Metabolism

Groundbreaking Study

The New York Times reported a new study in Science that has everyone talking about metabolism. Using data from thousands, ranging in age from 8 days to 95 years, researchers discovered four distinct periods of life, as far as metabolism goes. They also found that there are no real differences between the metabolic rates of men and women.

The conventional wisdom about metabolism is a myth. Metabolisms does not slow down as we age. Women do not have slower metabolisms than men. The new study’s principal investigator, Herman Pontzer, an evolutionary anthropologist at Duke University, said:

“It was really clear that we didn’t have a good handle on how body size affects metabolism or how aging affects metabolism. These are basic fundamental things you’d think would have been answered 100 years ago.”

Four Life Stages

Central to their findings was that metabolism differs for all people across four distinct stages of life.

1. There’s infancy, up until age 1, when calorie burning is at its peak, accelerating until it is 50 percent above the adult rate.
2. Then, from age 1 to about age 20, metabolism gradually slows by about 3 percent a year.
3. From age 20 to 60, it holds steady.
4. And, after age 60, it declines by about 0.7 percent a year. The metabolic slowing that starts around age 60 results in a 20 percent decline in the metabolic rate by age 95.

The four periods of metabolic life depicted in the new paper show “there isn’t a constant rate of energy expenditure per pound,” Dr. Redman noted. The rate depends on age. That runs counter to the longstanding assumptions she and others in nutrition science held.

A slower metabolism after age 60 may mean that crucial organs are functioning less well as people age. It might be one reason that chronic diseases tend to occur most often in older people.