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  One of the basic and unsolved questions in obesity research is what kind of food causes the most obesity. Experts put forward different reasons, such as foods that contain fat or sugar or foods that lack protein, because they can cause us to eat too much without even knowing it. There is plenty of anecdotal evidence against any of the culprits, but there have been few long-term, large-scale studies comparing eating habits. It is neither ethical nor realistic to ask healthy subjects to binge on a certain food for years until they become obese.


  But it is possible to do this in mice. In a diet study published this summer in Cell Metabolism, researchers randomly assigned one of 29 different diets to hundreds of adult male mice (the scientists hope to include females later in the experiment). Some foods provide up to 80 percent of calories in the form of saturated and unsaturated fats and very few carbohydrates. Others have less fat and are mostly made up of refined carbohydrates, mainly from grains and corn syrup, although some versions of these carbohydrates come from sugar. Another diet is characterized by a very high or very low percentage of protein. The mice were kept on the same diet for three months -- about nine human years, by some estimates -- while being allowed to eat and move around the cage as they liked. The researchers then measured the mice's weight and body composition and examined their brain tissue for evidence of altered gene activity.

  但是,对小鼠进行这种实验却是可能的。今年夏天在《细胞代谢》杂志(Cell Metabolism)发表的一项饮食研究中,研究人员随机将29种不同饮食中的一种分配给数百只成年雄性小鼠(科学家希望在之后的实验中纳入雌性小鼠)。有些食物以饱和及不饱和脂肪的形式提供最多达80%的卡路里,碳水化合物则很少;另一些则脂肪很少,大部分由主要来自谷物和玉米糖浆的精制碳水化合物组成,尽管其中有些版本的碳水化合物来自食糖。而另一种饮食的特征是含有极高或极低百分比的蛋白质。这些小鼠保持相同的饮食三个月——估计大约相当于人类的九年——同时允许它们随意进食和在笼子里走动。然后研究人员测量小鼠的体重和身体组成,并检查其脑组织是否存在基因活动被改变的证据。

  Only some mice became obese -- almost entirely on a high-fat diet. The mice also showed signs of altered gene activity in brain regions associated with processing rewards; Apparently, fat food makes them happy. Other diets, including those rich in sugar, did not result in significant weight gain or similar changes in gene expression. Even a super-high-fat diet containing more than 60 percent fat did not significantly increase weight, and the mice on this diet consumed less food than their peers, probably because they could not eat so much fat. These findings also emerged in subsequent experiments with four other mouse species. Male mice on a relatively high-fat diet became obese, while others did not. 纽约时报中英文网 http://www.qqenglish.com


  It looks like if you're a mouse and you're on a high-fat diet, and it's not extremely high-fat, it's going to lead to weight gain, said John Speakman, a professor at the Chinese Academy of Sciences in Beijing and at the university of Aberdeen in Scotland, who led the study. Spiekman and his co-authors believe that a fatty diet stimulates and alters certain areas of the brain, causing the mice to crave fatty foods so much that they ignore other body signals indicating they have consumed enough energy.

  负责该项研究的北京中国科学院及苏格兰阿伯丁大学教授约翰·斯皮克曼(John Speakman)说:“看起来,如果你是一只小鼠,吃高脂肪的饮食,并且不是极度高脂肪的话,会导致体重增加。”斯皮克曼和他的合著者认为,含脂肪膳食刺激并改变了大脑的某些区域,导致小鼠非常想吃含脂肪食物,以至于忽略了提示它们已经摄入足够能量的其他身体信号。

  The study focused on weight gain, not loss, and its subjects were apparently mice, not humans. But the results are suggestive. Sugar did not make the mice fat, nor did a lack of protein. Only fat makes them fat.




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