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简介：在美国，80%的女孩在她们10岁的时候便开始节食。神经学家Sandra Aamodt结合自己的亲身经历，讲述大脑是如何控制我们的身体的。节食减肥为何没效果?来听听她的说法吧!Three and a half years ago, I made one of the best decisions of my life. As my New Years resolution, I ge up dieting, stopped worrying about my weight, and learned to eat mindfully. Now I eat whenever Im hungry, and Ive lost 10 pounds.This was me at age 13, when I started my first diet. I look at that picture now, and I think, you did not need a diet, you needed a fashion consult. (Laughter) But I thought I needed to lose weight, and when I gained it back, of course I blamed myself. And for the next three decades, I was on and off various diets. No matter what I tried, the weight Id lost always came back. Im sure many of you know the feeling.As a neuroscientist, I wondered, why is this so hard? Obviously, how much you weigh depends on how much you eat and how much energy you burn. What most people dont realize is that hunger and energy use are controlled by the brain, mostly without your awareness. Your brain does a lot of its work behind the scenes, and that is a good thing, because your conscious mind -- how do we put this politely? -- its easily distracted. Its good that you dont he to remember to breathe when you get caught up in a movie. You dont fet how to walk because youre thinking about what to he for dinner.Your brain also has its own sense of what you should weigh, no matter what you consciously believe. This is called your set point, but thats a misleading term, because its actually a range of about 10 or 15 pounds. You can use lifestyle choices to move your weight up and down within that range, but its much, much harder to stay outside of it. The hypothalamus, the part of the brain that regulates body weight, there are more than a dozen chemical signals in the brain that tell your body to gain weight, more than another dozen that tell your body to lose it, and the system works like a thermostat, responding to signals from the body by adjusting hunger, activity and metabolism, to keep your weight stable as conditions change. Thats what a thermostat does, right? It keeps the temperature in your house the same as the weather changes outside. Now you can try to change the temperature in your house by opening a window in the winter, but thats not going to change the setting on the thermostat, which will respond by kicking on the furnace to warm the place back up.Your brain works exactly the same way, responding to weight loss by using powerful tools to push your body back to what it considers normal. If you lose a lot of weight, your brain reacts as if you were starving, and whether you started out fat or thin, your brains response is exactly the same. We would love to think that your brain could tell whether you need to lose weight or not, but it cant. If you do lose a lot of weight, you bee hungry, and your muscles burn less energy. Dr. Rudy Leibel of Columbia University has found that people who he lost 10 percent of their body weight burn 250 to 400 calories less because their metabolism is suppressed. Thats a lot of food. This means that a successful dieter must eat this much less forever than someone of the same weight who has always been thin.From an evolutionary perspective, your bodys resistance to weight loss makes sense. When food was scarce, our ancestors survival depended on conserving energy, and regaining the weight when food was ailable would he protected them against the next shortage. Over the course of human history, starvation has been a much bigger problem than overeating. This may explain a very sad fact: Set points can go up, but they rarely go down. Now, if your mother ever mentioned that life is not fair, this is the kind of thing she was talking about. (Laughter) Successful dieting doesnt lower your set point. Even after youve kept the weight off for as long as seven years, your brain keeps trying to make you gain it back. If that weight loss had been due to a long famine, that would be a sensible response. In our modern world of drive-thru burgers, its not working out so well for many of us. That difference between our ancestral past and our abundant present is the reason that Dr. Yoni Freedhoff of the University of Ottawa would like to take some of his patients back to a time when food was less ailable, and its also the reason that changing the food environment is really going to be the most effective solution to obesity.Sadly, a temporary weight gain can bee permanent. If you stay at a high weight for too long, probably a matter of years for most of us, your brain may decide that thats the new normal.Psychologists classify eaters into two groups, those who rely on their hunger and those who try to control their eating through willpower, like most dieters. Lets call them intuitive eaters and controlled eaters. The interesting thing is that intuitive eaters are less likely to be overweight, and they spend less time thinking about food. Controlled eaters are more vulnerable to overeating in response to advertising, super-sizing, and the all-you-can-eat buffet. And a small indulgence, like eating one scoop of ice cream, is more likely to lead to a food binge in controlled eaters. Children are especially vulnerable to this cycle of dieting and then binging.