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Researchers have finally found out the reason behind big brains in human beings. According to a new study conducted by Loyola University Chicago researchers, human beings have bigger brains than other closely related apes all thanks to their faster metabolism rate.

Metabolism refers to biochemical processes through which our body burns calories. A better metabolism leads to better development of the brain. The study found that human beings have a faster metabolism rate than closely-related primates. Humans have more body fat, which provides the energy reserves needed to fuel that faster metabolism.

"Every gram of brain uses an enormous amount of calories," said Herman Pontzer, the first author on the study at Hunter College in New York, reported The Guardian. "The fat is your reserve tank to help fuel this metabolic engine that we have revved up compared to the other apes," Pontzer added.

For the study, the research team compared the metabolic rates of 141 humans to 27 chimpanzees, 11 orangutans, 10 gorillas and eight bonobos. Total energy expenditure was measured over seven to 10 days while the apes and humans followed their normal routines.

Human data was derived from a separate study called the Modeling the Epidemiological Transition Study (METS), which included participants from the U.S., South Africa, Ghana, Seychelles and Jamaica. Taking into account body size, it was found that humans on a daily basis burn 400 more calories than chimpanzees and bonobos, 635 more calories than gorillas and 820 more calories than orangutans.

Body fat percentage in humans was found to be significantly higher than other apes. While, males have an average of 22.9 percent body fat, women have 41.7 percent body fat as compared to 15.2 percent body fat in male gorillas and 13.9 per cent in female gorillas.

"Humans exhibit an evolved predisposition to deposit fat whereas other hominoids remain relatively lean, even in captivity where activity levels are modest," the researchers noted in the study paper, reported HNGN. "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 industrialized populations and apes in captivity."

Although the study findings seem promising, more research on the issue is required since the research was performed only on adults. The research findings have been published in the May 4 issue of the journal Nature.