體育運動本身并不會讓你變瘦

Two groundbreaking new studies address the irksome question of why so many of us who work out remain so heavy, a concern that carries special resonance at the moment, as lean Olympians slip through the air and water, inspiring countless viewers to want to become similarly sleek.

為什么我們之中的許多人光鍛煉可就是不見瘦?兩項突破性的新研究把目標(biāo)對準(zhǔn)了這個令人煩惱的問題。在這個夏天，目睹奧運健兒瘦削如刀的身影滑過空氣與水面，無數(shù)觀眾想必正大受鼓舞，心向往之。對于他們，這個問題想必會引起特別的共鳴。

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.

在一個有付出就有回報的世界中，經(jīng)常從事體育運動照理說應(yīng)該是會讓人變瘦的。但不斷有研究顯示，許多人開始健身后只減掉了一丁點兒體重，或者絲毫沒變。有些人甚至還更重了。

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.

為了更好的理解其中緣由，人類學(xué)家展開了一系列新研究，其中一項更遠(yuǎn)赴非洲的坦桑尼亞。在那里，研究人員從仍在過著狩獵采集生活的哈德薩(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.

研究者們應(yīng)用現(xiàn)代田徑運動研究技術(shù)對這些部落成員來了場突擊特訓(xùn)。安裝在實驗對象身上的全球衛(wèi)星定位(GPS)裝置毫厘不爽地測量記錄下他們每日覓食過程中走過的距離。他們按要求服下“雙標(biāo)水”——一種以同位素示蹤物替換掉普通氫和氧分子的液體。通過研究尿液中的這些成分，研究者可以準(zhǔn)確地測定一個人的能量消耗和新陳代謝率。

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.

研究人員收集了11天的數(shù)據(jù)，由此計算出參加實驗者的日?；顒幽Ｊ?、能量消耗及靜息代謝率(resting metabolic rates)。這些數(shù)據(jù)隨即與普通西方男性和女性的相應(yīng)指標(biāo)加以對比。

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.

長久以來，人們一直認(rèn)為，過著狩獵-采集式生活的人體力活動強(qiáng)度相當(dāng)之高，因此也就會比那些天天坐辦公室的普通美國人燃燒更多的卡路里。這倒也沒錯?？茖W(xué)家們已確定，哈德薩人總體上的確比眾多美國人運動更多，男性部落成員每天步行約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.

但他們并沒有燃燒更多的卡路里。事實上，科學(xué)家們計算得出，哈德薩人的平均新陳代謝率——換言之，他們在一天中所消耗的卡路里——與西方人的平均新陳代謝率幾乎沒什么差別。

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.

科學(xué)家由此得出結(jié)論，“如果膳食結(jié)構(gòu)改變，能量攝入增加，勤于運動的'傳統(tǒng)'生活方式并不能讓人免于發(fā)胖”。這也就是說，即便是好動的人，如果像大多數(shù)西方人那樣大吃大喝，也會體重漸增。

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.)

這項研究所傳達(dá)的隱含且令人泄氣的信息當(dāng)然便是，體育運動本身并不會讓你變瘦并保持苗條。(值得注意的是，哈德薩人幾乎無一例外的又瘦又小。)

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.

路易斯安那州彭寧頓生物醫(yī)學(xué)研究中心(Pennington Biomedical Research Center)的蒂莫西·丘奇(Dr. Timothy Church)指出，發(fā)表于《公共圖書館·綜合》(PLoS One)雜志上的該項研究，其關(guān)鍵性的結(jié)論既不新奇也不出人意外。丘奇醫(yī)生是該研究中心的約翰·S·麥基爾亨利講座教授(John S. McIlhenny Endowed Chair)，長期從事運動與體重控制領(lǐng)域的研究。“以等量卡路里換算，通過節(jié)食減輕體重要比借助鍛煉容易，對此我們已經(jīng)知道了頗有一段時間，”丘奇說。

People stick with low-calorie diets more readily than they continue with exercise to drop pounds.

對于同一人群，堅持低熱量膳食也比持續(xù)鍛煉體重減輕得更快。

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，丘奇醫(yī)生與他人合作，發(fā)表了一篇有趣的研究綜述，旨在解釋個中奧秘。文章的主要觀點是，正如“哈德薩”研究所揭示的，人類的新陳代謝并不像此前認(rèn)為的那樣可以很容易地通過運動加以提升。

"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.

“有人指望說，一旦鍛煉了，新陳代謝率就不會隨著體重降低而變緩，甚至還會加速，”負(fù)責(zé)此項研究的新澤西州蒙特克萊爾州立大學(xué)數(shù)學(xué)教授戴安娜·托馬斯(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，對以往健身與減重的相關(guān)研究加以精確數(shù)學(xué)分析后顯示，那種樂觀的預(yù)期事實上查無實據(jù)。在少數(shù)對鍛煉、食物攝入和新陳代謝率加以嚴(yán)格監(jiān)測的研究中，一項研究甚至發(fā)現(xiàn)，志愿者的基礎(chǔ)代謝率隨著體重降低而變緩，即便他們?nèi)詧猿置咳者\動。結(jié)果是，雖然這些人在健身過程中燃燒了500卡路里熱量，他們每天消耗的熱量卻比新陳代謝率保持不變時要少，而減輕的體重也不如預(yù)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.

對于想要通過鍛煉擺脫身上贅肉的我們來說，問題在于，當(dāng)下通用的大多數(shù)鍛煉與減重計算公式假設(shè)新陳代謝率是一成不變的，或者可以通過運動加以提升。

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，托馬斯教授將新陳代謝率減緩的因素考慮在內(nèi)，重新計算出了一套減重公式。在彭寧頓醫(yī)學(xué)中心，托馬斯與一群的志愿者合作，使用新的公式幫助他們更好的推算出通過健身而有望減少的體重值。

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."

托馬斯指出，經(jīng)驗證，這些推算結(jié)果十分準(zhǔn)確，盡管她的推算公式不像老公式那樣承諾大幅度減輕體重，但志愿者們卻很開心。“降低期待值，實現(xiàn)目標(biāo)，這要比好高騖遠(yuǎn)然后以失望告終而好得多。”

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。過去幾年里，托馬斯已經(jīng)成功減掉了70磅體重。靠著每天步行，以及用自己發(fā)明的公式計算出每日實際消耗的卡路里，她的體重一點兒都沒反彈。