Forget Everything You Know About Your Metabolism

By Amanda Roland

“My metabolism just isn’t what it used to be.” 

Remember when you could run a mile in seven minutes on your high school track team or play ball with your buddies every day and never get tired? As we get older, we assume that our metabolism declines exponentially with every passing year, but new research has proven otherwise. The results might surprise you. 

According to the Mayo Clinic, metabolism is defined as “the process by which your body converts what you eat and drink into energy.” It has been a long-held belief that our metabolism slows as we age, becoming less efficient at processing food and used as an explanation for us packing on the pounds. 

Turns out, the time in our lives when our metabolism is at its best is when we are babies. You might think that it doesn’t take much energy to be a baby – they do have it pretty easy. But by the time a new baby is one year old, they are burning calories 50% faster than adults, according to Pennington Biomedical Research Center. Babies do grow very quickly in their first year of life, which would account for some of the increased energy expenditure, but the verdict is still out on why their energy expenditure is so incredibly high for their body size. This perplexity continues to be researched. 

So what happens after we are babies? Until we are about 20 years old, our energy expenditure, also known as our metabolism, slows by 3% each year. After we turn 20, we hit a plateau for the next 30 or so years. Even things like growth spurts and pregnancy do not have a major effect on metabolic rates during this time. After you hit your 60s, metabolism starts to decline slowly by about 0.7% per year, according to the Pennington article. We call these the four stages of metabolism (see below). 

This new research proves to us that age alone might not be why you can’t run that mile or play ball like you used to. If you have the same metabolism in your 20s as you do in your 40s, then what gives? Is it because of genetics, lifestyle, daily habits or some other factor? 

“Aging goes hand in hand with so many other physiological changes that it has been difficult to parse what drives the shifts in energy expenditure,” according to the Pennington article. “But the new research supports the idea that it’s more than age-related changes in lifestyle or body composition.” 

Until more research comes, we can rest in the fact that our bodies are amazing, unique machines no matter what stage of metabolism we are in. 

STAGE 1 – INFANCY TO ONE YEAR: Highest metabolism
STAGE 2 – ONE YEAR TO 20s: Metabolism slows by 3% per year
STAGE 3 – 20s TO 50s: Metabolism stays the same
STAGE 4 – 60s AND BEYOND: Metabolism declines by 0.7% each year


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