Deborah Cohen is a senior natural scientist at the Rand Corp. and the author of the forthcoming book “A Big Fat Crisis: The Hidden Forces Behind the Obesity Epidemic and How We Can End It。”

　　The obesity epidemic is among the most critical health issues facing the United States. Although it has generated a lot of attention and calls for solutions, it also has served up a super-sized portion of myths and misunderstandings。

　　1.If you’re obese, blame your genes。

　　As obesity rates have soared, some researchers have focused on individuals’ genetic predisposition for gaining weight. Yet, between 1980 and 2000, the number of Americans who are obese has doubled — too quickly for genetic factors to be responsible。

　　So why do we eat more than we need? The simple answer: Because we can. At home and at restaurants, a dollar puts more calories on our plates than ever before. Before World War II, the average family spent as much as 25 percent of its total income on food — in 2011, it was 9.8 percent. And people eat out now more than in the past. In 1966, the average family spent 31 percent of its food budget dining away from home — in 2011, it was 49 percent. Because restaurant meals usually have more calories than what we prepare at home, people who eat out more frequently have higher rates of obesity than those who eat out less。

　　Meanwhile, the food industry has developed tens of thousands of products with more calories per bite, as well as new, effective marketing strategies to encourage us to buy and consume more than necessary. We should blame these business practices, which are modifiable, for obesity rather than our genes, which are not。

　　2.If you’re obese, you lack self-control。

　　According to a 2006 study, “research on restrained eating has proven that in most circumstances dieting is not a feasible strategy。” In other words: People won’t lose weight by trying to eat less because they can’t easily control themselves. Unfortunately, this puritanical view of personal resolve plays down how our surroundings and mental state determine what we eat。

　　Research shows that if we are overwhelmed with too much information or preoccupied, we have a tendency to surrender to poor dietary choices. In one study, for example, people asked to choose a snack after memorizing a seven-digit number were 50 percent more likely to choose chocolate cake over fruit salad than those who had to memorize a two-digit number. When adults in another study were asked to sample a variety of foods after watching a television show with junk-food commercials, they ate more and spent a longer time eating than a similar group watching the same show without the junk-food ads. In the same study, children ate more goldfish crackers when watching junk-food commercials than those who saw other ads。

　　Our world has become so rich in temptation that we can be led to consume too much in ways we can’t understand. Even the most vigilant may not be up to the task of controlling their impulses。

　　3. Lack of access to fresh fruits and vegetables is responsible for the obesity epidemic。

　　The Obama administration’s Healthy Food Financing Initiative is meant to help low-income communities that lack access to fresh food. Although the U.S Department of Agriculture estimates that fewer than 5 percent of Americans live in these “food deserts,” about 65 percent of the nation’s population is overweight or obese. For most of us, obesity is not related to access to more nutritious foods, but rather to the choices we make in convenience stores and supermarkets where junk-food marketing dominates. Since we are buying more calories than we need, eating healthfully could be made more affordable by eliminating unnecessary cheaper low nutrient foods and substituting higher quality foods that may be slightly more expensive。

　　Obesity is usually the consequence of eating too much junk food and consuming portions that are too large. People may head to the produce section of their grocery store with the best intentions, only to be confronted by candy at the cash register and chips and soda at the end of aisles. Approximately 30 percent of supermarket sales are from such end-of-aisle locations. Food retailers’ impulse-marketing strategies contribute significantly to obesity across the population, not just for those who do not live near a green grocer or can’t afford sometimes pricier healthy choices。

　　4. The problem is not that we eat too much, but that we are too sedentary。

　　First lady Michelle Obama’s “Let’s Move” campaign is based on the idea that if kids exercised more, childhood obesity rates would decline. But according to the Centers for Disease Control and Prevention, there was no significant decrease in physical activity levels as obesity rates climbed in the 1980s and 1990s. In fact, although a drop in work-related physical activity may account for up to 100 fewer calories burned, leisure physical activity appears to have increased, and Americans keep tipping the scales。

