Thermogenesis, the food processing part of your metabolism, actually stays fairly steady throughout your adult life. The illusion that your metabolism slows as you age actually occurs because as you get older, your muscle mass decreases and your amount of fat tends to increase, decreasing your BMR and the amount of calories your body burns. This in turn decreases the amount of calories you need to take in through your diet.
Your activity levels can significantly affect the speed of your metabolism.
In fact, activity — both exercise and non-exercise activity — makes up roughly 10–30% of your calories burned daily. For very active people, this number can be as high as 50% (4).
Non-exercise activity thermogenesis (NEAT) is the calories burned through activity other than exercise. This includes tasks like standing, washing the dishes and other household chores.
Unfortunately, older adults are typically less active and burn fewer calories through activity.
Research shows that over a quarter of Americans aged 50–65 don’t exercise outside of work. For people over 75, this increases to over a third (5).
Research also shows that older adults burn roughly 29% fewer calories through NEAT (6).
Staying active can help prevent this drop in metabolism.
One study of 65 healthy young people (21–35 years) and older people (50–72 years) showed that regular endurance exercise prevents metabolism from slowing down with age (7).
As people age, their metabolism slows down.
Starting in your 20s, your metabolism begins to slow down.In your 30s, your metabolism rate slows even more.
Metabolism slows about 5 percent every 10 years after age 40, according to the U.S. Department of Health and Human ServicesOff Site Icon (HHS).
Talk to your doctor for more information about changes in metabolism as you age.