PORTLAND, Ore. (KOIN) – Feeding bears in zoos like they are high-protein carnivores will kill them slowly, according to a new report from Washington State University wildlife biologists. 

The new study, published Sept. 9 in Scientific Reports, explains that bears are omnivores like humans and need a lot less protein than they are typically fed in zoos. 

Researchers found that when given a choice, captive bears will mimic the mixed diets of their wild peers. 

In separate experiments, researchers gave giant pandas and sloth bears at different U.S. zoos unlimited, different types of food to see what they prefer. 

Researchers found that giant pandas at the Memphis Zoo preferred the carbohydrate-rich culm in the woody bamboo stalks over the more protein-rich leaves. At some points, the pandas almost exclusively ate the stalks. 

Biologists also analyzed data from five Chinese zoos that had successfully reproduced and found that these pandas also preferred a high-carbohydrate, low protein diet. 

At the Cleveland, Little Rock and San Diego zoos, scientists performed a similar experiment on six sloth bears. They were presented with unlimited avocados, baked yams, whey and apples. They chose the fat-rich avocados almost exclusively. Their diet consisted of about 88% avocados to 12% yams. They ignored the apples altogether. 

This preference for a high-fat, low carbohydrate diet may have a similar makeup to the sloth bear’s wild diet of termites and ants, as well as their eggs and larvae, WSU said. 

This diet is vastly different from the high-carbohydrate diet sloth bears are usually fed in activity. 

Sloth bears typically live for around 17 years in U.S. zoos, but WSU said this is almost 20 years less than the maximum lifespan they should be able to achieve in human care. Their most frequent cause of death is liver cancer. 

In a paper published in November 2021, WSU researchers saw a similar pattern in polar bears. They found captive polar bears would prefer a fat-rich diet like that of wild polar bears instead of the high-protein diet they’re normally fed in zoos, if given the choice. 

Polar bears in zoos typically die about 10 years earlier than they should, most often of kidney and liver disease, WSU said. 

These two diseases can develop from long-term inflammation of the kidney and liver. The inflammation could potentially be caused by many years of poorly balanced diets, researchers said. 

“There’s certainly this long-standing idea that humans with Ph.D.s know a lot more than a sloth bear or a brown bear,” said Charles Robbins, a WSU wildlife biology professor and lead author of the study. “All of these bears started evolving about 50 million years ago, and in terms of this aspect of their diet, they know more about it than we do. We’re one of the first to be willing to ask the bears: What do you want to eat? What makes you feel well?” 

Robbins founded the WSU Bear Center. It’s the only research institution in the U.S. with a captive population of grizzly bears. He’s studied bear nutrition for decades and he and his graduate students first started investigating their mis-balanced diets during a study in Alaska. 

While in Alaska, the researchers predicted the grizzlies would gorge themselves on salmon, sleep, and then wake up to eat more salmon. 

Instead, the bears surprised them. They would eat salmon, but then spend hours finding and eating small berries. This led to Robbins’ laboratory investigating the diet of the grizzly bears at the Bear Center. They found the bears gained the most weight when fed a combination of protein, fats and carbohydrates in the form of salmon and berries. 

“It just opens up so many more food resources than just being a straight, high protein carnivore,” Robbins said.

All eight types of bears had a carnivore ancestor, but have since evolved to eat a wide variety of food. This allowed them to spread into more areas by not directly competing for food with other resident carnivores.