SAN DIEGO (Reuters Health) - We could learn a thing or two about staying in shape from the wild animals we love to watch on Animal Planet or the Discovery channel: They burn at least twice as many calories a day as we do, study findings show.

Though health experts often cite reduced physical activity levels among people in developed nations as one of the main contributors to the rising problem of obesity, it has been unclear just how sedentary people have become, said study author Dr. Steven Heymsfield, deputy director of the Obesity Research Center at St. Luke's-Roosevelt Hospital in New York.

So he and colleagues compiled data from many previous studies that assessed the energy expenditure of people as well as a variety of wild mammals, including orangutans, wolves, wildcats, bats, jack rabbits, squirrels and mice.

"We wanted to get an idea of what physical activity levels were like before we were 'domesticated,"' Heymsfield told Reuters Health. "We figured that animals living in the wild have physical activity levels similar to primitive humans."

The data suggest that modern-day humans in developed nations are considerably less active than generations past who had to scrape and scrounge for food and fight off predators, just as wild animals still do.

"In most wild mammals, for every calorie they burn at rest during the day, they burn another calorie or two in physical activity," Heymsfield said. "In people who are typical city dwellers, for every calorie they burn at rest, they burn only half a calorie in physical activity. That's half or less than half of the calories that mammals burn in the wild."

However, the study also found that some groups of people--athletes and army recruits--burn almost as much energy a day as animals, a level that is probably consistent with early humans, the researchers said.

Study results were presented here Sunday at a nutrition conference organized by the American Society for Clinical Nutrition and other medical groups.

Statistics show that more than half of US adults are overweight--an all-time high, according to the Centers for Disease Control and Prevention in Atlanta, Georgia.

"These new findings are one reason why the weights of people are moving upward," Heymsfield said.

But don't assume from the study that Fido and Fluffy are necessarily in any better shape than their owners. Heymsfield said domesticated animals are prone to a sedentary lifestyle as well, and many have the potbellies to prove it.

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