A large study that measured the total amount of energy that people expend as they go about their everyday lives has opposed the idea that metabolism slows in middle age.
The study showed that total energy expenditure, adjusted for body size, steadily declines from a peak in infancy until around 20 years of age and then remains stable until about 60. Only then does energy use begin to fall again. The researchers were surprised to discover that, for their size, 1-year-olds burn calories 50% faster than adults.
“Of course they’re growing, but even once you control for that, their energy expenditures are rocketing up higher than you’d expect for their body size and composition,” says one of the researchers, Dr. Herman Pontzer, associate professor of evolutionary anthropology and global health at Duke University in Durham, NC.
There are several physiological turning points associated with growing older, says Dr. Pontzer, including puberty and menopause. “What’s weird is that the timing of our ‘metabolic life stages’ doesn’t seem to match those typical milestones,” he says.
Another surprise was how little energy expenditure changes from early adulthood through middle age. “Perhaps the most unexpected feature was the constancy of metabolic rate in both males and females between the ages of 20 and 60,” tweeted co-author Dr. John Speakman, of the University of Aberdeen in the United Kingdom.
“This suggests that if you are experiencing middle-age spread, it’s more likely to be because you are eating more rather than expending less,” he added.
The research appears in the journal Science.
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