First doctor: “This morning for breakfast he requested something called ‘wheat germ, organic honey and tiger’s milk.’”

医生甲说：“那家伙说今天早餐想吃……某种叫做‘小麦胚芽、有机蜂蜜和Tiger's Milk有机蛋白质营养棒’的东西。”

Second doctor: “Oh, yes. Those are the charmed substances that some years ago were thought to contain life-preserving properties.”

医生乙：“对啊。很多年前，人们对这些东西可着迷啦，他们笃信这里面含有维持生命必备的营养成分。”

Fans of Woody Allen may recognize that snippet of dialogue from his 1973 comedy, “Sleeper.” The main character, a health-food store owner somehow frozen in 1973, has been thawed out 200 years later. He awakens to a world he can barely fathom, down to the kinds of food now said to constitute a sound diet. Everything that nutrition specialists once said was good for you, or really bad, turned out to be wrong.

如果你是伍迪·艾伦(Woody Allen)的粉丝，或许你已经认出上述对话是他1973年的喜剧电影《傻瓜大闹科学城》(Sleeper)中的片段。影片的主角是一名健康食品商店的老板，1973年他莫名其妙地被冷冻了起来，直到200年后才被解冻。他苏醒过来，发现自己来到了一个令他迷惑不解的新世界，就连所谓的“健康食品”也改变了——过去被营养专家宣称是对人大有益处或害处的东西，后来发现都不是那么回事儿。

First doctor: “You mean there was no deep fat? No steak or cream pies or hot fudge?”

医生甲：“你是说，不包括油炸食品？也没有牛排、奶油馅饼或热巧克力？”

Second doctor: “Those were thought to be unhealthy — precisely the opposite of what we now know to be true.”

医生乙：“他们觉得这些东西不健康——不过，我们现在知道，事实恰恰相反呀。”

Moviegoers laughed. They recognized how they were whipsawed by contradictory expert pronouncements about what they should or should not eat to stay healthy. On this score, not much has changed. How many times have Americans read about a study damning this or that food, only to then hear the revisionist opposite? Avoid eggs, we were told; they clog your arteries. Wait, we then heard, eggs have nutritional value. Coffee can give you cancer. Hold on, coffee can improve brain function. Butter is terrible. Well, not really. Again and again, yesterday’s verity becomes today’s punch line.

看到这里，观众们纷纷大笑起来。他们意识到，关于为了保持健康应该或不应该吃什么，专家们一直在给他们灌输相互矛盾的意见，让他们莫衷一是——只有这一点似乎一直都没有改变。多少次，一项研究言之凿凿，宣称这种或那种食物“罪大恶极”，结果不久，就又有人提出相反的论断。我们被告知不要吃鸡蛋，因为它们会堵塞你的动脉——接着我们又听说，鸡蛋颇具营养价值；咖啡会害你患癌症——等等，咖啡可以改善脑功能；黄油简直糟透了——好吧，其实也并非如此。一次又一次，昨天被奉为至理名言的，变成了今天的笑话。

The vagaries of nutrition claims infuse the latest episode of Retro Report, video documentaries exploring major news developments of the past and how they still resound. This installment harks back to the 1970s, when many health authorities asserted, with unshakable confidence, that a diet low in fat and cholesterol was essential for a healthful life (wheat germ and tiger’s milk presumably optional).

最近一期的“Retro Report”（回顾历史上的重大新闻，并探讨其现实意义的系列电视纪录片）中就充斥着此类变幻莫测的营养学声明。这期节目回顾了上世纪70年代，当时，众多卫生部门都以坚不可摧的信心声称，低脂肪和低胆固醇的饮食（譬如小麦胚芽和Tiger's Milk有机蛋白质营养棒之类）是健康生活必不可少的一部分。

“Fat-free” became a mantra, not to mention a marketing tool to sell breakfast cereals and high-caloric snacks. If anyone qualified as a heretic back then, it was Dr. Robert C. Atkins, a cardiologist who died in 2003. The Atkins diet encouraged loading up on fat-laden foods like steaks and omelets, and steering clear of pasta, bread and other carbohydrates.

“脱脂”仿佛成了一个魔咒，更不用说它实际上已经化身为推销早餐谷物和高热量小食品的一种营销工具。而在当年，要说特立独行离经叛道，当属心脏病医生罗伯特·C·阿特金斯(Robert C. Atkins)博士了（他在2003年去世）。阿特金斯饮食法鼓励人们大量进食高脂肪食物，如牛排和煎蛋卷等，同时避免食用意面、面包等碳水化合物。

But conventional wisdom held that fat was bad, period, with relatively few Americans distinguishing between saturated fats (meat, eggs, dairy products) and healthier unsaturated fats (fish, vegetable oils, nuts). Typically, people turned to breads, cereals and potatoes — and to sugary soft drinks — for the calories they no longer got from protein-rich foods.

