評論
打印
Science and technology
科學技術
Obesity
肥胖
A wide spread problem
一個普遍的問題
The difficulty of losing weight is captured in a new model
新模式解讀減肥難題
THE answer to obesity is obvious: eat less and exercise more.
減肥的辦法很明顯：少吃，多運動。
However, years of exhortation have failed to persuade most of those affected actually to do this.
年的忠告并沒有說服大多數肥胖之人踐行這一點。
In particular, it is much harder to shift surplus lard once it has accumulated than it is to avoid putting it on in the first place.
尤其是與避免累積脂肪相比，轉化多余的累積脂肪要困難得多。
Oddly, though, a convenient mathematical model describing this fact has yet to be widely adopted.
不過，奇怪的是講述這個事實的一個簡易數學模式卻沒有被普通采用。
But a paper in this week's Lancet, by Kevin Hall of America's National Institutes of Health and his colleagues, aims to change that.
然而，多但是美國國家衛生研究所的凱文·霍爾及其同事在本周《柳葉刀》上發布的一篇論文旨在改變這種情況。
The conventional rule for slimming, espoused by both the NIH and Britain's National Health Service, has the benefit of simplicity:
美國國家衛生研究所和英國國家衛生服務共同支持的傳統瘦身法具有簡單的優勢：
cut 500 calories each day and lose half a kilo a week.
每天減少500卡路里，每周可減少一斤。
Most experts, though, acknowledge that this rule is too blunt as it fails to account for shifts in the body's metabolism as the kilos pile on.
不過大多數專家都承認，這種方法過于死板，沒有考慮到體重增加時體內新陳代謝的變化。
Dr Hall's model tries to do this.
霍爾博士的模式就是要努力克服這一缺陷。
It also accounts for baseline characteristics that differ from person to person.
該模式還將不同人之間的基本特點考慮在內。
Fat and muscle, for example, respond differently to shifts in diet, so the same intake will have one effect on a podgy person and another on a brawny one.
比如，脂肪和肌肉對飲食變化的反應是不一樣的，因此同樣的攝入量對矮胖子和壯漢的影響也是不一樣的。
The result is a more realistic assessment of what someone needs to do to get slim.
結果是對一個人要瘦身必須要做的事情進行了更加現實的評估。
According to the old version, for example, abstaining from a daily 250-calorie bottle of cola would lead to the loss of 35kg over three years.
比如，根據舊模式，每天少喝一罐250卡路里的可樂，三年體重就可以減輕35公斤。
Dr Hall's model predicts an average loss of just 11kg.
而霍爾博士的模式預測只能平均減少11公斤。
Furthermore, it also acknowledges that a dieter's weight will eventually reach a plateau—far more realistic than the old advice,
此外，它還承認節食者的體重最終將到達穩定階段—比原來的建議要現實得多，
which implied, incorrectly, that weight loss will continue steadily.
原來的建議暗示體重將穩步下降，這是不正確的。
Gaining weight is easy.
增加體重很容易。
A surprisingly small imbalance, just ten extra calories a day, has driven the 9kg jump in the average American's weight over the past 30 years.
非常小的不均衡，不過每天多10卡路里，已經讓美國人的平均體重在過去30年內飆升了9公斤。
The reason reversing such gains is hard is that servicing this extra flesh means a person's maintenance diet creeps up with his weight—and so does his appetite.
恢復原來體重很困難的原因是，為增加的體重提供服務意味著一個人保持體能的飲食與其體重一起增加了，其胃口也增加了。
That 9kg increase implies a daily maintenance diet that has 220 more calories in it than three decades ago.
這增加的9公斤意味著每天保持體能的飲食中的卡路里比30年前多220多卡路里。
Returning to the average of the past means reversing every one of those 220 calories. Half-measures will result in a new equilibrium,
恢復到原來的平均水平意味著每個人要減少220卡路里。
but one that is still too heavy.
減少一半就會達成一種新的平衡，這種平衡仍然會太重。
For example, a 23-year-old man who is 170cm tall should weigh 70kg, and be eating 2,294 calories a day.
比如，一位23歲、升高1.7米的男士的標準體重應該是70公斤，每天攝入2294卡路里。
If he actually weighs 110kg he will be eating 3,080 calories to maintain his extra flesh and he thus needs to make a permanent cut of 786 calories from his daily diet if he is to get back to the 70kg desideratum.
如果他的實際體重是110公斤，那么他必須攝入3080卡路里才能承受額外的負擔。
If he cuts less than this he will lose some weight,
因此如果他要恢復到70公斤的需要，他必須每天減少固定的786卡路里。
but eventually his intake will match the maintenance level for what he now weighs, and without further cuts his weight will stabilise.
如果他減少的卡路里比這個少，他會減少一些體重，但是最終他的攝入量會與他當前的體重匹配，如果不進一步減少，他的體重將穩定下來。
Someone who weighs 90kg, by contrast, need cut only 435 calories a day to get to his target—a far more manageable proposition.
相比之下，體重90公斤的人只需每天減少435卡路里就可以達到他的目標—這是一個要好辦得多的建議。
In principle, the heavier person could make the necessary cuts in stages—reducing his daily intake again and again as he lost weight.
原則上，體重較重的人可以分階段進行必要的節食—在他體重減輕時，不斷減少日常的攝入量。
In practice, that would take a will of iron, and the few people who have such willpower rarely get fat in the first place.
實際上，這需要非常堅定的意志，有這種意志的人幾乎根本就不會變胖。
The lesson, then, is to stay, rather than become, slim.
因此，教訓就是保持苗條而不是變苗條。
Not easy, in a world whose economic imperative is to satisfy every appetite,
在一個經濟動力就是滿足每項欲望的世界里，這并非易事，
but perhaps a little more urgent now Dr Hall has put numbers on it.
但是目前霍爾博士用具體數字對它進行了說明，這樣或許更加緊迫了些。
