared to animal meats. (Maybe someone deficient in those nutrients could do well to choose meat over beans, but most people get enough either way. That's not to mention the environmental case against eating meat 24-7.)

Cordain's case for toxicity involves specious claims about certain legume components in animal and cellular models, and in people with hereditary enzymatic deficiencies. The whole thing reads not as an honest inquiry into the prudence of eating beans, but a compilation of any possible shred of conceivable evidence to support his notion that humans are not meant to eat foods that were not part of the human diet in the Paleolithic era.

Only at the very end of the piece does Cordain mention that in the past, whenever he ate beans or legumes, he “experienced digestive upset, gas, and frequently had diarrhea.” So he stopped eating them, his situation improved, and ultimately the most important message is to listen to one’s body.

His seventh book on the Paleo diet comes out in March.