爲什麼運動不一定會減肥?
Governments are always telling us to eat less and exercise more to be healthier, but this presents an obvious problem.
政府總是告訴我們要少吃多運動才能更健康，但這卻有一個明顯的問題。Being active is liable to make you hungrier, so there's a risk you end up eating extra to compensate, and putting on more weight than if you'd never got off the sofa in the first place.
運動容易讓你更餓，以至於你可能會吃更多東西來補充（體力），比你一開始就沒有從沙發上起身要增重更多。Dieticians dream of the day when they can design diets for people where they are more active but don't get hungry in the process.
營養師夢想着有一天，他們可以爲人們設計飲食，使他們更積極地參與運動，卻不會感到飢餓。
Unfortunately it's trickier than you might think: we're still searching for the mechanism that governs how the energy we expend translates into our level of appetite. And as we shall see, that's by no means the only thing that makes this area complicated.
不幸的是，這比你想象的要複雜得多：我們仍然在探求把我們消耗的能量轉化成食慾的機制。正如我們將看到的一樣，這絕不是使這個領域變得複雜的唯一原因。In an ideal world, the human body would be wired to immediately detect changes in the amount of energy we use and then give us the appetite to eat the right amount to balance it out.
在理想的世界裏，人類的身體會立即檢測出我們消耗的能量的變化，然後讓我們有胃口吃適量的食物來相抵。
Alas not: we all get hungry two or three times a day, sometimes more, regardless of what we are getting up to.
可惜的是：不管我們做什麼，我們每天都會餓上兩三次，有時候會更多。Our bodies also release far stronger signals about our appetite when we haven't eaten enough than when we've eaten too much.
與我們吃得過多的時候相比，在我們吃得不夠的時候，我們的身體會釋放出更強烈的食慾信號。This poor daily feedback relationship helps to explain why obese people still experience strong feelings of hunger – that and all the cheap calorie-dense food that is widely available, of course.
這種糟糕的日常反饋關係有助於解釋爲什麼肥胖的人仍然有強烈的飢餓感，以及那些廉價的高熱量食物爲什麼會隨處可見。What could lie behind this difference? One possibility is that physiological processes change in people who do more exercise – for instance, their gut hormones might be released in different concentrations when they eat, potentially with a bearing on how much food they need.
造成這種差異的原因是什麼呢？一種可能是，運動多的人的生理過程會發生變化。例如，他們進食時釋放的腸道激素濃度可能會不同，這可能與他們需要多少食物有關。One longstanding question, dating back some 60 years, is where metabolism fits into the picture. Some important work published in 2013 by a team in Leeds found that overweight people were hungrier and consumed more calories than thinner people.
一個存在已久的問題是，新陳代謝在其中起到了什麼作用，這一問題可追溯至大約60年前。利茲的一個研究團隊在2013年發表的重要研究表明，太胖的人比消瘦的人更容易餓，攝入的熱量也更多。
