The researchers found the panda's microorganisms much more closely resembled those of other carnivores and omnivores, and were missing the bacteria that helps other animals digest plant fiber, suggesting they're still not adapted to eating bamboo.
The process is so inefficient that while panda spend up to 14 hours per day chowing down on bamboo, they only digest about 17% of it.
But some scientists call that conclusion into question.
Puzzling research suggests pandas can't digest their favorite food
One-year-old female giant panda cub Nuan Nuan reacts inside her enclosure during joint birthday celebrations for the panda and its ten-year-old mother Liang Liang at the National Zoo in Kuala Lumpur on August 23, 2016. Giant pandas Liang Liang, aged 10, and her Malaysian-born cub Nuan Nuan, 1, were born on August 23, 2006 and August 18, 2015 respectivetly.
(MOHD RASFAN/AFP/Getty Images)
A zoo employee holds three-month-old female giant panda cub, born to mother Liang Liang and father Xing Xing, on display to the public for the first time at the national zoo in Kuala Lumpur, Malaysia, November 17, 2015.
Newborn giant panda triplets, which were born to giant panda Juxiao (not pictured), are seen inside an incubator at the Chimelong Safari Park in Guangzhou, Guangdong province August 17, 2014. According to local media, this is the fourth set of giant panda triplets born with the help of artificial insemination procedures in China, and the birth is seen as a miracle due to the low reproduction rate of giant pandas. Picture taken August 17, 2014.
A baby panda plays in a enclosure at the Giant Panda Research Base in Chengdu, southwest China's Sichuan province on June 24, 2012, as thousands of visitors gather for the Duanwu festival or better known as the Dragon Boat festival. China engages in 'panda diplomacy', using the endangered but iconic bears as diplomatic gifts to other countries, and also runs a lucrative trade hiring the animals out to foreign zoos, as only around 1,600 remain in the wild in China, with some 300 others in captivity.
Giant panda Hao Hao eats bamboo leaves in its pen at Pairi Daiza animal park in Brugelette on April 15, 2014.
(JOHN THYS/AFP/Getty Images)
This picture taken on September 23, 2013 shows new-born panda cubs displayed on a crib during a press conference at the Chengdu Research Base of Giant Panda Breeding in Chengdu, southwest China's Sichuan province. 14 giant panda cubs born in 2013 were presented to the public at the press conference, during which the research base introduced the global breeding situation of giant pandas this year.
EDINBURGH, SCOTLAND - APRIL 10: Yang Guang, the male Panda at Edinburgh Zoo, eats bamboo inside his enclosure on April 10, 2013 in Glasgow, Scotland. Zoo experts can now say that the giant pandas Tian Tian and Yang Guang are likely to meet for the breeding season imminently. The Royal Zoological Society of Scotland has announced that scientific testing has identified that female panda Tian Tian could possibly now be as little as 10 days away from her 36 hour fertile window.
(Photo by Jeff J Mitchell/Getty Images)
A Panda Bear in the Olympic Games Panda Bear enclosure at the Beijing Zoo on May 22, 2012. The zoo grounds were originally a Ming Dynasty imperial palace and finally opened to the public in 1908. The zoo's history states that during the WWII, most of the zoo's animals died of starvation with only 13 monkeys and one old emu surviving the war.
Giant panda Juxiao plays with her cub, one of the panda triplets at Chimelong Safari Park on December 9, 2014 in Foshan, China. The world's only live giant panda triplets (two boys and one girl) started living together with their mother, giant panda Juxiao, after taking turns living with her since their birth at the Chimelong Safari Park on Tuesday. The triplets were born on July 29 and after over 100 days they now all weigh over 8 kg and are doing well. They will stay with their mother and meet with visitors at 13:00 - 15:00 and 16:00 - 18:00 from Tuesday.
(Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)
This picture taken on July 17, 2014 shows giant panda Ai Hin holding a bamboo twig at the Chengdu Giant Panda Breeding Research Centre in Chengdu, in southwest China's Sichuan province. Hopes that tiny panda paws would be seen in the world's first live-broadcast cub delivery were dashed on August 26, 2014 when Chinese experts suggested the 'mother' may have been focusing more on extra bun rations than giving birth.
A worker shows of one of the baby pandas at the Giant Panda Research Base in Chengdu, southwest China's Sichuan province on June 24, 2012, to attract visitors for the Duanwu festival or better known as the Dragon Boat festival. China engages in 'panda diplomacy', using the endangered but iconic bears as diplomatic gifts to other countries, and also runs a lucrative trade hiring the animals out to foreign zoos, as only around 1,600 remain in the wild in China, with some 300 others in captivity.
