体育运动本身并不会让你变瘦
为什么我们之中的许多人光锻炼可就是不见瘦?两项突破性的新研究把目标对准了这个令人烦恼的问题。在这个夏天，目睹奥运健儿瘦削如刀的身影滑过空气与水面，无数观众想必正大受鼓舞，心向往之。对于他们，这个问题想必会引起特别的共鸣。
And in a just world, frequent physical activity should make us slim. But repeated studies have shown that many people who begin an exercise program lose little or no weight. Some gain.
在一个有付出就有回报的世界中，经常从事体育运动照理说应该是会让人变瘦的。但不断有研究显示，许多人开始健身后只减掉了一丁点儿体重，或者丝毫没变。有些人甚至还更重了。
To better understand why, anthropologists leading one of the new studies began with a research trip to Tanzania. There, they recruited volunteers from the Hadza tribe, whose members still live by hunting and gathering.
为了更好的理解其中缘由，人类学家展开了一系列新研究，其中一项更远赴非洲的坦桑尼亚。在那里，研究人员从仍在过着狩猎采集生活的哈德萨(Hadza)部落中招募了一批志愿者。
Providing these tribespeople with a crash course in modern field-study technology, the researchers fitted them with GPS units, to scrupulously measure how many miles each walked daily while searching for food. They also asked them to swallow so-called doubly labeled water, a liquid in which the normal hydrogen and oxygen molecules have been replaced with versions containing tracers. By studying these elements later in a person's urine, researchers can precisely determine someone's energy expenditure and metabolic rate.
研究者们应用现代田径运动研究技术对这些部落成员来了场突击特训。安装在实验对象身上的全球卫星定位(GPS)装置毫厘不爽地测量记录下他们每日觅食过程中走过的距离。他们按要求服下“双标水”——一种以同位素示踪物替换掉普通氢和氧分子的液体。通过研究尿液中的这些成分，研究者可以准确地测定一个人的能量消耗和新陈代谢率。
The researchers gathered data for 11 days, then calculated the participants' typical daily physical activity, energy expenditure and resting metabolic rates. They then compared those numbers with the same measures for an average male and female Westerner.
研究人员收集了11天的数据，由此计算出参加实验者的日常活动模式、能量消耗及静息代谢率(resting metabolic rates)。这些数据随即与普通西方男性和女性的相应指标加以对比。
It's long been believed that a hunter-gatherer lifestyle involves considerable physical activity and therefore burns many calories, far more than are incinerated by your average American office worker each day. And it was true, the scientists determined, that the Hadza people in general moved more than many Americans do, with the men walking about seven miles a day and the women about three.
长久以来，人们一直认为，过着狩猎-采集式生活的人体力活动强度相当之高，因此也就会比那些天天坐办公室的普通美国人燃烧更多的卡路里。这倒也没错。科学家们已确定，哈德萨人总体上的确比众多美国人运动更多，男性部落成员每天步行约7英里，女性也在3英里左右。
But it was not true that they were burning far more calories. In fact, the scientists calculated, the Hadza's average metabolic rate, or the number of calories that they were burning over the course of a day, was about the same as the average metabolic rate for Westerners.
但他们并没有燃烧更多的卡路里。事实上，科学家们计算得出，哈德萨人的平均新陈代谢率——换言之，他们在一天中所消耗的卡路里——与西方人的平均新陈代谢率几乎没什么差别。
The implication, the scientists concluded, is that "active, 'traditional' lifestyles may not protect against obesity if diets change to promote increased caloric consumption." That is, even active people will pack on pounds if they eat like most of us in the West.
科学家由此得出结论，“如果膳食结构改变，能量摄入增加，勤于运动的'传统'生活方式并不能让人免于发胖”。这也就是说，即便是好动的人，如果像大多数西方人那样大吃大喝，也会体重渐增。
The underlying and rather disheartening message of that finding, of course, is that physical activity by itself is not going to make and keep you thin. (It's worth noting that the Hadza people were almost uniformly slight.)
这项研究所传达的隐含且令人泄气的信息当然便是，体育运动本身并不会让你变瘦并保持苗条。(值得注意的是，哈德萨人几乎无一例外的又瘦又小。)
The overarching conclusion of that study, which was published last week in the journal PLoS One, is not really new or surprising, says Dr. Timothy Church, who holds the John S. McIlhenny Endowed Chair in Health Wisdom at the Pennington Biomedical Research Center in Louisiana and who has long studied exercise and weight control. "It's been known for some time that, calorie for calorie, it's easier to lose weight by dieting than by exercise," he says.
