It is commonly accepted dogma that our metabolism slows as we age, and that this is a contributing factor to weight gain as we get older.  A recent study has caused quite a stir, because it goes against what we have previously understood about metabolism, suggesting that it actually doesn’t change through most of adult life.


So which is it?? Does metabolism decline in our adult years, or not?


The study was nicely summarized by my colleague Dr Arya Sharma, so I won’t review it in detail here. Essentially, this comprehensive analysis of the existing database of energy expenditure studies found that there are four distinct life phases of energy expenditure.  One of these phases is from age 20-60 years, where they found that total and resting energy expenditure is stable.  They found that energy burn starts to decline only after age 60.


Here’s the catch:  What this study actually found is that fat-free mass adjusted energy expenditure remains stable from age 20-60.  In other words, when they established that metabolism stays stable from age 20-60, this is with the assumption that lean mass (much of which is muscle) stays the same from age 20-60.  As adults, most of us lose lean (muscle) mass during our adult years, so metabolism actually does decrease for most of us over these years.
BOTTOM LINE:  In adulthood, metabolism DOES decrease over time for most of us, in concert with a gradual decrease in lean (muscle) mass.
PS Check out my colleague Dr Kushner’s blog on the topic (also one of the study’s coauthors) here.

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