Metabolism, the the chemical processes that occur within a living organism in order to maintain life, peaks at age one and tanks after 60, a study has found.
The study, published in the journal Science, said that middle-aged spread cannot be blamed on a waning metabolism, reports the BBC.
The study, of 6,400 people, from eight days old up to age 95, in 29 countries, suggests the metabolism remains "rock solid" throughout mid-life.
It peaks at the age of one, is stable from 20 to 60 and then inexorably declines.
Researchers said the findings gave surprising new insights about the body.
The metabolism is every drop of chemistry needed to keep the body going.
And the bigger the body - whether that is ripped muscles or too much belly fat - the more energy it will take to run.
The study has found four phases of metabolic life:
- birth to age one, when the metabolism shifts from being the same as the mother's to a lifetime high 50% above that of adults
- a gentle slowdown until the age of 20, with no spike during all the changes of puberty
- no change at all between the ages of 20 and 60
- a permanent decline, with yearly falls that, by 90, leave metabolism 26% lower than in mid-life