路易斯安那州彭宁顿生物医学研究中心(Pennington Biomedical Research Center)的蒂莫西·丘奇(Dr. Timothy Church)指出，发表于《公共图书馆·综合》(PLoS One)杂志上的该项研究，其关键性的结论既不新奇也不出人意外。丘奇医生是该研究中心的约翰·S·麦基尔亨利讲座教授(John S. McIlhenny Endowed Chair)，长期从事运动与体重控制领域的研究。“以等量卡路里换算，通过节食减轻体重要比借助锻炼容易，对此我们已经知道了颇有一段时间，”丘奇说。
People stick with low-calorie diets more readily than they continue with exercise to drop pounds.
对于同一人群，坚持低热量膳食也比持续锻炼体重减轻得更快。
And another newly published and fascinating review, by Dr. Church and others, goes some way to explaining why. Its main point: As in the Hadza study, human metabolism appears to be less revved by activity than was once believed.
最近，丘奇医生与他人合作，发表了一篇有趣的研究综述，旨在解释个中奥秘。文章的主要观点是，正如“哈德萨”研究所揭示的，人类的新陈代谢并不像此前认为的那样可以很容易地通过运动加以提升。
"There's this expectation that if you exercise, your metabolism won't drop as you lose weight or will even speed up," says Diana Thomas, a professor of mathematics at Montclair State University in New Jersey, who led the study.
“有人指望说，一旦锻炼了，新陈代谢率就不会随着体重降低而变缓，甚至还会加速，”负责此项研究的新泽西州蒙特克莱尔州立大学数学教授戴安娜·托马斯(Diana Thomas)指出。
But she says close mathematical scrutiny of past studies of exercise and weight loss shows that that happy prospect is, sad to say, unfounded. One of the few studies ever to have scrupulously monitored exercise, food intake and metabolic rates found that volunteers' basal metabolic rates dropped as they lost weight, even though they exercised every day. As a result, although they were burning up to 500 calories during an exercise session, their total daily caloric burn was lower than it would have been had their metabolism remained unchanged, and they lost less weight than had been expected.
但她表示，对以往健身与减重的相关研究加以精确数学分析后显示，那种乐观的预期事实上查无实据。在少数对锻炼、食物摄入和新陈代谢率加以严格监测的研究中，一项研究甚至发现，志愿者的基础代谢率随着体重降低而变缓，即便他们仍坚持每日运动。结果是，虽然这些人在健身过程中燃烧了500卡路里热量，他们每天消耗的热量却比新陈代谢率保持不变时要少，而减轻的体重也不如预想中的多。
The problem for those of us hoping to use exercise to slough off fat is that most current calculations about exercise and weight loss assume that metabolism remains unchanged or is revved by exercise.
对于想要通过锻炼摆脱身上赘肉的我们来说，问题在于，当下通用的大多数锻炼与减重计算公式假设新陈代谢率是一成不变的，或者可以通过运动加以提升。
So Dr. Thomas has helpfully begun to recalibrate weight loss formulas, taking into account the drop in metabolism. Using her new formulas, she's working with a group of volunteers at Pennington, providing them with improved predictions about how much weight they can expect to lose from exercise.
鼓舞人心的消息是，托马斯教授将新陈代谢率减缓的因素考虑在内，重新计算出了一套减重公式。在彭宁顿医学中心，托马斯与一群的志愿者合作，使用新的公式帮助他们更好的推算出通过健身而有望减少的体重值。
The predictions are proving accurate, she says, and although her forecast is for less weight loss than that under the old formula, the volunteers are pleased. "It's better to meet lower expectations," she says, "than to be disappointed that you're not losing what you supposedly should."
托马斯指出，经验证，这些推算结果十分准确，尽管她的推算公式不像老公式那样承诺大幅度减轻体重，但志愿者们却很开心。“降低期待值，实现目标，这要比好高骛远然后以失望告终而好得多。”
She is perhaps her own best advertisement. In the past few years, she's shed 70 pounds and, using her formulas for how many calories she's actually burning each day thanks to a daily walk, has regained none of it.
她是自己的活招牌。过去几年里，托马斯已经成功减掉了70磅体重。靠着每天步行，以及用自己发明的公式计算出每日实际消耗的卡路里，她的体重一点儿都没反弹。
