THE answer to obesity is obvious: eat less and exercise more. However, years of exhortation have failed to persuade most of those affected actually to do this. 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. Oddly, though, a convenient mathematical model describing this fact has yet to be widely adopted. But a paper in this week's Lancet, by Kevin Hall of America's National Institutes of Health (NIH) and his colleagues, aims to change that.

【翻譯參考】
減肥的方法顯而易見，就是少吃多運動。然而，這一方法在過去這么多年中并沒有說服大多數的肥胖者去付諸行動。特別是，減去已經堆積起來的脂肪遠比避免長出多于脂肪困難得多。奇怪的是，盡管有這樣一個的便利的數學模式來描述這一事實，但是它卻并沒有被廣泛接受。但是發表在本周Lancet雜志上的一篇論文卻試圖改變這一情況。該文是由美國國家衛生研究院的Kevin Hall和他的同事共同撰寫完成。

【好詞好句】
1. sth fails to do sth
相對應的 success in doing sth
2. have the benefit of sth/doing sth 有......好處， 有利于
不要總是用sth is good for 了
3. account for 考慮到，鑒于
4. it acknowledges that 承認（不過 it is acknowledged that 這個句型更常見）
5. in stages 有階段性的
6. a will of iron 鋼鐵般的意志

【summary】
The difficulty of losing weight is captured in a new model.

The conventional rule for slimming, espoused by both the NIH and Britain's National Health Service, has the benefit of simplicity: cut 500 calories each day and lose half a kilo (about a pound) a week. 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. Dr Hall's model tries to do this. It also accounts for baseline characteristics that differ from person to person. 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. The result is a more realistic assessment of what someone needs to do to get slim.