Using data collected over 40 years from half a dozen labs and 6,500 test subjects ages 8 days to 95 years, researchers (80 of them!) have upended some conventional assumptions about metabolism, most notably that our metabolisms slow down around middle age and that women have slower metabolisms than men. It turns out that neither is true. (Metabolism, by the way, is the sum of all chemical reactions in our bodies, but more easily understood as the breakdown of food and its transformation into energy—aka calorie burning.) As one scientist remarked: “We will have to revise some of our ideas. It will be in textbooks.”
Specifically, the researchers learned that metabolism differs for all people across four distinct stages of life:
- Infancy up until age 1: Calorie burning is at its peak, accelerating until it is 50 percent above the adult rate.
- Ages 1 to 20: Metabolism gradually slows by about 3 percent a year.
- Ages 20 to 60: Metabolism holds steady.
- After age 60: metabolism declines by about 0.7 percent a year.
As you can see, your metabolism rate depends on your age, and
the slowdown doesn’t start at 40. Thus, if you started gaining weight after 40,
you can’t blame it on metabolism. You’ll have to wait until you’re over 60 to
do that. As you can see also, if you just graduated from college, you’re
burning fewer calories than you did when you were a freshman.
While the above results were true for the general population,
a few people had metabolic rates 25 percent below the average for their age and
others have rates 25 percent higher than expected. These outliers will open a
number of research questions, such as understanding the characteristics of such
people and whether there is a relationship with obesity.
I started gaining weight in my 50s, as do many women in
that age bracket. I blamed it on menopause (I still do). But I can’t blame it
on a slower metabolism.
For an introduction to this blog, see I Just Say No; for a list of blog topics, click the Topics tab.
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