中年发福不是新陈代谢的锅！研究发现60岁后新陈代谢才开始变慢
Metabolism peaks at age one and tanks after 60, study finds

Middle-aged spread cannot be blamed on a waning metabolism, according to an unprecedented analysis of the body's energy use.

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.

The study, published in the journal Science, found four phases of metabolic life:

1. 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

2. a gentle slowdown until the age of 20, with no spike during all the changes of puberty

3. no change at all between the ages of 20 and 60

4. a permanent decline, with yearly falls that, by 90, leave metabolism 26% lower than in mid-life

"It is a picture we've never really seen before and there is a lot of surprises in it," one of the researchers, Prof John Speakman, from the University of Aberdeen, said.

"The most surprising thing for me is there is no change throughout adulthood - if you are experiencing mid-life spread you can no longer blame it on a declining metabolic rate."

People's metabolism was measured using doubly labelled water.

Made from heavier forms of the hydrogen and oxygen atoms that make up water, this can be tracked as it leaves the body.

But doubly labelled water is incredibly expensive, so it took researchers working together across 29 countries to gather data on 6,400 people.

The researchers said fully understanding the shifting metabolism could have implications in medicine.

Prof Herman Pontzer from Duke University said it could help reveal whether cancers spread differently as the metabolism changes and if drug doses could be adjusted during different phases.

And there is even discussion about whether drugs that modify the metabolism could slow diseases of old age.

Drs Rozalyn Anderson and Timothy Rhoads, from the University of Wisconsin, said the "unprecedented" study had already led to "important new insights into human metabolism".

And it "cannot be a coincidence" diseases of old age kicked in as the metabolism fell.

Prof Tom Sanders, from King's College London, said: "Interestingly, they found very little differences in total energy expenditure between early adult life and middle age - a time when most adults in developed countries put on weight.

"These findings would support the view that the obesity epidemic is fuelled by excess food energy intake and not a decline in energy expenditure."