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Call it Paleo Chic. The eating habits of cavemen have never been more popular. But should we be taking menu cues from our ancient ancestors?

The protein-heavy, low-carb principles of the Paleo diet are popping up in restaurants like HG SPLY Co. in Dallas and Hu Kitchen in New York City; exotic new Paleo-inspired products such as grass-fed beef pemmican, a Native American meat paste, are hitting the shelves. And celebrities from Miley Cyrus to Kobe Bryant are reportedly avid followers.

While the Paleo diet has been around for years, it’s just now gaining some mastodon-like momentum. But many nutrition experts are not impressed. On June 3, Scientific American ran a long story that ridiculed the Paleo diet as “half-baked.” The magazine suggested that the caveman the movement was imagining—“a tall, lean, ripped and agile 30-year-old” was an invention. Though cutting down on preservative-packed processed foods was smart, the article noted, the idea that banning “any kind of food unavailable to Stone Age hunter-gatherers,” including dairy products, grains and beans, was nutritional bad-think.

Likewise, U.S. News, in its 2014 rankings of “Best Diets Overall,” announced that the Paleo diet was at the very bottom, tied at No. 31 with the Dukan diet. “Experts took issue with the diet on every measure,” the magazine scolded.

What is the experts’ beef, as it were, with the diet? When it first surfaced in academic circles in the late 1970s, and as popular diet books started emerging in the 1990s, the program was promoted as a lifestyle as well as a weight-loss method, first cousin to Dr. Atkins and the low-carb craze.

The theory behind the diet is simple: our hunter-gatherer forebears, who survived on meat and fish that was not saturated with growth-stimulating antibiotics or hormones, as well as on fresh fruits and vegetables, were on the right track until the Agricultural Revolution introduced toxins into the food chain some 10,000 years ago. So the goal is for citizens of the 21st Century to lean back—way back—and eat the way primitive people did in the Paleolithic Era, circa two million years ago.

But dieticians find its restrictive, even finicky, requirements such as sticking with very lean, pure meats and plants, unrealistic. As Scientific American put it, “The Paleo diet is founded more on privilege than on logic. Hunter-fathers in the Paleolithic hunted and gathered because they had to. Paleo dieters attempt to eat like hunter-gatherers because they want to.” Any diet that restricts certain food groups and emphasizes others isn’t balanced, these experts say, and there isn’t strong science to prove that Paleo-eaters live longer, or are healthier than those who don’t follow the diet.

Marlene Zuk, an evolutionary biologist at the University of Minnesota, has a different gripe. In her new book, “Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live,” she rips apart many of the contemporary notions about our Paleolithic ancestors. “I didn’t write a diet book,” she says, “and I don’t want to tell people how to eat. But I do want people to understand evolution.”

But the Paleo crowd passionately defends its ancestral diet. Kellyann Petrucci, a nutritional clinician who is the author of three popular “Dummies” book about the Paleo lifestyle (“Living Paleo,” “Paleo Cookbook” and “Paleo Workouts), offers herself as Exhibit A of the benefits of primal habits. “I became interested in Paleo because when I hit 40 a few years back, I crashed and burned,” she says. “I was gaining weight like crazy…my skin looked lifeless, my hair started thinning and I had no energy. When I followed the Paleo template, it was clear to me that something was happening on a deep cellular level. Not only did I get myself back, but a healthier, more vibrant version.”

Perhaps the most outspoken defender of Paleodom is Chris Kresser, whose new book “Your Personal Paleo Code” (read excerpt here) provides a detailed road map to the lifestyle. Kresser, who practices integrative and functional medicine in Berkeley, Cal., credits the diet with restoring his own health after years of a painful digestive disease. “Today, I’m blessed with excellent health, a loving family, and a flourishing practice,” he says.

Kresser argues that science in fact supports the Paleo principles: “There is broad consensus among scientists that our Paleolithic ancestors consumed primarily meat, fish, vegetables, fruits, nuts, seeds and starchy tubers.” He rejects the claim that the diet is too labor-intensive for the average person, or that it’s hard to find the ingredients of these ancient diets, citing a plethora of restaurants and new convenience foods such as gluten-/sugar-/soy-free beef jerky, kale chips and grain-free crackers and deserts.

In the past three years, he says he has treated 900 people in his Berkeley, California office. “My practice has been closed to new patients for most of the last two years,” he says, “because there is such a high demand for clinicians who embrace Paleo in their work.” Kresser says that the diet is booming in popularity because “Many people experience a profound transformation in their health after switching to Paleo and they’re excited to share that with others. This has created a powerful, grassroots, word-of-mouth movement of people eager to spread the word.”

That word alone isn’t enough, however. New York City nutritionist Jennifer Andrus sees some nutritionally wise principles in the diet, such as the lean meats and fish, and fruits and vegetables, but says it’s not necessary to go to the extremes of the Paleo crowd. “It eliminates dairy, legumes and some other foods that can be healthy part of one’s diet.” While she shares the Paleo crowd’s concern about modern convenience foods and sweets, she is also worried about our present-day gluttony. “I think processed food deserves the criticism, but probably not because we haven’t evolved; more likely because we eat too much of it and most of it is nutritionally void.”

Andrus suggests a common-sense strategy, one that Kresser says in his book he can endorse. “Some people like to abide by the 80/20 rule; if 80% of your diet is perfect, there’s wiggle room for the rest,” she says. After all, “There’s a lot of space between Paleo and a crappy diet of Pop-Tarts and McDonald’s.”