Bears, like humans and other primates, are omnivores and require far less protein than many zoos feed them. Excess protein is linked to a higher risk of kidney issues and can shorten the lifespan of crop plants. This relationship also appears to affect humans, based on current evidence.
A recent study published in Scientific Reports from Washington State University adds to this understanding, focusing on the nutritional needs of giant pandas and sloth bears. An accompanying study in Zoo Biology, published a few months earlier, arrived at the same conclusions for polar bears.
Bears, unlike cats, are not strict carnivores. A wildlife biology professor at Washington State University, who led both studies, cautions zoo staff against the common mistake of feeding bears protein-rich diets modeled on carnivores.
Whether polar bears, grizzly bears, or sloths, the advice has traditionally been to provide protein-heavy diets. When that happens, health can suffer over time, Robbins emphasizes.
In the latest work, researchers ran separate experiments with giant pandas and sloths housed at different U.S. zoos. Animals could access unlimited food of various kinds to reveal their preferences, and the team documented the nutritional profiles of what the animals chose.
Collaborating with researchers from Texas A and M University and the Memphis Zoo, the team conducted nutritional tests on two pandas to gauge how they select bamboo. The discovery was striking: the pandas favored stems rich in carbohydrates that come from woody parts, while leaves offered higher protein.
liver cancer
There were periods when pandas consumed almost exclusively culm, or airborne stems, such as March, when this pattern was most evident. Data from five Chinese zoos with giant pandas also indicated a high-carbohydrate, low-protein dietary tilt.
Meanwhile, six sloths in Cleveland, Little Rock, and San Diego zoos were given unlimited avocados, baked sweet potatoes, buttermilk, and apples. They overwhelmingly chose high-fat avocados, consuming about 88 percent avocados to 12 percent sweet potatoes, and largely ignored apples.
This demonstrates that sloths prefer a high-fat, low-carb diet similar to what they eat in the wild, which includes termites, ants, eggs, and larvae. Their choices diverged markedly from the high-carb diet often provided in captivity.
Researchers have linked these dietary patterns to life expectancy. Native to India, sloth bears typically live around 17 years in zoos, roughly 20 years less than the potential lifespan in the wild or under ideal care. Liver cancer is the most common cause of death in these animals.
In polar bears kept in zoos, lifespan can also shorten by about a decade, with kidney and liver diseases frequently arising from long-term nutritional imbalances that are not well balanced for captive diets.
50 million years of evolution
In captivity, polar bears are often fed a diet similar to that given to big cats, with about two parts protein to one part fat. That ratio contrasts with what their wild counterparts consume. Yet across studies, captive bears tend to select foods that resemble what free-living bears eat when given a choice.
There is a shared voice among researchers that bears have adapted over roughly 50 million years to a broader range of foods than strict carnivory would allow. This omnivorous flexibility opens up many food sources and reduces direct competition with resident carnivores. Robbins notes that bears know more about their own dietary needs than humans realize, highlighting the value of listening to what the animals choose to eat.
Further context for these findings comes from the Nature Scientific Reports study and a polar bear feeding report. These reports underscore the importance of aligning captive diets with the natural feeding patterns observed in wild populations.
Additional notes for readers interested in the broader scientific context include the work with researchers from leading institutions and the ongoing efforts to refine nutrition in captive bear populations.
The evolution of these ideas is rooted in long-term observational work. Robbins and his team began by watching grizzly bears in Alaska as they foraged for salmon and berries, challenging the old belief that salmon alone would drive their feeding. The actual pattern showed a more nuanced balance of protein, fat, and carbohydrates that better explains weight changes and overall health in captivity.
Robbins, founder of the Bear Center, describes how this line of inquiry grew from a simple curiosity about what bears eat to a broader understanding of how diet influences health and longevity in captive settings. The research suggests that omnivory offers a wider palette of foods, supporting healthier outcomes than a rigid, high-protein carnivore model.
References to the broader literature and ongoing work emphasize the shift away from one-size-fits-all diets in zoos toward nutrition that mirrors the animals’ natural feeding choices.
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Laws, regulations, and practical guidelines regarding bear nutrition continue to evolve as new evidence emerges, with the ultimate goal of promoting welfare and extending healthy lifespans for captive bears.