What We Think We Know About Metabolism May Be Wrong
20岁以后新陈代谢放缓？新研究颠覆传统观点

Everyone knows conventional wisdom about metabolism: People put pounds on year after year from their 20s onward because their metabolisms slow down, especially around middle age. Women have slower metabolisms than men. That’s why they have a harder time controlling their weight. Menopause only makes things worse, slowing women’s metabolisms even more.

所有人都知道关于新陈代谢的传统观点：从20多岁开始，人的体重年复一年地增加，因为他们的新陈代谢速度放缓，尤其是在中年前后。女性的新陈代谢比男性慢。所以她们更加难控制体重。更年期只会让事情变得更糟，使女性的新陈代谢更加缓慢。

All wrong, according to a paper published Thursday in Science. Using data from nearly 6,500 people, ranging in age from 8 days to 95 years, researchers discovered that there are 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 after controlling for other factors.

The findings from the research are likely to reshape the science of human physiology and could also have implications for some medical practices, like determining appropriate drug doses for children and older people.

这项研究的发现可能会重塑人类生理学，也可能对一些医疗实践产生影响，比如为儿童和老年人确定合适的药物剂量。

“It will be in textbooks,” predicted Leanne Redman, an energy balance physiologist at Pennington Biomedical Research Institute in Baton Rouge, La., who also called it “a pivotal paper.”

路易斯安那州巴吞鲁日的彭宁顿生物医学研究所(Pennington Biomedical Research Institute)的能量平衡生理学家利安·雷德曼(Leanne Redman)预测说：“它将出现在教科书中。”他还称这是一篇“关键性论文”。

Rozalyn Anderson, a professor of medicine at the University of Wisconsin, Madison, who studies aging, wrote a perspective accompanying the paper. In an interview, she said she was “blown away” by its findings. “We will have to revise some of our ideas,” she added.

威斯康星大学麦迪逊分校(University of Wisconsin, Madison)研究老龄化问题的医学教授罗泽林·安德森(Rozalyn Anderson)写了与论文配套的观点文章。在采访中，她说她被调查结果“震惊”了。“我们将不得不修正一些想法，”她还说。

But the findings’ implications for public health, diet and nutrition are limited for the moment because the study gives “a 30,000-foot view of energy metabolism,” said Dr. Samuel Klein, who was not involved in the study and is director of the Center for Human Nutrition at the Washington University School of Medicine in St. Louis. He added, “I don’t think you can make any new clinical statements” for an individual. When it comes to weight gain, he says, the issue is the same as it has always been: People are eating more calories than they are burning.

但在目前，这些发现对公共卫生、饮食和营养的影响是有限的，因为研究给出的是“关于能量代谢的宏观视角，”圣路易斯的华盛顿大学医学院人类营养中心(Center for Human Nutrition at the Washington University School of Medicine)的主任塞缪尔·克莱因(Samuel Klein)博士说，他并没有参与这项研究。他还说，就个人层面而言，“我不认为你可以就此做出什么新的临床陈述。”当涉及体重增加时，他说，问题一如既往：人们摄入的卡路里比燃烧的卡路里要多。

Metabolic research is expensive, and so most published studies have had very few participants. But the new study’s principal investigator, Herman Pontzer, an evolutionary anthropologist at Duke University, said that the project’s participating researchers agreed to share their data. There are more than 80 co-authors on the study. By combining efforts from a half dozen labs collected over 40 years, they had sufficient information to ask general questions about changes in metabolism over a lifetime.

代谢研究是昂贵的，所以大多数发表的研究只有很少的参与者。但是这项新研究的首席研究员、杜克大学(Duke University)进化人类学家赫尔曼·庞泽(Herman Pontzer)说，参与该项目的研究人员同意分享他们的数据。这项研究有80多位合著者。通过结合40多年来收集的六个实验室的努力，他们有足够的信息来探寻一生中新陈代谢变化的一般问题。

All of the research centers involved in the project were studying metabolic rates with a method considered the gold standard — doubly labeled water. It involves measuring calories burned by tracking the amount of carbon dioxide a person exhales during daily activities.

所有参与该项目的研究中心都在用一种被认为是黄金标准的方法研究新陈代谢率——双标水法。它包括通过跟踪一个人在日常活动中呼出的二氧化碳量来测量燃烧的卡路里。

The investigators also had participants’ heights and weights and percent body fat, which allowed them to look at fundamental metabolic rates. A smaller person will burn fewer calories than a bigger person, of course, but correcting for size and percent fat, the group asked, Were their metabolisms different?

研究人员还掌握了参与者的身高、体重和体脂率，从而了解基本代谢率。当然，身材矮小的人燃烧的卡路里要比身材高大的人少，但是研究小组问道，如果根据体型和体脂做出修正后，他们的新陈代谢是否不同？

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

“很明显，我们并没有很好地掌握体型如何影响新陈代谢，或者衰老如何影响新陈代谢，”庞泽说。“这些都是基本的基础问题，你会认为100年前就已经有了答案。”

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

他们研究结果的核心是，在生命的四个不同阶段，所有人的新陈代谢都有所不同。

• There’s infancy, up until age 1, when calorie burning is at its peak, accelerating until it is 50 percent above the adult rate.

