Articles in the New England Journal of Medicine on April 30, and in the New York Times on May 19, discuss a proposal now before Congress to impose a tax on sugar-sweetened sodas in order to reduce obesity. Taxes are ordinarily intended to raise revenue, but some taxes, such as taxes on alcohol and tobacco--and on carbon emissions, should such a tax ever be passed--are designed not to raise revenue but to alter behavior, and the more they succeed in altering behavior the less revenue they generate.
Sugar-sweetened sodas are high in calories, are drunk in great quantity, and because they have little nutritional value don't substitute for other foods; they are a net addition to caloric intake. The NEJM article estimates that consumption of such sodas adds an average of 125 to 150 calories per day to the average American's diet, and cites studies that estimate that the elasticity of demand for such products is about -1, so that a 10 percent soda tax tax could be expected to reduce consumption by about 10 percent, with the result, according to the author of reducing the average person's weight by about 2 pounds a year.
I am skeptical, because the author ignores the possibility of substituting untaxed sugar-sweetened foods or beverages. People who crave sugar will find no dearth of substitutes for sugar-sweetened sodas. Moreover, most consumers of these sodas are not and never will be obese. They may well be overweight, but all that that means is that they are heavier than the "ideal" weight calculated by physicians; if they are only slightly or even moderately heavier, the consequences for health or social or professional success are apparently slight.
To the extent that a soda tax would cause substitution of equally sugared foods, it would not only have no effect on obesity; it would yield no revenue--a material consideration because supporters of the tax hope, albeit inconsistently, that it will both reduce obesity significantly and contribute significantly to financing the Administration's ambitious and very costly program of health-care reform.
There are many obese Americans, in the sense of ones who are grossly overweight (with some being morbidly obese), and we should consider whether society should be concerned with obesity if not with mere overweight. Obesity impairs health, and, in most segments of the population it diminishes social and professional success as well, and so it can be regarded as self-destructive behavior. Some of it is involuntary--there are people whose genes make it virtually impossible for them to avoid becoming obese--but most obesity could be avoided by careful diet and exercise. The obese are people who by dietary choice and preference for a sedentary style of life have traded off the costs of obesity against the costs of being thin and have decided (at least in a "revealed preference" sense--they may not have consciously chosen a style of life that predisposes them to obesity) that the costs of thinness preponderate over the benefits. And in general we do not try to prevent people from making such tradeoffs.
But there are two situations in which preventing people from choosing the style of life that maximizes their utility can be defended (provided certain assumptions are made about cost and efficacy) on economic grounds. One is where consumers are unable to evaluate a product or to act upon their evaluation; another is where a voluntary transaction imposes costs on other people which the transactors do not take into account.
The first is a significant factor in the soda market. The sellers advertise very heavily to children, who do not have the knowledge or the self-control that they would need to be able to resist such advertising. In well-ordered households, the parents regulate children's access to television and the Internet and know they should limit the children's consumption of sugar-flavored drinks and do limit it. But in many modern American households, especially but not only those in which there is only one parent, children's access to soda and soda advertising is not restricted.
The solution, though, is not a tax on sodas, as such a tax would have only a small effect. A ban on advertising would be preferable; it would probably impose only slight costs on adult consumers of such drinks, because the advertising of such drinks contains little information. It is true that such a ban would reduce new entry into the soda market and that this might lead to higher prices, but if so that would reinforce the effect on sales of the ban on advertising.
As to whether by increasing obesity the sale of sugar-flavored sodas imposes costs on other people besides the buyers, the evidence is mixed. Obese people have more health problems than the non-obese and hence higher annual medical costs; they also lose more time at work because of illness. Their poorer health increases the medical costs of other people in their insurance pools and reduces the productivity of their employers, assuming realistically that employers cannot selectively reduce the wages or health benefits of their obese employees. Cutting the other way, obese people have a reduced life expectancy, and the shorter a person's life, the less an above-average annual cost of medical care translates into an above-average total (lifetime) cost. But assuming nevertheless that the net social costs of obesity are positive, this would be a ground for arguing for taxing obesity, but such a tax would be unacceptable as well as cruel. The alternative of a soda tax would be unlikely to have much effect, for the reasons stated earlier.
Are there better ways of fighting obesity, assuming it is worth fighting? Probably not. Education would probably have very little effect, because almost all people know that being fat has bad consequences and that eating foods rich in sugar and butter and not exercising increase the likelihood of becoming obese. Obesity is concentrated in the lower middle class, which contains a high proportion of people who have very high discount rates, which prevents them from giving significant weight to the future consequences of present behavior.
Children may be ignorant about the costs of obesity and the effects on it of sugar, but because of lack of self-control and children's inability to imagine themselves as middle-aged adults, I doubt that trying to educate them in the dangers of drinking sugar-sweetened beverages would be effective.
A tax on calories, or on high-calorie foods or ingredients, would be difficult to design and administer and would impose welfare losses, without significant offsetting wealth gains, on thin people. A further problem is that fattening foods, including sugar-flavored sodas, have fallen in price over time relative to fruits and vegetables and other healthful foods, so that a tax on calories would be highly regressive.
A modest measure would be to bar the sale or other provision of sugar-flavored sodas and other fattening foods in schools, and the substitution of nutritious low-calorie school lunches for the present fare. In addition, more school time could be allotted to physical education, which in recent years has diminished in most schools. The cost of these measures would be modest and they would have some effect in reducing obesity.
