Humans, primates burn 50 percent fewer calories than other animals, study finds - Science Recorder

According to a January 13 news release from the Lincoln Park Zoo, a new study conducted by an international team of scientists found that humans and other primates 50 percent fewer calories per day than other animals. The study appears in the latest edition of the Proceedings of the National Academy of Sciences, and posits that this comparatively slow metabolic rate may account for why humans and other primates grow up so slowly and live such long lives. Additionally, the study found that primates in captivity use as much energy each day as they do in the wild, which also suggests that physical activity may have less of an effect on daily energy use than previously believed.

Humans and our primate relatives have long childhoods, have children infrequently, and live remarkably long lives. The slow pace of life exhibited by primates has long mystified biologists because the mechanisms underlying it were unknown.

The international team at the heart of the study examined daily energy expenditure in 17 primate species, from gorillas to mouse lemurs, to assess whether primates' slow pace of life results from a slow metabolism. By using a safe and non-invasive technique known as "doubly labeled water," the researchers measured the number of calories that primates burned over the course of 10 days. Then, by combining these measurements with analogous data from other studies, the team compared daily energy expenditure amongst primates to that of other mammals.

"The results were a real surprise," said Herman Pontzer, an anthropologist at Hunter College in New York and the lead author of the study. "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 enormous decrease in metabolism accounts for the primates' slow pace of life. "The environmental conditions favoring reduced energy expenditures may hold a key to understanding why primates, including humans, evolved this slower pace of life," said David Raichlen, an anthropologist at the University of Arizona, and a coauthor of the study.

Surprisingly, the team's measurements illustrate that primates in captivity expend as many calories each day as their feral counterparts.

"The completion of this non-invasive study of primate metabolism in zoos and sanctuaries demonstrates the depth of research potential for these settings," said coauthor Steve Ross, Director of the Lester E. Fisher Center for the Study and Conservation of Apes at Chicago's Lincoln Park Zoo.

The conclusions reached during this study portend interesting implications for understanding health and longevity in humans. Connecting the rate of growth, reproduction, and aging to daily energy expenditure may illuminate the processes by which humans develop and age.

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