　　There is compelling evidence that the increase in calories consumed explains the rise in obesity. The National Health and Nutrition Examination found that people take in, on average, more than 500 more calories per day now than they did in the late 1970s, before obesity rates accelerated.That’s like having Christmas

　　dinner twice a week or more. It wouldn’t be a problem if we stuffed ourselves only once a year, but all-you-can-eat feasts are now available all the time. It’s nearly impossible for most of us to exercise enough to burn off these excess calories。

　　5. We can conquer obesity through better education about diet and nutrition.. We can conquer obesity through better education about diet and nutrition。

　　According to a physicians’ health study, 44 percent of male doctors are overweight. A study by the University of Maryland School of Nursing found that 55 percent of nurses surveyed were overweight or obese. If people who provide health care cannot control their weight, why would nutrition education alone make a difference for others?

　　Even with more information about food, extra-large portions and sophisticated marketing messages undermine our ability to limit how much we consume. Consider Americans’ alcohol consumption: Only licensed establishments can sell spirits to people older than 21, and no alcohol can be sold in vending machines. Yet there are very few standards or regulations to protect Americans from overeating。

　　In the 19th century, when there were no controls on the quality of drinking water, infectious disease was a major cause of death. Once standards were established, the number of these fatalities plummeted。

　　Similarly, if Americans did not live in a world filled with buffets, cheap fast food, soft drinks with corn syrup, and too many foods with excess fat, salt and sugar, the incidence of obesity, heart disease, high blood pressure and diabetes probably would plummet. Education can help, but what’s really needed is regulation — for example, limits on marketing that caters to our addiction to sugar and fat。

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　　黛博拉•科恩是美国兰德公司一位高级自然科学家，她所著书籍《肥胖危机：肥胖背后隐藏的原因及如何摆脱肥胖》即将出版问世。

　　肥胖症是美国人面临的最严峻的健康问题之一。尽管它已经引起了广泛关注和对治疗办法的诉求，人们对于肥胖症的理解仍然有超大比例的谬见和误解：

　　1.肥胖症来自于基因

　　随着肥胖症比率的飙升，一些研究者开始关注个人基因素质对体重增加的影响。然而，从1980年到2000年，美国肥胖症患者数增加了一倍——基因影响无法导致如此快的增长速度。

　　那为什么我们会摄入超出需求量的食物？答案很简单，因为我们的经济条件允许。在家或者在餐厅，1美元较之以前能将更多的卡路里放入餐盘。二战前，平均每个家庭在食物上花费总收入的25%——而在2011年，只有9.8%。人们现在也比以前更多地外出就餐。1966年，平均每个家庭外出就餐的花费占总食物支出预算的31%——而在2011年，比例达到49%。由于餐厅提供的食物比家里准备的富含更多卡路里，频繁外出就餐的人就比其他人有更高的风险患上肥胖症。

　　与此同时，食品工业生产出数以万计的产品，每一口都有更多的卡路里含量；新型高效的市场营销战略也诱使我们购买、消费超出需求的食物。比起改变不了的基因，我们更应该归咎于这些商业活动，毕竟它们可以为解决肥胖问题做出一些改变。

　　2. 肥胖症来自于自制力的缺乏

　　2006年的一项研究显示，“关于节制饮食的调查已经证明，在大多数情况下节食并不是切实可行的减肥策略。”换句话说，由于人们不能轻易控制自己，吃得少并不能使体重减轻。不幸的是，这种清教徒式的个人决心使得周围环境和精神状态对“吃什么”的决定作用大为减轻。

　　研究表明如果我们被过多信息淹没或者全神贯注做某事时，我们会倾向于向食物投降。举例来说，在一次研究中，熟记过一个7位数的受试者在被要求选择零食时，选择巧克力蛋糕而不是水果沙拉的几率要比那些熟记过一个2位数的受试者高出50%。在另一项研究中，一组成年人在观看过插播有垃圾食品广告的电视节目后被要求选取各种食物，另外一组成年人观看没有广告的相同电视节目，最后第一组成年人在观看后吃得更多、更久。另外，同一项研究还发现，观看垃圾食品广告的儿童比那些看其他广告的吃了更多金鱼饼干。

