過(guò)去幾十年所有的減肥建議可以總結(jié)為一句話：卡路里消耗大于攝入。這種說(shuō)法基于卡路里消耗守則，即消耗3500卡路里等于減輕一磅體重。簡(jiǎn)潔直觀，讓人感覺(jué)減肥并不難。

但這個(gè)原則也讓無(wú)數(shù)節(jié)食者非常沮喪，因?yàn)橹境瑯?biāo)仿佛等于缺乏意志力。按理說(shuō)，占美國(guó)總?cè)丝?9%的體重超標(biāo)人士只要少吃多運(yùn)動(dòng)，就不會(huì)到處出現(xiàn)肥胖問(wèn)題。盡管多年來(lái)不少科研人員質(zhì)疑3500卡路里法則，但早已形成人們對(duì)體重和新陳代謝的共識(shí)。

不過(guò)，情況開(kāi)始變化。諷刺的是，這種新轉(zhuǎn)變的主要推手竟然是一檔減肥真人秀節(jié)目——美國(guó)全國(guó)廣播公司（NBC）的《超級(jí)減肥王》（Biggest Loser）。（要求選手在30周內(nèi)比賽減肥，減重百分比最高者獲勝。）正是這檔節(jié)目第一次告訴人們減肥與意志力關(guān)系沒(méi)那么緊密。

而新近研究顯示，真相可能更加復(fù)雜。去年5月發(fā)布的一項(xiàng)研究稱，研究人士追蹤了14位第八季《超級(jí)減肥王》參賽者，記錄了加入該節(jié)目前的體重、新陳代謝水平，健身計(jì)劃和食譜，在節(jié)目錄制期間不同時(shí)點(diǎn)和第八季結(jié)束六年后記錄各項(xiàng)水平。

不出所料，所有14名參賽前明顯超重，錄制節(jié)目期間都大幅減重。令人意外的是，除了一位選手，其他13位在研究將近尾聲時(shí)體重都有所反彈，其中4位選手的體重已超過(guò)參賽前。

真正讓人大跌眼鏡的是，研究人員發(fā)現(xiàn)減肥期間和成功減重后，參賽者的身體總在努力恢復(fù)原有體重：參賽減重后，選手的新陳代謝水平整體劇減，意思是他們消耗的卡路里低于相同體形常規(guī)消耗水平。而且不是短期現(xiàn)象，幾年后多數(shù)選手的新陳代謝水平非但沒(méi)能回升，還繼續(xù)下滑。到研究結(jié)束時(shí)，減重239磅奪得第八季冠軍的丹尼?卡希爾六年內(nèi)反彈100磅，日均基礎(chǔ)熱量消耗較同體形人士常規(guī)水平少800卡路里。

該研究第一作者凱文?霍爾認(rèn)為，研究結(jié)果明確顯示不應(yīng)把減肥視為只靠意識(shí)力就能解決的問(wèn)題。他解釋說(shuō)：“可以減少攝入卡路里，增加活動(dòng)，但身體會(huì)抗拒改變。” 不妨把人體想象成一根弦。如果你不減肥，弦是松弛的。一旦減少攝入卡路里多運(yùn)動(dòng)，弦就繃得越來(lái)越緊。瘦身食譜和鍛煉越猛，弦就拉得越緊，身體恢復(fù)原有體重的反彈力就越大。

“你減肥多努力，阻力就多大。”霍爾說(shuō)。如果你想保住減肥成果，就得永遠(yuǎn)跟阻力作斗爭(zhēng)。有點(diǎn)像《第22條軍規(guī)》。減肥越成功，你的身體就越努力恢復(fù)原來(lái)的體重。事實(shí)上，《超級(jí)減肥王》節(jié)目里減肥最成功的選手賽后新陳代謝水平下降最快。

聽(tīng)起來(lái)有點(diǎn)讓人絕望，某種程度上的確如此。研究認(rèn)為，減肥絕非簡(jiǎn)單地少吃多運(yùn)動(dòng)。但霍爾覺(jué)得，《超級(jí)減肥王》比賽的后續(xù)報(bào)道把重點(diǎn)放在參賽者復(fù)胖，其實(shí)夸大了負(fù)面影響。他注意到，《紐約時(shí)報(bào)》等多家媒體高調(diào)報(bào)道后，出現(xiàn)令人失望的傾向：讀者將研究當(dāng)成放棄減肥的理由，再不想費(fèi)勁了。他們的想法是，“如果減肥成果沒(méi)法保持，為什么還要拼命努力？”

但這種想法忽視一個(gè)重要的細(xì)節(jié)：研究結(jié)束時(shí)，《超級(jí)減肥王》選手體重比參賽前平均減輕了12%，幅度并不小。已有一些研究顯示，只要稍微減點(diǎn)體重，罹患糖尿病、高血壓和心臟病等的幾率就會(huì)明顯下降。

霍爾希望，研究結(jié)果可以讓人們重新思考減肥方式，而不是絕望。他希望把減肥的塑身效果與增進(jìn)健康的功效區(qū)分開(kāi)來(lái)。塑身通常需要大幅減重，很難長(zhǎng)期保持（體重降到一定程度，就會(huì)啟動(dòng)人體內(nèi)部的“彈簧”，體重會(huì)開(kāi)始惡性反彈）。而增進(jìn)健康只要將減重控制在一定范圍內(nèi)，可以通過(guò)逐漸又合理地改變生活方式實(shí)現(xiàn)。

