If you want to eat like your paleo ancestors, stop cutting out all carbs, a new study suggests

• Some research has suggested that eating meat helped early humans' brains evolve to be larger.
• So dieters seeking to emulate their ancestors usually rely on meat-heavy, low-carb diets like keto.
• But a new study suggests Neanderthals and their ancestors ate plenty of starchy carbohydrates.

Images of our human ancestors in popular culture often depict muscly hunters chasing and feasting on big game. So it makes sense that contemporary imitators follow diets like Paleo and keto that are meat-heavy and low-carb.

But new evidence suggests that Neanderthals and their ancestors consumed hefty portions of starchy carbohydrates as they expanded across eastern Africa and into Europe.

Traces of ancient bacteria on Neanderthal teeth suggest that starting at least 600,000 years ago, our ancestors ate carb-rich plant foods to meet the energy demands of increasingly bigger brains. That's according to a study published Monday from a team including anthropologists at Harvard University and the Max Planck Institute in Germany.

"It's clear early humans hunted, but I think it's nearly impossible they were exclusively hunting. And I think it's really improbable that they were even predominantly hunting," Christina Warinner, a Harvard anthropologist and co-author of the new study, told Insider. "I think they had a mixed dietary strategy."

So modern-day dieters trying to emulate our ancestors' habits by prioritizing meat are missing the mark: "'The Paleo diet' is really quite unrelated to the Paleolithic," Warinner said. "It's a misnomer."

Our ancestors' teeth can reveal what they ate

The earliest members of the genus that includes modern humans, Homo, first appeared during the Paleolithic period, which began 2.5 million years ago. Eventually, they displaced the human ancestors before them, the Australopiths.

Australopiths had tiny brains similar in size to those of chimpanzees. By the time Neanderthals appeared at the end of the Paleolithic period, about 12,000 years ago, our ancestors' brain size had tripled.

Initially, anthropologists thought that meat-eating was what prompted early human brains to grow rapidly, since some research suggests Neanderthals' primary food source was meat. But Warinner was skeptical: Growing brains require glucose, a simple sugar gleaned from carbohydrates. There isn't much glucose in meat.

What's more, many studies on Neanderthals' meat consumption relied on the ratio of carbon and nitrogen in their teeth and bones, but factors other than diet - including periodic fasting - can influence that measurement.

So Warinner's team looked at the DNA of bacteria fossilized onto ancient teeth. They compared tooth bacteria from 124 living and extinct primates, including a Neanderthal that lived 100,000 years ago in Europe. The results showed that Neanderthals had almost the exact same bacteria in their mouths as modern humans do.

One bacteria subspecies in particular caught the researchers' eyes because it can feed itself using an enzyme in our saliva called amylase. Amylase is what helps our bodies extract sugar from starchy tubers and roots.

That bacteria was only present on human and neanderthal teeth - not teeth from chimps, gorillas, or howler monkeys.

"It gives us some hints that starch was present in the early human diet," Warinner said.

The finding also suggests that early humans commonly cooked food over a fire, she added, since the amylase enzyme is better at breaking down starches when they're cooked.

The Paleo and keto diets may not resemble those of our ancestors

The new findings fly in the face of the popular Paleo diet, which relies heavily on meat, fish, and greens while eschewing grains and starches.

The ketogenic diet is even more restrictive, severely limiting carbohydrates in favor of fat and protein, often from meat.

Low-carb diets like these prompt the body to produce its preferred fuel, glucose, in the liver and kidneys, using components of fat and protein in a process called gluconeogenesis. Another low-carb metabolic strategy is ketosis, a state where the body adapts to fuel the brain and other organs by burning fat instead of glucose.

But Warinner doesn't think early humans relied on gluconeogenesis or ketosis.

"Making your own sugar, producing your own glucose, actually requires a high amount of dietary fat," she said.

Most of the terrestrial animals that the ancestors of Neanderthals hunted in Africa did not have large fat stores, Warinner added.

"Populations that have survived for a very long period of time on low carbohydrate diets, they tend to be marine mammal hunters, because marine mammals have large fat stores," she said.

Ultimately, comparing today's diets with ancestral ones is a fallacious exercise, since modern-day humans live in a world nothing like that of Neanderthals.

"Someone who sits at a computer for eight hours a day, you know, they live a different life than someone who is foraging," Warinner said.

The starchy tubers our ancestors ate were also different than contemporary carbs - they were nutrient-dense, high in fiber, and rich in vitamins.

"It's not really fair to compare wild root vegetables with things like pizza and pasta," Warinner added. "They're really different in their nutritional makeup and composition."

There's little evidence that the Paleo or keto diets offer strong advantages over other nutrient-rich, whole-food eating styles.

"I don't think we need to throw everything back and dial the clock back 10,000 years to be healthy," Warinner said.