关于减肥，我们都想错了

过去几十年所有的减肥建议可以总结为一句话：卡路里消耗大于摄入。这种说法基于卡路里消耗守则，即消耗3500卡路里等于减轻一磅体重。简洁直观，让人感觉减肥并不难。

但这个原则也让无数节食者非常沮丧，因为脂肪超标仿佛等于缺乏意志力。按理说，占美国总人口69%的体重超标人士只要少吃多运动，就不会到处出现肥胖问题。尽管多年来不少科研人员质疑3500卡路里法则，但早已形成人们对体重和新陈代谢的共识。

不过，情况开始变化。讽刺的是，这种新转变的主要推手竟然是一档减肥真人秀节目——美国全国广播公司（NBC）的《超级减肥王》（Biggest Loser）。（要求选手在30周内比赛减肥，减重百分比最高者获胜。）正是这档节目第一次告诉人们减肥与意志力关系没那么紧密。

而新近研究显示，真相可能更加复杂。去年5月发布的一项研究称，研究人士追踪了14位第八季《超级减肥王》参赛者，记录了加入该节目前的体重、新陈代谢水平，健身计划和食谱，在节目录制期间不同时点和第八季结束六年后记录各项水平。

不出所料，所有14名参赛前明显超重，录制节目期间都大幅减重。令人意外的是，除了一位选手，其他13位在研究将近尾声时体重都有所反弹，其中4位选手的体重已超过参赛前。

真正让人大跌眼镜的是，研究人员发现减肥期间和成功减重后，参赛者的身体总在努力恢复原有体重：参赛减重后，选手的新陈代谢水平整体剧减，意思是他们消耗的卡路里低于相同体形常规消耗水平。而且不是短期现象，几年后多数选手的新陈代谢水平非但没能回升，还继续下滑。到研究结束时，减重239磅夺得第八季冠军的丹尼•卡希尔六年内反弹100磅，日均基础热量消耗较同体形人士常规水平少800卡路里。

该研究第一作者凯文•霍尔认为，研究结果明确显示不应把减肥视为只靠意识力就能解决的问题。他解释说：“可以减少摄入卡路里，增加活动，但身体会抗拒改变。” 不妨把人体想象成一根弦。如果你不减肥，弦是松弛的。一旦减少摄入卡路里多运动，弦就绷得越来越紧。瘦身食谱和锻炼越猛，弦就拉得越紧，身体恢复原有体重的反弹力就越大。

“你减肥多努力，阻力就多大。”霍尔说。如果你想保住减肥成果，就得永远跟阻力作斗争。有点像《第22条军规》。减肥越成功，你的身体就越努力恢复原来的体重。事实上，《超级减肥王》节目里减肥最成功的选手赛后新陈代谢水平下降最快。

听起来有点让人绝望，某种程度上的确如此。研究认为，减肥绝非简单地少吃多运动。但霍尔觉得，《超级减肥王》比赛的后续报道把重点放在参赛者复胖，其实夸大了负面影响。他注意到，《纽约时报》等多家媒体高调报道后，出现令人失望的倾向：读者将研究当成放弃减肥的理由，再不想费劲了。他们的想法是，“如果减肥成果没法保持，为什么还要拼命努力？”

但这种想法忽视一个重要的细节：研究结束时，《超级减肥王》选手体重比参赛前平均减轻了12%，幅度并不小。已有一些研究显示，只要稍微减点体重，罹患糖尿病、高血压和心脏病等的几率就会明显下降。

霍尔希望，研究结果可以让人们重新思考减肥方式，而不是绝望。他希望把减肥的塑身效果与增进健康的功效区分开来。塑身通常需要大幅减重，很难长期保持（体重降到一定程度，就会启动人体内部的“弹簧”，体重会开始恶性反弹）。而增进健康只要将减重控制在一定范围内，可以通过逐渐又合理地改变生活方式实现。

“《超级减肥王》之类节目不断灌输概念，即保持身体健康和生活正常就得减掉很多体重，”霍尔说，“但如果真为了健康没必要迅速瘦身。”越来越多的研究认为，体质指数（BMI）低未必健康。瘦人同样可能得心脏病。而肥胖人士如果不吸烟，坚持锻炼，保持健康饮食，过早去逝的几率不会高于生活习惯类似的正常体重人士。

霍尔指出，虽然证据越来越充分，但真正了解的人不多。无论是减肥行业、热衷报道成功减掉一半体重的杂志，还是美国人对焕发新生和美貌的迷恋，都在将节食和锻炼神化，让人以为只要努力就能瘦，付出一定有回报。

何不重新定位健身节食，别刻意追求好体型，是努力让生活变得更健康呢？霍尔认为，现在就该行动起来了。（财富中文网）

译者：Pessy

审稿：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.