译文:
征收汽水热量税以降低肥胖率——Posner
新英格兰医学期刊》及5月19日的纽约时报报道称，美国国会正在讨论一项向个人征收含糖汽水饮料的提案，旨在降低肥胖症的发病率。税收的一般目的在于增加国库收入，但某些税收，如酒税，烟草税，二氧化碳排放税等，其目的并非增加岁入，而是改变行为。这些税收成功的改变了许多人的行为，然而政府岁入却因此而变少了。
人们普遍饮用的含糖汽水的热量高，营养成分少，无法代替其他食物，只是单纯的热量摄取。《新英格兰医学周刊》上的文章称这种汽水的消费，给美国人均膳食平均增加了125-150卡路里的热量，城市研究假设该种产品的需求弹性约为-1，因此预计10%的汽水税可以降低10%的消费。作者认为，这一结果每年可以降低人均体重约2磅。
笔者对此表示怀疑，因为文章作者可能忽略了可能替代征税汽水的代替品，如未征税的甜食及饮料。嗜甜成瘾的人总能找到含糖汽水的替代品。再者，这些汽水的消费者并不一定肥胖，并且可能永远不会成为肥胖症患者。这些人也许超重，但这只意味着他们比医生认为的“理想”体重要重些；如果只是轻微超重或适度超重，很明显，这一税收的健康或社会成果，或专业成功收效甚微。
在某种程度上，汽水税会导致等糖分食品的替代，这不仅仅对肥胖毫无遏制，而且不会产生税收收入——从物质方面考虑，尽管税收支持者的观点不尽相同，但都认为这一举动将大幅降低肥胖症，并且对政府宏伟而昂贵的医疗体制改革提供巨大的财力支持。
在美国，有许多胖人。就那些过于肥胖的人而言（其中有些肥胖症患者），我们需要考虑整个社会是否需要关注除了单纯的超重之外的肥胖人群。肥胖有害健康，在多数社会群体中，肥胖对社交及专业的成功有负面影响，因此可以被认为是一种自我破坏的行为。有些人不可避免的发胖——基因使然。但多数肥胖是可以通过细心的饮食和足够的锻炼来避免的。人们选择饮食习惯及极少量运动的生活方式（至少是“明显的喜爱”——并非有意选择一种更容易使其发福的生活方式），付出的代价是渐渐发福而非日益清减，认为清瘦的代价多余益处，从而导致了这些人成为胖子。一般我们并不阻止这些人以牺牲苗条来换取肥胖的交易。
但在经济背景下，有两种情况，能够阻止人们选择最大化他们的用途并可以坚持的生活方式。一种是消费者无法评估一种产品的价值或根据价值采取行动；另一种是当自愿交易将成本强加于交易人不相关的其他人时。
第一种情况是汽水市场的一个重要因素。销售者对孩童大肆进行广告宣传，孩子的自制力差，无法抵制这种广告的诱惑。在秩序良好的家庭，家长限制孩子接触电视机和网络的时间，并且意识到应该限制孩子对含糖饮料的消费并且付之行动。但大多数现代美国家庭，特别是单亲家庭，孩子接触汽水及汽水广告没有一定的限制。
这一解决方法，并非汽水税，因为这一税收收效甚微。更好的方法是限制广告。对于成年消费者而言，这可能只增加一小部分成本，因为这种饮料的广告信息量极少。毫无疑问，这一限制将缩小打开饮料市场的通路，导致价格升高，但可以巩固禁止销售饮料广告的影响。
对于是否增加肥胖，对汽水征收除购买者之外的人的税，证据是各种各样的。肥胖者比正常人有更多的健康问题，因此每年花费更多的医疗支出，同时因为疾病，丢失了工作时间。他们糟糕的健康状况增加了同保险集团其他人的医疗支出，降低了雇佣者的生产效率，现实的假设，雇佣者不能选择性的降低肥胖者的工资或医疗福利。另一方面，肥胖者寿命较短。一个人的寿命越短，所消费的年均医疗费用就越低。尽管假设肥胖的社会净支出为正，这将成为征收肥胖税的背景，但肥胖税既不可接受，又无情。选择汽水税就不会有这样的影响，正如之前所述的理由。
假设对抗有价值，有没有其他对抗肥胖的方法呢？可能没有。教育的影响可能相当小，因为几乎所有人都知道发胖的后果，食用含糖量高的食品及黄油，不运动都会导致肥胖。肥胖多发于中下阶级，包括很大比例高折扣率的人群，这使他们不能因为现在的行为而对未来的后果增加重量。
孩子对肥胖的后果一无所知，因为他们自制力差，并且无法想象自己成为中年人。我怀疑对其进行教育，告诉他们和含糖饮料的后果，这种方法并无效果。
对卡路里，或高卡食物、佐料收税，这一做法设计起来困难，实施起来更困难，导致福利丢失，却对瘦人收入补偿甚微。更进一步的问题是，导致肥胖的食物，包括含糖饮料，长久以来，相比水果蔬菜及其他健康食品，降价幅度更大，因此对热量收税将大幅的降低。
妥当的方法是，阻碍含糖饮料及其他导致肥胖的食物在校园的销售或提供，使用营养丰富，含热量低的学校午餐替代当前的伙食。此外，孩子在学校的运动时间应该更多，而近几年多数学校降低了学生的活动时间。这些措施的成本相对合适，并将对降低肥胖产生一定效果。