New Science on How We Burn Calories
It’s simple, we’re often told: All you need to do to maintain a healthy weight is to consume as many calories as you consume. If you take in more calories, or energy, than you use, you gain weight; If the output is greater than the input, you lose it. But while we’re often conscious of burning calories while we exercise, 55 to 70 percent of what we eat and drink actually goes to fuel all the invisible chemical reactions that happen in our bodies to keep us alive. . “We think of metabolism as just about exercise, but it’s much more than that,” says Hermann Pontzer, associate professor of evolutionary anthropology at Duke University. “It’s really going to be how busy your cells are throughout the day.” Figuring out your total energy expenditure tells you how many calories you need to live. But it also tells you “how the body is functioning,” Ponzer says. “There is no more direct measure of this than energy expenditure.”
Although scientists have been studying metabolism for at least a century, they haven’t been able to measure it precisely—in real-world conditions, in enough people, over a wide-enough age range—to see if it How duration changes throughout human life. It is clear that the older someone is, the more cells they have, and thus the more total calories they burn per day. But it has become very difficult to assess whether variables such as age, gender, lifestyle and disease affect our rate of energy expenditure. This paucity of data led to assumptions rooted in personal experience: for example, the significant hormonal changes that occur during puberty and menopause speed up or slow down our metabolism, prompting us to burn more or fewer calories per day. is done; or that men naturally have a faster metabolism than women, as they seem to be able to shed pounds more easily; Or that our energy expenditure slows in mid-life, leading to a gradual and inevitable weight gain. “I’m in my 40s; I feel different than I did in my 20s—I buy into that too,” Pontzer says. “Not all that intuition was backed up by the data. It just seemed so convincing.”
Last month, however, a paper published in Science by Ponzer and more than 80 co-authors revealed that what we thought we knew about metabolism was wrong. Using previously collected data from more than 6,400 subjects, ranging in age from 8 days to 95 years, and adjusting for body size and amount of fat and muscle, they found that our metabolism generally Goes through four different life stages. The metabolism of newborn babies is similar to that of adults. Then, when they are about a month old, their metabolic rate begins to increase rapidly until, between 9 and 15 months, it exceeds that of an adult by more than 50 percent—more than that of an older person. The equivalent of burning about 4,000 calories a day. (The U.S. Department of Health and Human Services estimates that, on average, adult women need between 1,600 and 2,400 calories a day and adult men between 2,000 and 3,000 calories.) At that time, between 1 and 2 years of age. Meanwhile, energy expenditure begins to decline. and continues to decline till the age of about 20 years. From there, it remains constant for the next 40 years, even during pregnancy and menopause; You burn calories at 55 just as efficiently as you do at 25. Around the age of 60, energy expenditure starts decreasing again and continues to do so until the end of our lives. Men, the researchers observed, don’t have an innately faster metabolism than women; Instead, they burn more calories per day for their size because they generally have a higher proportion of muscle, which uses more energy than fat.
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