但传统观念认为脂肪不是好东西，句号，一度只有少数美国人能对饱和脂肪（肉、蛋、乳制品）和较为健康的不饱和脂肪（鱼、植物油、坚果）区别对待。通常，人们只是直接转而食用面包、谷物、土豆以及含糖软饮料，以便获得他们原本应从富含蛋白质的食物中摄取的热量。

“Diet is a trade-off,” Gary Taubes, a science journalist and the author of “Why We Get Fat,” told Retro Report. “If we reduce the amount of fat, you have to replace it with something.” That something tended to be carbohydrates. The result? Carbo-loading Americans grew fatter. “We put the whole country on a low-fat diet,” Mr. Taubes said, “and, lo and behold, we have an obesity epidemic.”

“膳食是个交易过程，”《我们为什么会发胖？》(“Why We Get Fat”)一书的作者，科学记者盖里·陶比斯(Gary Taubes)在接受”Retro Report”采访时说。“如果我们减少了脂肪的摄入量，就必须用别的什么东西来替代它。”——比如碳水化合物。结果，大量食用碳水化合物，让美国人变得更胖了。陶比斯先生说：“在整个国家推行低脂肪饮食后，瞧啊，肥胖大肆流行了开来。”

Obesity has proved a stubborn plague, one that the Centers for Disease Control and Prevention says affects 35 percent of American adults — about 79 million people. Tens of millions more, while not technically obese, are overweight. Not coincidentally, diabetes is a big national headache, even if the C.D.C. reported last month that new cases of the disease had begun to decline.

肥胖已成为一个顽疾，美国疾病控制和预防中心(Centers for Disease Control and Prevention，CDC)的工作人员表示，在美国的成年人中，肥胖者人数高达7900万，占35%。还有数以千万计的人虽然严格来说算不上肥胖，至少也是超重的。无独有偶，虽然据CDC上个月报道，糖尿病的新病例数开始下降了，但它仍是令美国头痛的一大疾病。

As for that low-fat diet, a major federal study concluded in 2006 that its health benefits were greatly overrated. Such a diet, researchers found, had no effect on the risk of heart disease or cancer, the two biggest killers in the United States

2006年美联邦进行的一项重大研究显示，低脂肪饮食的健康效益被大大高估了。研究人员发现，这种饮食对美国致死率最高的两大疾病——心脏病和癌症的风险并没有影响

This Retro Report episode comes as the federal government is again rethinking its Dietary Guidelines for Americans. They form a nutrition template that Washington issues every five years and is a bible for millions of the diet-conscious, whose numbers undoubtedly include many who overindulged during the holidays and entered the new year with a pledge to shed pounds.

本期“Retro Report”的推出，正值联邦政府再次反思其《美国膳食指南》(Dietary Guidelines for Americans)之际。这些每隔五年由华盛顿发布的指南得到了数以百万计的注重饮食者的追捧，并视其为营养模板和饮食圣经，毫无疑问，众多在节假日里胡吃海喝，而后又在新年伊始许愿一定要减肥的人也在其中。

The new guidelines are expected to be issued this month by the Departments of Agriculture and of Health and Human Services, which tend to follow the recommendations of an advisory committee. One likely eye-catcher is a new assessment of cholesterol, long an archvillain. It seems destined for rehabilitation to some degree. Months ago, the advisory committee concluded that the dietary intake of cholesterol (the body produces this waxy, artery-obstructing matter on its own) had no real effect on blood levels of LDL, the so-called bad cholesterol. “Cholesterol,” the committee said, “is not a nutrient of concern for overconsumption.”

预计新指南将在本月由美国卫生和公众服务部(Department of Health and Human Service)和农业部(Department of Agriculture)发布。这些指南通常都会遵循顾问委员会的建议。其中，一项关于胆固醇的新评估很可能将十分引人注目。长期以来，胆固醇一直被视为洪水猛兽，而该评估可以说在一定程度上为它平了反。几个月前，该顾问委员会得出结论，从膳食中摄取胆固醇（人体自己也会产生这种会阻塞动脉的蜡状物）对LDL（低密度脂蛋白胆固醇），也就是所谓的“坏胆固醇”的血液浓度没有实质影响。该委员会称：“我们无需担心过度摄取胆固醇。”

There is a conspicuous American tendency to cling to a favored diet as the gateway to good health, keeping weight down, staving off cancers and banishing heart attacks. A consequence is an abundance of regimens — vegan, gluten-free, Paleolithic, fruitarian and many more — each promoted by its adherents as the one true path.

