By Cen Rong Translation： Li Li

The Economist’s Weight-Loss Strategy

By Cen Rong Translation： Li Li

A study on people’s waistlines in the U.S. found that our f o o d i n t a k e h a s increased since the 1970s, while the energy we consume every day maintained at a steady level.Daily calorie intake increases by 300 kilojoules every decade.Obesity has now become a major problem that troubles people’s lives.

Economists found that bigger plates, bowls, and even pantries increase our food intake.

In a test, researchers put popcorn, which had been stored for 14 days in buckets of various sizes and then gave them to the audience at a cinema. It was found that the audience who took the bigger bucket ate 38%more expired popcorn than other people. It tells us that people decide to stop eating according to external information (i.e.my plate is empty) rather than internal information (I am full).

In another test, scientists randomly gave 10 weightloss strategies to participants and found two strategies most effective: participants who used smaller plates (dia<25cm) to eat lost an average of 0.9kg within one month; experimenters who were not allowed to watch TV while eating lost 0.7kg on average in one month.

Brian Wansink, director of the Cornell University Food and Brand Lab, found that people consumed 28%～55% more food while they watch sad movies;people eat less with softer lighting and soft jazz ballads playing; lower contrast between the color of the plate and color of the food makes people consume 22%～32% more food.

Apart from appetite control,keeping fit is another key to losing weight. Some economists tried to help people to keep exercising by providing incentives.In an experiment designed by Uri Gneezy, professor of economics from University of California, a group of students were separated into two groups: experimental group and control group. The experimental group was promised an additional$100 for attending the gym at least eight times over four weeks, while there was no incentive for the control group.

美国一项针对腰围的研究发现：从1970年左右开始，我们身体每天的能耗就基本维持在一个稳定的水平，但人们的食量开始增长，每过十年，我们的日均能量摄入量增长300千焦，于是肥胖成为一个困扰现代人的重大问题。

经济学家们发现，更大的盘子、碗甚至是食品柜，都会增大我们的食量。

在一项实验中，研究者把一些存放14天的爆米花，装在不同规格的桶中分给电影观众，结果拿大桶爆米花的观众，比其他人多吃下38%的过期爆米花。这说明人们往往根据外部信息（我的盘子空了），而非内部信息（我饱了）停止进食。

在另一项实验中，他们把10条减肥策略随机分配给实验参与者，最终他们发现最成功的两条减肥策略：坚持用小盘子（直径小于25厘米）进食的参与者，一个月内平均减掉0.9公斤；吃饭时禁止看电视的实验者，一个月内平均减掉0.7公斤。

康奈尔大学食物与品牌实验室主任布莱恩·万辛克发现：看悲伤的电影会让你多吃28%至55%的东西；餐厅中柔和的灯光和动听的爵士乐会让你吃得更少；所持餐盘的颜色与盘中食物的颜色色差较小，会让人多吃22%至32%的食物。

除了控制食欲，减肥的另一个关键是健身。经济学家试图通过激励机制让人们保持锻炼。美国加州大学经济学教授尤里·格尼茨等人做过一个实验，他们招募一些学生，把他们分为两组，一组是“实验组”，另一组是“对照组”，如果实验组的学生一个月内去健身中心健身的次数达到8次，他们就奖励这些学生100美元，而对照组则不提供奖励。

正如经济学家所预料的，实验组的学生大都乖乖去健身。然而，经济学家们想弄清激励机制能否有助于长期习惯的养成，一个月过去之后，不再提供奖励，情况又会怎样？

结果令人振奋，即使停止奖励，实验组学生去健身的频率仍然是对照组的两倍，这些简单的激励机制帮助学生克服惰性，形成定期运动的习惯，同时也学会怎样挤出时间运动。

美国广播公司的黄金段节目《生活：博弈》，试图通过参与者的羞耻感来起到减肥的作用。体态超胖的参与者必须同意只穿一件比基尼来拍照，接下来的两个月，对所有未能成功减重15磅的人，都要把他的照片在国家电视台公开，并登在该节目的网站上。

Just as the economist predicted,students in the experimental group went to the gym as required. However,the economist wanted to know whether incentives would help people to foster a habit. What would happen if there was no incentive after one month?

The results were encouraging.Students in the experimental group attended the gym twice as often as those in the control group. This simple incentive helped students overcome their laziness and form a habit of regular exercise. They also learned to squeeze in time for exercise.

On ABC Primetime’s Game Theory,they tried to help participants lose weight by making them feel ashamed.Overweight participants agreed to take a photo in a bikini. For those who failed to lose more than 15 pounds over the next two months, the photos would be seen on the TV and the Internet.

The economist said this is the behavior of strategy—they were betting with their future self. You want the future self to eat less and exercise more, while the future self wants to eat ice cream and watch movies. It is the future self that wins most of the time. People always start to take action when it’s too late.

The only way to solve this problem is to change the incentive for the future self so as to change your behavior.The temptation of overeating or overspending is still there, but the possibility of being exposed to an embarrassing moment shuts off the temptation. Avoiding such catastrophic exposure becomes a powerful incentive.

In the end, every participant in the program lost more than 15 pounds except one person who almost did.

Dean Karlan, an economist from Yale University, aspired to lose weight. He signed an agreement with a friend who had the same wish. It was stated that whoever was over 175 pounds would pay the other $1000 for every pound over.

Tyler Cowen, professor of economics at George Mason University, had another suggestion: post a bond with your friend, your spouse, and your exercise partner. Write a check in advance. You lose the money if you don’t exercise according to a prearranged plan with well-defined quantitative goals.

However, Taylor also admitted that too many external incentives could reduce internal motivation. ◆

经济学家把这种行为归为“策略行动”，也就是说，他们在和未来的自己博弈，今天的自己想让未来的自己节食和运动，而未来的自己想吃雪糕和看电影。但大多数时候总是未来的自己获胜，人们总是在最后才行动，那可悔之晚矣。

解决这一问题唯一的办法是，改变对未来自己的激励，从而改变自己的行为。过度饮食或过度花费的诱惑仍然存在，但令人羞耻的曝光的可能性阻断这种诱惑。想避免这种灾难性的曝光，就成了一种强有力的激励。

最后所有的减肥节目参与者都减掉15磅以上，除了 一个人，那个人差点也成功了。

耶鲁大学经济学家迪安·卡尔兰渴望减肥，他与另一位渴望减肥的朋友签订一个合同，如果谁的体重超过175磅，超重的那个人就要按照每磅1000美元的标准付给对方。

美国乔治·梅森大学的经济学教授泰勒·考文也建议说：你可以向朋友、配偶、运动伙伴等“邮寄保证金”，提前写好支票，如果自己不按照目标定量做减肥健身，就得把这笔钱送给对方。

不过泰勒也承认，太多的外部激励能够减少内部动机。◆

经济学家减肥策略

文/岑嵘 译/李莉

(From Hangzhou Daily, May 22,2017)

（摘自《杭州日报》2017年5月22日）