It’s a noble concept: Forgo the processed junk that modern Americans eat and opt for what our preagricultural forbears gobbled up instead. The diet has spawned myriad how-to books and websites denouncing a long and specific list of foods including dairy, legumes, wheat, and pseudo-cereal grains. But though Paleo eating has thousands of fans, the truth is that it just doesn’t hold up with historical data.

At least according to a study published this week in the Quarterly Review of Biology. Researchers from Georgia State University and Kent State University say there’s not one accurate “Paleo diet.”

They studied living animals’ feeding behavior and anatomical and paleoenvironmental data, and they found that although early primates had teeth unfit for many plants, they probably just ate anything that was available to them—much like bears and pigs. Cavemen who lived in the north, for instance, likely relied on a meat-heavy diet, but those near the equator probably had a plant-based diet. (A separate study found that rotten teeth of ancient hunter-gatherers indicate that they loaded up on carbs millennia before the cultivation of grain.)

“I think that you would certainly have lots of variation way beyond what [the Paleo diet’s] recommendations are,” Ken Sayers, a researcher from Georgia State, said in a statement. “When you’re trying to reconstruct the diet of human ancestors, you want to look at a number of things, including the habitats they lived in, the potential foods that were available, how valuable those various food items would have been in relation to their energy content, and how long it takes to handle a food item.”

Cain Credicott, the founder of Paleo Magazine, told ABC News that the diet is more “about nourishing our bodies with real food that is grown and raised as nature intended.”

But it might be too late for that. Sayers pointed out that even foods allowed in the Paleo diet bear little resemblance to what was available 10,000 years ago. Wild strawberries, for example, are bitter—much different than even the ones sold at Whole Foods.

“The foods that we’re eating today, even in the case of fruits and vegetables, have been selected for desirable properties and would differ from what our ancestors were eating,” said Sayers.

Plus, it’s hard to tell whether cavemen’s diets were that much healthier—they lived decades shorter than humans today. While the researcher concedes that what’s referred to as “diseases of affluence” have been linked to eating high-fat foods, he said that we might just be living long enough for these illnesses to show up.

To be sure, avoiding soda, French fries, and other processed foods is a smart way to keep healthy. But perhaps focusing on what our ancestors ate and going with a let-them-eat-grass-fed-steak approach isn’t the best strategy.

“Everyone would agree that ancestral diets didn’t include Twinkies,” said Sayers, “but I’m sure our ancestors would have eaten them if they grew on trees.”