“《超級(jí)減肥王》之類節(jié)目不斷灌輸概念，即保持身體健康和生活正常就得減掉很多體重，”霍爾說(shuō)，“但如果真為了健康沒(méi)必要迅速瘦身?！痹絹?lái)越多的研究認(rèn)為，體質(zhì)指數(shù)（BMI）低未必健康。瘦人同樣可能得心臟病。而肥胖人士如果不吸煙，堅(jiān)持鍛煉，保持健康飲食，過(guò)早去逝的幾率不會(huì)高于生活習(xí)慣類似的正常體重人士。

霍爾指出，雖然證據(jù)越來(lái)越充分，但真正了解的人不多。無(wú)論是減肥行業(yè)、熱衷報(bào)道成功減掉一半體重的雜志，還是美國(guó)人對(duì)煥發(fā)新生和美貌的迷戀，都在將節(jié)食和鍛煉神化，讓人以為只要努力就能瘦，付出一定有回報(bào)。

何不重新定位健身節(jié)食，別刻意追求好體型，是努力讓生活變得更健康呢？霍爾認(rèn)為，現(xiàn)在就該行動(dòng)起來(lái)了。（財(cái)富中文網(wǎng)）

譯者：Pessy

審稿：夏林

For decades, weight loss advice could be summed up in a sentence: burn more calories than you consume. This equation, based on the 3500 rule, in which a calorie deficit of 3500 translates into weight loss of one pound, was intuitive and comforting in its simplicity.

It also made generations of dieters feel terrible about themselves, essentially conflating excess fat with a failure of willpower. If the 69% of Americans who are overweight or obese could simply eat less and move more, this line of thinking went, we wouldn’t have a national epidemic on our hands. While researchers have been questioning the validity of the 3500 calorie rule for years, it still informs much of the popular understanding on weight and metabolism.

That’s beginning to change, though. Ironically, a major recent revelation came courtesy of the Biggest Loser, an NBC reality series that, perhaps more than anything else on TV, reduces weight loss to a matter of willpower (contestants on the show compete to lose the largest percentage of their body weight over the span of 30 weeks.)

But new research suggests the real narrative is likely far more complex. In the study, published last May, researchers tracked 14 of the shows contestants, measuring their weight, metabolism, fitness schedule and diet before they were officially selected for the series’ eighth season, at various points throughout filming, and then six years after the season ended.

Unsurprisingly, all 14 participants were significantly overweight before their stint on The Biggest Loser — and all lost a significant amount of weight during filming. More surprising was that, but for a single participant, they’d all regained some of this weight by the study’s end, with four participants actually weighing more than they did before going on the show.

The real jaw-dropper? The researchers found that during and after the initial weight loss, participants’ bodies fought to return to their original weights: across the board, after losing weight on the show, participants’ metabolism slowed dramatically, meaning their bodies burned fewer calories than is typical for someone their size. This wasn’t a temporary change, either — as the years passed, not only did their metabolisms not recover but, in many cases, they continued to slow down. At the study’s close, season 8 winner Danny Cahill, who lost 239 pounds on the show and regained 100 of them over the subsequent six years, burned 800 fewer calories per day while at rest than is typical for someone his size.

The results are a strong indicator that weight loss shouldn’t be reduced to a matter of willpower, says lead author Kevin Hall. Instead, “when you cut your calories and increase your physical activity, your body resists that change,” he says. Think of it like a string. If you aren’t trying to lose weight, the string remains slack. But as you cut calories and add exercise, it grows increasingly taut. The more intense your diet and workout gets, the tighter the spring pulls in an effort to return you body to its resting weight.

“You will experience a proportional pullback,” says Hall, which, if you want to successfully keep weight off, you must resist indefinitely. It’s a Catch-22 of sorts. The more successful you are at losing weight, the harder your body will fight to regain it — indeed, participants who lost the most weight on the show experienced the largest slowing in metabolic adaption.

If this sounds like a giant bummer, well — in some ways, it is. Weight loss, the study suggests, is more difficult than simply moving more and eating less. But Hall feels that by focusing on the pounds participant regained, subsequent coverage pushed an overly negative message. Following high-profile write ups, including this one in The New York Times, he noticed a discouraging trend: Readers were interpreting the study as a reason to give up on weight loss efforts, full-stop. “If they couldn’t keep it up,” the thinking went, “that what’s the point of even trying?”

But this ignores an important detail: at the end of the study, participants, on average, were down 12% from their pre-Biggest Loser weights, a not insignificant amount. Studies have shown that for overweight and obese individuals, even small weight losses can significantly reduce the likelihood of developing conditions such as diabetes, hypertension and heart disease.

In lieu of despair, Hall hopes the study will make people to rethink weight loss. More specifically, he wants to separate its cosmetic draw from its ability to improve health. The former, which typically requires a radical reduction of body weight, is nearly impossible to achieve long term (drop below a certain set weight, and the body’s internal spring begins its vicious tugging). But the latter, which requires individuals to lose a far manageable amount of weight, is attainable through gradual, sustainable lifestyle changes.

“Shows like the Biggest Loser help perpetuate that idea that you really need to lose enormous quantities of weight to be healthy and be normal,” says Hall. “But you don’t have to have this rapid or dramatic weight loss to have health benefits.” As an increasing body of research suggests, a low BMI and health are not always correlated. Thin people can have heart attacks, and obese people who exercise, don’t smoke, and maintain a healthy diet are no more likely to die prematurely than normal-weight individuals who fall into the same categories.

Despite the mounting evidence, however, this isn’t a message we hear enough, says Hall. The diet industry, the magazine covers of people shedding half their body weight, an American obsession with rebirth and beauty — all have worked together to turn diet and exercise into magical tools that, if we only work hard enough, will make us thin and worthy.

What if we rebranded exercise and diet not as means to a more attractive-looking end, but as tools for improving our overall fitness and health? Hall believes it's time we started.