什么样的食物最增肥？

One fundamental and unanswered question in obesity research is what kind of foods contribute most to the condition. Experts variously blame, for example, fatty or sugary fare or foods that lack protein, which may prompt us, unconsciously, to overeat. Plenty of anecdotal evidence can be marshaled against any of the culprits, but there has been little long-term, large-scale experimental research on people’s comparative eating habits. It is neither ethical nor practical to have healthy subjects gorge themselves on one diet for years until they are obese.

肥胖研究中一个基本且尚未解决的问题是什么样的食物最导致肥胖。专家们提出的原因各不相同，例如含脂肪或糖的食物或缺乏蛋白质的食物，因其可能会在不知不觉中使我们吃得太多。针对任何一个肥胖元凶，都可以汇集不少琐碎的反驳证据，但在比较饮食习惯方面长期且大规模的实验研究却很少。让健康的受试者多年暴食某一种食物直到肥胖，这既不道德也不现实。

It is possible, though, to conduct this sort of experiment on mice. For 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 female mice in later experiments.) Some diets supplied up to 80 percent of their calories in the form of saturated and unsaturated fats, with few carbohydrates; others included little fat and consisted largely of refined carbohydrates, mostly from grains and corn syrup, although in some variations the carbs came from sugar. Yet other diets were characterized by extremely high or low percentages of protein. The mice stayed on the same diet for three months — estimated to be the equivalent of roughly nine human years — while being allowed to eat and move about their cages at will. The mice were then measured by weight and body composition, and their brain tissue was examined 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 of the mice became obese — almost every one of which had been on a high-fat diet. These mice showed signs of changes in the activity of certain genes too, in areas of the brain related to processing rewards; fatty kibble made them happy, apparently. None of the other diets, including those rich in sugar, led to significant weight gain or changed gene expression in the same way. Even super-high-fat diets, consisting of more than 60 percent fat, did not lead to significant weight gains, and the mice on those diets consumed less food over all than their counterparts, presumably because they simply could not stomach so much fat. These findings were replicated in subsequent experiments with four other murine breeds. Male mice on relatively high fat diets became obese. The others did not.

只有一些小鼠变得肥胖——几乎全是高脂肪饮食。这些小鼠在与处理奖励相关的大脑区域中也显示出基因活动被改变的迹象;显然，肥的食物让它们开心。其他饮食，包括那些富含食糖的饮食，都没有导致显著的体重增加或相同方式的基因表达改变。即使是含有超过60%脂肪的超高脂肪饮食，也不能显著增加体重，而且这种饮食中的小鼠比其他同类消耗的食物少，可能是因为它们根本无法吃下如此多的脂肪。这些发现同样出现在随后另外四个鼠科种类的实验中。相对高脂肪饮食的雄性小鼠变得肥胖，其他则没有。

“It looks like consuming high-fat diets, if they aren’t extremely high fat, leads to weight gain, if you are a mouse,” says John Speakman, a professor at the Chinese Academy of Sciences in Beijing and at the University of Aberdeen in Scotland, who oversaw the study. Speakman and his co-authors believe that the fatty meals stimulated and altered parts of the brains, causing the mice to want fatty food so much that they ignored other bodily signals indicating that they had already 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 was focused on weight gain, not loss, and its subjects were mice, of course, not humans. But the results are suggestive. Sugar did not make the mice fat, and neither did protein deficits. Only fat made them fat.

该研究的重点是体重增加，而不是减少，其受试者显然是小鼠，而不是人类。但其结果是提示性的。食糖没有使小鼠变胖，缺乏蛋白质也没有。只有脂肪使它们变胖。