A study published on May 4 in the journal Nature states that we have higher metabolism rates than our primate relatives, enabling us to evolve bigger brains. The findings confirm an earlier theory that faster metabolism and a larger energy budget are needed to accommodate big brains.

Because of the fast metabolism rates, humans are predisposed to have a higher percentage of body fat. According to Loyola University Chicago researchers, further human metabolic measurement toward this may lead to better treatments that will combat obesity.

The research team observed that humans take in 635 calories more than gorillas, 400 more calories than chimpanzees and bonobos and 820 more calories than orangutans. Over seven to 10 days, the researchers measured the total energy expenditure of 10 gorillas, 11 orangutans and 27 chimpanzees who were asked to stick to their normal everyday routine. A total of 141 people from South Africa, Ghana, Seychelles, Jamaica and the US were investigated in another study called Modelling the Epidemiological Transition Study (METS).


Humans have evolved bigger brains than close ape relatives due to higher metabolism rates. Credit: Raimee / Fotolia

The researchers used the doubly labelled water method to measure the energy expenditure, which involves total calories burned by metabolism when the body is at rest and the total calories burned during physical activity. Body fat was generally higher in the humans, specifically 22.9 percent and 41.7 percent body fat in men and women respectively.

Accordingly, these metabolic measurements of hominoids, the term used for the “superfamily” of humans and great apes, may provide clues to combat obesity and prevent other metabolic diseases that include¬†heart disease and diabetes. The researchers are now planning to conduct another study that will reveal the link between weight gain, physical activity, and energy expenditure.

“Humans exhibit an evolved predisposition to deposit fat whereas other hominoids remain relatively lean, even in captivity where activity levels are modest,” states the study. “Untangling the evolutionary pressures and physiological mechanisms shaping the diversity of metabolic strategies among living hominoids may aid efforts to promote and repair metabolic health for humans in industrialised populations and apes in captivity.”