Relatively speaking, the giant panda’s bamboo-only preference may actually be a recently acquired fad diet, a new study shows.

Previous studies found that the giant panda, Ailuropoda melanoleuca, made the switch from being omnivorous to keeping a strictly bamboo diet long ago—with ancestral species adding bamboo to their diet about 7 million years ago and then going bamboo-exclusive about 2.4 to 2 million years ago. But new research suggests that’s not the case at all: Pandas turned to a bamboo-only lifestyle just 5,000 to 7,000 years ago, possibly under pressure from the encroaching human population, according to a new study in the journal Current Biology.

Pandas are a true black-and-white paradox. They have the physical structure of a carnivore and a gut that is optimized for digesting meat, but instead they chow down on bamboo. The problem is, they are not very good at digesting the stuff and don’t even have the right microbes to break it down, only extracting about 20 percent of the available energy from the plant. That means to get enough energy to survive they have to eat enormous quantities of the stuff all day, every day, for 12 to 16 hours. The only remaining places that can provide that much bamboo are a few high mountain forests in western China where about 1,860 of the animals remain in the wild.

Emiliano Rodriguez Mega at Nature reports that to understand exactly when pandas went full-bamboo, researchers from the Chinese Academy of Sciences analyzed the fossilized remains of 12 ancient pandas collected at seven archaeological sites in China as well as the bone collagen from pandas that lived between the 1970s and 2000s. They also looked at the bones of other mammals living in the same region.

While it’s not possible to figure out exactly what species of plant or animal an ancient critter ate, looking at the ratios of stable isotopes of carbon and nitrogen in their remains can reveal the broad strokes—like whether it was eating primarily meat or plants, or if it had a varied diet. Analyzing bones can show what the creature ate in the last few years of its life, while examining tooth enamel can reveal what it ate in its first few years. And weird diets—like exclusively eating bamboo—create unique patterns of isotopes.

The isotope analysis of the ancient pandas appears to show that as late as 5,000 years ago, giant pandas had a much more varied diet than their bamboo-chomping descendents. Jeremy Rehm at Science News reports that when the panda isotopes were compared to other herbivores from the same time period, they were indistinguishable, meaning the pandas were chowing down on more plants than just bamboo.

“It has been widely accepted that giant pandas have exclusively fed on bamboo for the last two million years,” co-author Fuwen Wei of Chinese Academy of Sciences says in a statement. “Our results showed the opposite.”

When, exactly, the pandas went from eating a wide variety of plants to just bamboo is difficult to pinpoint and will require finding more panda fossils.

“We need to get more samples from different years after 5,000 years ago, but it is hard to do this,” Wei tells Genelle Weule at the Australian Broadcasting Corporation.

Exactly why they switched to only bamboo is harder to determine. “[We] do not know the exact reasons,” Wei says. “Maybe it is a complicated [mix of] climate change, human encroachment and species competition for resources.”

Zoologist Huabin Zhao of Wuhan University tells Mega at Nature that understanding why the pandas restricted their range and their diet could help modern conservationists help save the animal, which is currently listed as vulnerable by the IUCN, which manages the world’s endangered species list. “If we know what kinds of changes have reduced the habitat of giant pandas, [we could] create better conservation strategies,” Zhao says.

Currently, the best conservation strategy is to provide the pandas with more land in the form of unfragmented bamboo forests with limited human encroachment. After Chinese government panda reserves were cut by almost three quarters in the 1980s, panda populations dropped by half. Since then, an increase in panda land and a massive spike in global interest in the species has helped its population to double to 1,864.

In 2016, the species was downgraded from endangered to vulnerable, though threats remain, including increased habitat fragmentation and more human encroachment into the mountains where they spend long, long days nibbling their favorite—and really only—treat.