Life Stages

Environmental & Science Education, STEM, Health, Medicine

Ed Hessler

In Garrison Keillor's Post to the Host Comments (week of 08.08.21), a reader reported being told by his doctor when he greeted his doctor with "You're looking good." The doctor respnded, “There’s four stages of life: youth, middle age, old age, and you’re looking good.”

The following week (08.15.21) a reader noted that this was "A good line but … in 1960, a neighbor told me there were five stages: youth, middle age, old age, dotage, and anecdotage."

Scientists have added another way of thinking about human stages of life, one based on our metabolism. The research was reported in the journal Science (13 August 2021) by Duke University evolutionary anthropologist Herman Pontzer et. al.  (There are more than 80 co-authors.) The stages are:

Stage One: Infancy to ~ age1. During this stage we burn calories at a tremendous rate, i.e., "pound-for-pound, a one-year-old burns calories 50% faster than an adult."

Stage Two: Age 1 to ~ age 20. Metabolism slows some 3% a year.

Stage Three. Age 20 to ~  age 60, metabolism is steady.

Stage Four. After age 60. Perhaps I should add that, for some, this is the "dreaded" stage four when metabolism declines by 0.7% a year." During this period it is easier to add pounds than shed them.

The findings were the same for men and women. Obviously, individuals vary. It is a story of cells slowing down as we age.

There is a story about the findings by Robin A. Smith in Duke Research with a link to the paper in Science (behind a pay wall). Smith writes “There are lots of physiological changes that come with growing up and getting older,” said study co-author Herman Pontzer, associate professor of evolutionary anthropology at Duke University. “Think puberty, menopause, other phases of life. What's weird is that the timing of our ‘metabolic life stages’ doesn't seem to match those typical milestones.”

"Pontzer and an international team of scientists analyzed the average calories burned by more than 6,600 people ranging from one week old to age 95 as they went about their daily lives in 29 countries worldwide."

The Duke Research link to the original study will only allow you to read the abstract and to learn more about the authors and their affiliations, unless you are a member of the American Association for the Advancement of Science (AAAS).

Pontzer is the author of a popular book, Burn, on how we burn calories, lose weight and stay healthy. Smith wrote a story about this book for Duke Research which includes and interview with Pontzer and on his research counting calories with the Hadza in Tanzania.