The Metabolism Myth

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You’ve likely heard, or maybe even said yourself, the phrase, “My metabolism is slowing down.” This common belief provides a convenient excuse for our expanding waistlines for those of us reaching our middle-aged years.

However, a recent study suggests that this age-old adage about our metabolism may be a myth. The study, published in August 2021 in the journal Science, examined the energy expenditure rates, or metabolism, of 6,421 people from 29 countries who ranged in age from eight days to 95 years old. As a result of the study’s depth and breadth, it provided one of the most precise pictures of what our metabolisms do as we age.

The researchers were able to measure people’s metabolisms using a method known as “doubly labeled water.” They had the subjects drink a water cup containing non-radioactive isotopes and then measure how quickly the isotopes leave the body in the urine.

What does our metabolism really do?

The metabolism rate grows rapidly from birth through the first year of life, peaking at year one. Then it steadily declines until a person reaches their early 20s. Puberty did not boost metabolism, which came as a surprise to the researchers. Instead, metabolism continued to decline steadily throughout adolescence.

Perhaps the biggest surprise of the study was that metabolism didn’t continue to drop after the 20s. Rather, it stayed stable until around age 60 in most subjects in the study, before beginning to decline again in later life. This research essentially puts to bed the notion that slowing metabolism is the reason for weight gain in our midlife years. 

Why do we gain weight?

The old “slowing metabolism” tale is a convenient scapegoat for our weight gain as we age, says Michelle Pearlman, M.D., a gastroenterologist with the University of Miami Health System. But, the reality is usually much more complex. “Age by itself is not the reason for weight gain, but other external factors at different ages have a larger contribution,” she says. 

Some of those factors may include:

  • Stress 
  • Poor sleep 
  • Medications 
  • Sedentary jobs 
  • Less planned exercise 
  • Eating large meals prior to bed
  • Alcohol
  • Eating on the run
  • Less time to eat meals while at work
  • Multi-tasking 

Maintain a healthy weight in a healthy way

Some supplements claim to boost your metabolism, and caffeine has been shown to cause a slight increase in metabolism, as well. However, the Mayo Clinic notes that a higher metabolism is not the key to losing weight or maintaining a healthy weight. Not surprisingly, the keys in this area are reducing calorie consumption and increasing activity. 

“As our bodies change, our nutrition and exercise need to adapt and change, as well,” says Dr. Pearlman. “It’s important to engage in weight-bearing exercises to maintain healthy bone density, as well as maintain our muscle mass. Lean body mass (muscle) plays a large role in our energy expenditure. If you are more sedentary or are on medications that promote weight gain, you must also alter your eating habits to account for those changes.” 


Wyatt Myers is a contributing writer for UMiami Health News.


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