A feeder moves a giant panda cub in an enclosure as the panda triplets make their debut appearances to the public to celebrate their 100th days after birth, at Chimelong Safari Park in Guangzhou, Guangdong province November 5, 2014. The triplets was given birth by giant panda Juxiao (not pictured) at the park in July. The birth is seen as a miracle due to the low reproduction rate of giant pandas.
Giant Panda cub Fu Bao, meaning lucky leopard, sits on a tree stump in its enclosure at the zoo in Vienna January 10, 2014. It is the Panda's second public appearance outside of its tree cave since it's birth on August 14, 2013.
Two-year-old giant female panda Bao Bao licks honey off of a plastic crate after a press conference to announce the gender and paternity of the giant panda cub twins recently born to female panda Mei Xiang, at the zoo in Washington, D.C., Friday, August 28, 2015. Both the surviving and deceased twins are male and the father is Tian Tian, sharing parents with Bao Bao.
(Photo by Allison Shelley/For The Washington Post via Getty Images)
Seven-month old female giant panda cub Nuan Nuan plays with her mother Liang Liang at the National Zoo in Kuala Lumpur on April 7, 2016.
(Photo by Mohd Daud/NurPhoto via Getty Images)
Bing Xing, father of Chulina, a female panda baby, that was born last August, eats bamboo side its enclosure at a zoo in Madrid, Spain, January 12, 2017.
A giant panda 'Bing Xing', who is father of female panda 'Chulina', which was born last August in Madrid, is seen at the zoo in Madrid, Spain on January 12, 2017.
(Photo by Senhan Bolelli/Anadolu Agency/Getty Images)
Baby panda Fu Wa, its same name with Beijing Olympics' mascot, attends a ceremony at China Conservation and Research Centre for the Giant Panda in Wolong, in China's south western province of Sichuan, 10 February 2007. The ceremony marks the occasion of the 18 panda cubs which were all born in 2006 and been weaned and step into the garden of a nursery.
(LIU JIN/AFP/Getty Images)
'Kai Kai', a male panda from China, walks around its enclosure during a media preview at the River Safari on October 29, 2012. Two giant pandas, aged four and five-years old and on loan from China for 10 years to the Wildlife Reserve Singapore (WRS) - the parent company to the city's Jurong Bird Park, Night Safari and Singapore Zoo, are being housed in a custom-built 16,145 square foot enclosure costing 6.9 million USD within WRS's newest attraction, the River Safari, will open to the public for a special preview on November 29.
(ROSLAN RAHMAN/AFP/Getty Images)
Giant Panda, Kai Kai is seen in the Giant Panda enclosure during a media tour ahead of the opening of River Safari at the Singapore Zoo on March 25, 2013 in Singapore. The River Safari is Wildlife Reserves Singapore's latest attraction. Set over 12 hectares, the park is Asia's first and only river-themed wildlife park and will showcase wildlife from eight iconic river systems of the world, including the Mekong River, Amazon River, the Congo River through to the Ganges and the Mississippi. The attraction is home to 150 plant species and over 300 animal species including 42 endangered species. River Safari will open to the public on April 3.
(Photo by Chris McGrath/Getty Images)
A 5 1/2-month-old male panda named Xiao Liwu has its head measured during its weekly checkup at the San Diego Zoo on January 15, 2013. The 14-lb animal is still nursing and just learning to munch on a slice of apple. The healthy panda was born here at the zoo and along with it's mother has been on display for a limited number of hours since last week.
(Photo by Don Bartletti/Los Angeles Times via Getty Images)
Giant Panda Mei Xiang guards her fruit-filled bucket of ice at Washington's National Zoo where she and mate Tian Tian were having a birthday party. Mei Xiang was born July 22, 1998 and Tian Tian was born Aug. 27, 1997. But sharing a party seemed the diplomatic thing to do in the nation's capital.
(Photo by Harry Hamburg/NY Daily News Archive via Getty Images)
Eisen argues the scientists only looked at what microorganisms were found in the panda, and not what functions they actually carry out in the panda's digestive system.
Scientists theorize pandas started eating bamboo when they first moved to the higher elevation of the Chinese mountains where they live today, as a way of avoiding competition for prey with the predators already established there.
Like most bears, pandas are actually omnivores, and while they mostly eat bamboo, they will also eat meat if presented with it.