美国人中存在着一种非常明显的倾向，总是喜欢追捧某种特殊的饮食，以为它是能让你身体健康、保持体重、预防癌症、避免心肌梗死的唯一制胜法宝。结果，各种各样的膳食方案层出不穷：素食主义、无麸质饮食、旧石器时代饮食（Paleolithic，又译，古式饮食）、果食主义等等，每一种都拥有大批忠贞不二的拥趸。

But nutrition experts, including those in this Retro Report, caution that life is complex, and that we are more than what we eat. Among them is Dr. Barbara V. Howard, who was a principal investigator in the 2006 federal study of low-fat diets.

但营养专家，包括本期“Retro Report”中的专家们都警告，生命远比吃什么东西复杂得多。芭芭拉·V·霍华德(Barbara V. Howard)博士也是其中之一，她是2006年美联邦一项低脂肪饮食研究的首席研究员。

“We are not going to reverse any of the chronic diseases in this country by changing the composition of the diet,” Dr. Howard said when that report was issued. “People are always thinking it’s what they ate. They are not looking at how much they ate, or that they smoke or that they are sedentary.”

“在这个国家中，改变饮食结构是无法逆转任何慢性疾病的，”霍华德博士在发布上述研究报告时说道。“人们总觉得问题出在食物身上，却从不留心自己的食量，以及吸烟与否或是否存在久坐不动的生活习惯等。”

Other explanations for why one person gains weight and someone else does not may include sleep patterns, genetic predispositions and the compositions of individual microbiomes — the trillions of microbes residing inside the human body. Some health researchers even question the significance of exercise in keeping pounds off, regardless of its other benefits. Among other things, one has to move around quite vigorously to hold the weight down. A Big Mac, for instance, has 540 calories. To burn it off, a person would need to jog or to swim laps for about 45 minutes. Not every Big Mac eater exercises that strenuously.

对于为何有些人容易发胖而其他人则不然，还有些其他的解释，例如睡眠模式、遗传倾向和个人的微生物组（也就是栖息在人体内的数万亿微生物的总和）等。有些健康研究人员甚至对运动在保持体重中的重要性提出了质疑——虽然他们承认它可以带来其他好处。别的先不说，要控制体重，一个人非积极地运动不可。例如，一个巨无霸(Big Mac)含有540卡路里的热量。要消耗掉这些热量，需要慢跑或游泳45分钟。显然，不是每个吃巨无霸的人都会这么勤奋地锻炼的。

Politics, too, can enter the picture. An example is the experience of Michael R. Bloomberg, a forceful public-health advocate when he was New York’s mayor. Despite resistance from restaurant owners and their political allies, Mr. Bloomberg pushed through a ban on trans fats (almost universally deemed a health hazard), and required fast-food outlets to post calorie counts.

政治在饮食问题中也占有一席之地。就拿迈克尔·R·布隆伯格(Michael R. Bloomberg)的经历为例吧，他在担任纽约市长时是一位强有力的公众健康倡导者。尽管遭遇了来自餐馆老板和他们的政治盟友的阻力，布隆伯格依然力促通过了对反式脂肪（普遍认为它有害健康）的禁令，并要求快餐店公布其产品的卡路里计数。

But he hit a political and a juridical wall when he also sought to restrict the sale of sodas and other sugary drinks of dubious nutritional value. State courts shot down his plan on procedural grounds. Mr. Bloomberg found himself widely denounced for having taken government nannyism too far.

然而，当他试图限制汽水和其他营养价值存疑的含糖饮料的销售时，在政治和法律两方面都碰了壁。州法院基于程序上的原因驳回了他的议案。布隆伯格也因为让政府害了“奶妈主义”病（nannyism，禁止任何“可能”导致伤害的事情——译注）而广受批评。

Then again, no one ever said figuring out the elements of a healthy diet would be easy. Dr. Dariush Mozaffarian, a nutrition specialist at Tufts University, suggested to Retro Report that accepted wisdom was not necessarily wise. Much of what has shaped dietary guidelines, he said, are “basically best guesses.” Uncertainty abounds. “I think now we know about 50 percent of what we need to know,” Dr. Mozaffarian said.

不过话说回来，要找到健康饮食的要素绝非易事。塔夫茨大学(Tufts University)的营养学专家戴瑞什·莫萨法利安(Dariush Mozaffarian)博士向“Retro Report”表示，受到广泛认可的观念未必就是正确的。他说，膳食指南中的大部分内容“基本上都是些‘最佳猜测’(best guess)，”充满了不确定性。他还说：“我认为我们目前所知的，只占应该和需要知道的50%左右。”

So is it possible that steaks, cream pies and hot fudge will someday be called the cornerstones of a healthy diet? Maybe if you can stick around for 200 years, you’ll find out.

既然如此，有朝一日人们会不会将牛排、奶油馅饼和热巧克力列为健康饮食的重要组成部分？努力再活上个200年，你就知道啦。