什么樣的食物最增肥？

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.

肥胖研究中一個基本且尚未解決的問題是什么樣的食物最導(dǎo)致肥胖。專家們提出的原因各不相同，例如含脂肪或糖的食物或缺乏蛋白質(zhì)的食物，因其可能會在不知不覺中使我們吃得太多。針對任何一個肥胖元兇，都可以匯集不少瑣碎的反駁證據(jù)，但在比較飲食習(xí)慣方面長期且大規(guī)模的實(shí)驗研究卻很少。讓健康的受試者多年暴食某一種食物直到肥胖，這既不道德也不現(xiàn)實(shí)。

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，對小鼠進(jìn)行這種實(shí)驗卻是可能的。今年夏天在《細(xì)胞代謝》雜志(Cell Metabolism)發(fā)表的一項飲食研究中，研究人員隨機(jī)將29種不同飲食中的一種分配給數(shù)百只成年雄性小鼠(科學(xué)家希望在之后的實(shí)驗中納入雌性小鼠)。有些食物以飽和及不飽和脂肪的形式提供最多達(dá)80%的卡路里，碳水化合物則很少;另一些則脂肪很少，大部分由主要來自谷物和玉米糖漿的精制碳水化合物組成，盡管其中有些版本的碳水化合物來自食糖。而另一種飲食的特征是含有極高或極低百分比的蛋白質(zhì)。這些小鼠保持相同的飲食三個月——估計大約相當(dāng)于人類的九年——同時允許它們隨意進(jìn)食和在籠子里走動。然后研究人員測量小鼠的體重和身體組成，并檢查其腦組織是否存在基因活動被改變的證據(jù)。

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.

只有一些小鼠變得肥胖——幾乎全是高脂肪飲食。這些小鼠在與處理獎勵相關(guān)的大腦區(qū)域中也顯示出基因活動被改變的跡象;顯然，肥的食物讓它們開心。其他飲食，包括那些富含食糖的飲食，都沒有導(dǎo)致顯著的體重增加或相同方式的基因表達(dá)改變。即使是含有超過60%脂肪的超高脂肪飲食，也不能顯著增加體重，而且這種飲食中的小鼠比其他同類消耗的食物少，可能是因為它們根本無法吃下如此多的脂肪。這些發(fā)現(xiàn)同樣出現(xiàn)在隨后另外四個鼠科種類的實(shí)驗中。相對高脂肪飲食的雄性小鼠變得肥胖，其他則沒有。

“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.

負(fù)責(zé)該項研究的北京中國科學(xué)院及蘇格蘭阿伯丁大學(xué)教授約翰·斯皮克曼(John Speakman)說：“看起來，如果你是一只小鼠，吃高脂肪的飲食，并且不是極度高脂肪的話，會導(dǎo)致體重增加。”斯皮克曼和他的合著者認(rèn)為，含脂肪膳食刺激并改變了大腦的某些區(qū)域，導(dǎo)致小鼠非常想吃含脂肪食物，以至于忽略了提示它們已經(jīng)攝入足夠能量的其他身體信號。

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.

該研究的重點(diǎn)是體重增加，而不是減少，其受試者顯然是小鼠，而不是人類。但其結(jié)果是提示性的。食糖沒有使小鼠變胖，缺乏蛋白質(zhì)也沒有。只有脂肪使它們變胖。