Humans have higher metabolic rates than other mammals

Using a new comparison method that they say better corrects for body size, ambient temperature and body fat, the researchers found that unlike most mammals, including other primates, humans have evolved to accommodate a compromise between rest and activity Metabolic rates escaped.

Animals take in calories through food and spend them like a bank account on expenses that are mostly divided into two broad metabolic categories: rest and physical activity. In other primates, there is a clear trade-off between resting and active metabolism rates, which explains why chimpanzees, with their large brains, costly reproductive strategies and lifespans, and thus high resting metabolism, are “couch potatoes” who spend much of their time eating daytime meals, Lieberman said.

In general, the energy that animals spend on metabolism is converted into heat, which is difficult to dissipate in warm environments. Because of this trade-off, animals such as chimpanzees, which expend a lot of energy on their resting metabolism and also live in warm, tropical environments, must maintain low activity levels.

“Not only have humans increased their resting metabolism, something even chimpanzees and monkeys have done, but – thanks to our unique ability to dissipate heat through sweating – we have also been able to increase our physical activity without lowering our resting metabolism. said co-author Andrew Yegian, a senior researcher in Lieberman’s lab.

“The result is that we are an energetically unique species.”

The team’s analysis shows that monkeys and great apes have evolved to invest about 30 to 50 percent more calories in their resting metabolism than other mammals of the same size, and that humans have exacerbated this even further, adding 60 percent more calories invested than comparable mammals. large mammals.

“We started by asking whether it was possible that humans and other primates could have comparatively low total metabolic rates, as other researchers had suggested,” Yegian said. “We tried to find a better way to analyze it using quotients. We’ll step on the gas.”

The research team – which includes collaborators from the Pennington Biomedical Research Center in Louisiana and the University of Kiel in Germany – plans to further investigate metabolic differences between human populations. For example, subsistence farmers, who grow all of their food without the aid of machinery, have significantly higher levels of physical activity than both hunter-gatherers and people in industrial environments such as Americans. However, all human populations, regardless of activity level, expend similar amounts of energy on their resting metabolism relative to their body size.

“What we’re really interested in is the variation in metabolic rates between people, particularly in today’s world of increasing technology and reduced physical activity,” Yegian said. “How does a desk job change our metabolism in ways that affect health since we evolved to be active?”

Reference: Yegian AK, Heymsfield SB, Castillo ER, Müller MJ, Redman LM, Lieberman DE. Metabolic scaling, energy allocation trade-offs, and the evolution of humans’ unique metabolism. PNAS. 2024;121(48):e2409674121. doi: 10.1073/pnas.2409674121

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