· 从婴儿期到一岁，这段时间的卡路里燃烧达到顶峰，并加速上升，直到比成人的燃烧速度高出50%。

• Then, from age 1 to about age 20, metabolism gradually slows by about 3 percent a year.

· 然后，从一岁到20岁左右，新陈代谢每年放缓约3%。

• From age 20 to 60, it holds steady.

· 从20岁到60岁，这个比例保持稳定。

• And, after age 60, it declines by about 0.7 percent a year.

· 60岁以后，每年下降约0.7%。

Once the researchers controlled for body size and the amount of muscle people have, they also found no differences between men and women.

一旦研究人员控制了体型和肌肉数量，他们还发现男女之间没有差异。

As might be expected, while the metabolic rate patterns hold for the population, individuals vary. Some have metabolic rates 25 percent below the average for their age and others have rates 25 percent higher than expected. But these outliers do not change the general pattern, reflected in graphs showing trajectory of metabolic rates over the years.

正如预期的那样，虽然代谢率模式对群体来说是不变的，但个体是不同的。一些人的代谢率比同龄者的平均水平低25%，而另一些人的代谢率比预期的高25%。但这些异常值并没有改变总体模式，这反映在多年来的代谢率轨迹图表上。

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.

雷德曼指出，在这篇新论文中描述的代谢生命的四个阶段表明“每磅的能量消耗率并不恒定”。这个比率取决于年龄。这与她和其他营养学专家长期以来持有的假设背道而驰。

The trajectories of metabolism over the course of a lifetime and the individuals who are outliers will open a number of research questions. For instance, what are the characteristics of people whose metabolisms are higher or lower than expected, and is there a relationship with obesity?

一生中新陈代谢的轨迹以及异常者的数据将会开启许多研究问题。例如，新陈代谢高于或低于预期的人有什么特征，与肥胖有什么关系？

One of the findings that most surprised Dr. Pontzer was the metabolism of infants. He expected, for example, that a newborn infant would have a sky-high metabolic rate. After all, a general rule in biology is that smaller animals burn calories faster than larger ones.

最令庞泽吃惊的发现之一是婴儿的新陈代谢。例如，他预计新生儿的代谢率会极高。毕竟，生物学的一般规律是，小动物燃烧卡路里的速度比大动物快。

Instead, Dr. Pontzer said, for the first month of life, babies have the same metabolic rate as their mothers. But shortly after a baby is born, he said, “something kicks in and the metabolic rate takes off.”

相反，庞泽说，在婴儿出生的第一个月里，他们的新陈代谢率和母亲是一样的。但在婴儿出生后不久，他说，“一些东西开始发挥作用，代谢率开始上升。”

The group also expected the metabolism of adults to start slowing when they were in their 40s or, for women, with the onset of menopause.

同样，研究小组本以为会发现，成年人的新陈代谢在40多岁时开始放缓，对女性来说，是随着更年期开始。

But, Dr. Pontzer said, “we just didn’t see that.”

但是，庞泽说，“我们没有看到这一点。”

The metabolic slowing that starts around age 60 results in a 20 percent decline in the metabolic rate by age 95.

60岁左右开始的代谢减缓会导致到95岁时代谢率下降20%。

Dr. Klein said that although people gain on average more than a pound and a half a year during adulthood, they can no longer attribute it to slowing metabolisms.

克莱因说，尽管成年期平均每年增重1.5磅以上，但他们不能再将其归咎于新陈代谢放缓。

Energy requirements of the heart, liver, kidney and brain account for 65 percent of the resting metabolic rate although they constitute only 5 percent of body weight, Dr. Klein said. A slower metabolism after age 60, he added, 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.

克莱因说，心脏、肝脏、肾脏和大脑的能量需求占静息代谢率的65%，尽管它们只占体重的5%。他还说，60岁以后新陈代谢变慢可能意味着，随着年龄的增长，关键器官的功能会下降。这可能是慢性病最常发生在老年人身上的原因之一。

Even college students might see the effects of the metabolic shift around age 20, Dr. Klein said. “When they finish college they are burning fewer calories than when they started.”

他说，即使是大学生也可能在20岁左右就能看到代谢变化的影响。“当他们完成大学学业时，他们消耗的卡路里比入学时要少。”

And around age 60, no matter how young people look, they are changing in a fundamental way.

在60岁左右，无论人们看起来多么年轻，他们都在发生根本性的变化。

“There is a myth of retaining youth,” Dr. Anderson said. “That’s not what the biology says. In and around age 60, things start to change.”

“有一个留住青春的神话，”安德森说。“但生物学不是这么说的。到了60岁左右，情况开始发生变化。”

“There is a time point when things are no longer as they used to be.”