Why We're Fat
1 So why is obesity happening? The obvious, clichéd-but-true answer is that we eat too much high-calorie food and don't burn it off with enough exercise. If only we had more willpower, the problem would go away. But it isn't that easy.
为什么会有肥胖症？一个明显、老生常谈但又真实的答案就是我们吃太多高热量食物并且没有进行足够的运动消耗它。要是我们的意志力更强大，这个问题便迎刃而解了。但是，问题并不是那么简单。
2 When warned about the dangers of overeating, we get briefly spooked and try to do better. Then we're offered a plateful of pancakes smothered in maple syrup, our appetite overpowers our reason, and before we know it, we're at it again. Just why is appetite such a powerful driver of behavior, and, more important, how can we tame it? 当我们被警告说吃得太多的时候，一时总会被吓倒并努力做好一些。然后一碟涂满槭糖浆的煎饼摆在面前，我们的食欲战胜了我们的理智，等到我们意识到它的时候，我们又重蹈覆辙了。到底为什么食欲具有如此强大的推动力？更重要的是，我们怎么才能够控制它？
3 Within the past few years, science has linked our ravenous appetites to genes and hormones. Among the hormones that fuel these urges are ghrelin and leptin, known as the "hunger hormones." Ghrelin is produced mostly by cells in the stomach lining. Its job is to make you feel hungry by affecting the hypothalamus, which governs metabolism. Ghrelin levels rise in dieters who lose weight and then try to keep it off. It's almost as if their bodies are trying to regain the lost fat. This is one reason why it's hard to lose weight and maintain the loss.
近几年来，科学将我们迫不及待要吃的食欲跟基因和激素联系起来。激起这些强烈的欲望的激素有胃促生长素和消瘦素，也被称作“饥饿激素”。胃促生长素主要由胃保护层的细胞产生。它的职责是影响控制新陈代谢的下丘脑，让你感到饥饿。当节食者减肥并且努力维持减肥效果，他的胃促生长素水平就会升高。就像他们的身体要试图恢复失去的脂肪。这是为什么很难减肥并维持减肥效果的原因之一。
4 Leptin turns your appetite off and is made by fat cells. Low leptin levels increase your appetite and signal your body to store more fat. High leptin levels relay the opposite signal. Many obese people have developed a resistance to the appetite-suppressing effects of leptin and never feel satisfied, no matter how much they eat. Basically, your body uses these hormones to help you stay at your weight and keep you from losing fat —which is another reason why dieting can be so difficult.
消瘦素消除你的食欲，它来自脂肪细胞。低消瘦素水平增加你的食欲并通知你的身体储存更多的脂肪。高消瘦素水平传递相反的信号。很多肥胖的人已经形成了一种对消瘦素抑制食欲效应的抵抗，不管他们吃多少也从不感到满足。从根本上说，你的身体利用这些激素帮助你保持现在的体重，不让你的脂肪流走——这是节食如此之难的另外一个原因。
5 Lack of sleep promotes obesity by messing with these hunger hormones. If you skimp on sleep, ghrelin levels rise, making you hungry, and leptin levels dip, which signals a need for calories. During my internship, I was chronically sleep-deprived because I had to be at the hospital and stay up all night every third night. I gained a lot of weight that year; now I know why. Years later, after I gave birth to my son Alex, I put on a lot of pounds, too —twenty pounds left over from the pregnancy, and twenty pounds from being up all night with him. He had colic (fussiness) and never slept more than twenty minutes at a time the first six months of his life. My weight started coming off more easily when I got more sleep.
睡眠缺失促进肥胖，因其干扰了这些饥饿激素。如果你克扣了睡眠时间，胃促生长素水平升高，使你饥饿，并且消瘦素下降，标志着需求热量。在实习期间我长期缺觉，因为每隔三个晚上我得通宵熬夜待在医院里。那年我的体重增加了不少，现在我明白为什么了。在那几年之后，我生了儿子亚力克斯后又增了好多磅——怀孕期间残留的二十磅，还有夜夜无眠陪着他的二十磅。他有急性腹痛且在他生命中的头六个月从未试过连续睡二十分钟以上。当我有了更多睡眠时间，我的体重开始更容易降下来。
6 Besides ghrelin and leptin, many other hormones play a role in appetite. Scientists have been looking for ways to control all these hunger hormones, but so far nothing usable has panned out.
除了胃促生长素和消瘦素，很多其他的激素对食欲也有影响。科学家一直在寻找控制这些饥饿激素的方法，但是目前还没有成果。
7 Hunger isn't the only reason people eat and eat and eat. Stress, depression, boredom, loneliness, and even joy all come into play. And some of us may just be inclined to gain weight while others are not, due to genetics. Scientists are unclear as to how much of a role genetics plays in how chubby you are, but estimates range from as low as 20 percent to as high as 90 percent. In studies of twins, researchers have found that siblings wind up with similar body weights, whether or not they are raised in different families, and that adopted children are much more likely to grow to the size of their natural parents than their adoptive ones. Scientists speculate that part of the reason so many of us are susceptible to layering on fat is due to the "thrifty gene." Supposedly, it's a gene passed down from our prehistoric ancestors who could eat a lot and build up reserves of fat to survive frequent famines. Genetically, this made sense when you didn't know if your next meal would be tomorrow or a week from now, but when your next meal is whenever you drive by a fast-food restaurant, that's a problem.
饥饿不是人们不停地吃的唯一原因。压力，抑郁，无聊，孤独，甚至高兴都会起作用。有些人可能就是易于发胖而另一部分人不会，这应归于遗传。科学家不确定遗传在肥胖上面起多大的作用，但是预测它所占比例从最低20％到最高90％。在对双胞胎的研究中，研究人员发现双胞胎兄弟（或姐妹）最终会有相似的体重，不论他们是不是在不同的家庭中长大，而且收养的小孩的体形大小更可能长成和他们亲生父母的一样。科学家推断我们那么多人易于堆积脂肪的部分原因在于