　　我们生活的世界充满了诱惑，它诱导我们以自身都无法理解的方式过度消费。即使最警惕的人也无法成功控制他们的冲动。

　　3.肥胖症是因为缺少获得新鲜水果蔬菜的渠道

　　奥巴马政府的健康食品融资计划旨在帮助那些无法获取新鲜食物的低收入群体。不过据美国农业部估计，只有不到5%的美国人生活在这样的“食物荒漠”中，约65%的美国人肥胖超重。对于我们大多数人来说，肥胖症跟是否能获取有营养的食物无关，而是跟我们在以垃圾食品为主导市场的便利店或超市做出的购买决定有关。由于我们总是买超出需求的卡路里，因此清除那些不必要的低价格、低营养的食物，用高品质、稍昂贵点的食物代替，会使我们能够更加实惠地健康饮食。

　　肥胖通常是由于消费、食用过多垃圾食品导致的。人们可以怀着美好的意图走向杂货店的农产品区，不过他们必须面对收银台旁边的糖果和过道拐角处的薯片、苏打水。而在超市里大约有30%的商品是被摆放在过道尽头之类的位置。食品零售商们的促销策略显著增加了全部人口的肥胖率，而不仅仅是那些居住远离绿色食品或不能支付偶尔高价的健康食品的人。

　　4. 肥胖症的关键问题不是吃得太多，而是坐得太久。

　　美国第一夫人米歇尔•奥巴马发起的“动起来”活动基于这样一个观点：如果孩子们更多地锻炼，那么儿童肥胖率就会下降。

　　但是美国疾病控制与预防中心的资料显示，上世纪80、90年代的体育锻炼水平并没有显著降低，但肥胖率却有所攀升。其实尽管不做专门的体育运动会减少100卡路里的燃烧，但是一些休闲日常活动仍能增加卡路里的燃烧，而美国人却在持续增重。

　　有令人信服的证据表明卡路里消耗量的增加解释了肥胖症越来越多的原因。国家健康与营养调查发现，与上世纪70年代肥胖症患病率还未增加时相比，人们平均每天会多摄入超过500单位的卡路里。这就相当于我们每周超过两次吃圣诞大餐。如果我们每年仅有一次塞满自己的胃，肥胖就不是问题。但是现在随处随时都可以吃大餐了。得到足够锻炼来消耗完过剩的卡路里，对我们大多数人来说也是几乎不可能的。

　　5. 我们可以通过更好的饮食与营养教育来战胜肥胖。

　　一名内科医生的健康研究结果显示，44%的男性医生体重超标。而马里兰护理大学的一项研究发现接受调查的护士中有55%超重或肥胖。如果那些提供卫生保健的人不能控制好自己的体重，又怎么能单靠营养教育来帮助减轻其他人的体重呢？

　　即使我们更了解食物本身、过大的食物支出比例和复杂的市场营销，它们仍然削弱了我们限制消费的能力。试想美国的酒精消费情况：只有那些授权机构可以把烈性酒卖给超过21岁的人，自动售货机不得出售任何酒精。但是美国现在几乎没有限制人们暴饮暴食的标准或规定。

　　十九世纪时人们还没有对饮水质量采取控制措施，传染病是死亡的主要原因。水质标准被建立起来后，死亡人数骤降。

　　类似地，如果美国人民没有生活在充满自助餐、廉价快餐、玉米糖浆饮料，还有过多含有过量脂肪、盐分和糖的食物的世界里，肥胖症、心脏病、高血压和糖尿病的发病率可能就会骤降。营养教育很有用，但我们更需要的是规章制度——比如，限制销售为迎合大众对糖类、脂肪依赖心理的食物。