Primates (inlcuding humans) have slower metabolisms than the rest of the animal kingdom, and it could explain the secret to their longevity.
Our metabolisms burn about 50 percent fewer daily calories than other mammals. A research team also noticed monkeys in captivity expend the same amount of energy as their peers in the wild; this suggests daily physical activity has less to do with energy expenditure than was previously believed, a Lincoln Park Zoo news release reported.
Most mammals grow up faster and live much shorter lives than humans and primates. Common pets such as dogs and hamsters reach adulthood in months and die by the time they reach their teens. Humans and primates reproduce less often than other animals, and have long childhoods and lives.
A research team looked at daily energy expenditure of 17 primate species in both the wild and captivity. The team was hoping to discover a link between longevity and a slower metabolisms.
The scientists employed a non-invasive technique called "doubly labeled water," this tracks the body's carbon dioxide production; the team was able to measure how many calories were burned in each subject over the course of 10 days.
"The results were a real surprise," Herman Pontzer, an anthropologist at Hunter College in New York and the lead author of the study, said. "Humans, chimpanzees, baboons, and other primates expend only half the calories we'd expect for a mammal. To put that in perspective, a human -- even someone with a very physically active lifestyle -- would need to run a marathon each day just to approach the average daily energy expenditure of a mammal their size."
This was the first time scientists had noticed this reduction in metabolic rate in primates. Energy expenditure is linked to aging; the primates' exceptionally slow metabolisms and long lives may have been shaped by evolution.
"The environmental conditions favoring reduced energy expenditures may hold a key to understanding why primates, including humans, evolved this slower pace of life," David Raichlen, an anthropologist at the University of Arizona and a coauthor of the study, said.
The finding that monkeys living in zoos burn just as many calories as those in the wild has important implications on the effects of physical activity.
"The completion of this non-invasive study of primate metabolism in zoos and sanctuaries demonstrates the depth of research potential for these settings. It also sheds light on the fact that zoo-housed primates are relatively active, with the same daily energy expenditures as wild primates," coauthor Steve Ross, Director of the Lester E. Fisher Center for the Study and Conservation of Apes at Chicago's Lincoln Park Zoo, said. "Dynamic accredited zoo and sanctuary environments represent an alternative to traditional laboratory-based investigations and emphasize the importance of studying animals in more naturalistic conditions."
The finding could be used in the future to help researchers learn more about human obesity and aging.
"Humans live longer than other apes, and tend to carry more body fat," Pontzer said. "Understanding how human metabolism compares to our closest relatives will help us understand how our bodies evolved, and how to keep them healthy."
