http://www.nytimes.com/2007/10/09/science/09tier.html

http://tierneylab.blogs.nytimes.com/2007/10/09/how-the-low-fat-low-fact-cascade-just-keeps-rolling-along/

The article that I’ve chosen for this post (first link) is about how the medical world was duped into the cascading idea that a low-fat diet would lower the risk of heart disease. John Tierney, a science columnist for The New York Times, cites Gary Taubes’ book, Good Calories, Bad Calories to explain the steps that led to the commonly accepted idea, which has never been proven, and yet was endorsed by numerous health organizations, officials and doctors all the way up to the Surgeon General in 1988. It started with the confident voice of Ancel Keys, a prominent diet researcher of his time, who became convince in the 1950s that an increase in the number of cases of hearth disease in America was correlated with an increase in the amount of fat in Americans’ diets. He supported his theory with a weak study of a few countries’ populations (weak because, as Tierney points out, if he had used more countries – for which data was available – he would not have found such a correlation). Then, in 1960, Keys and an ally were on an American Heart Association committee that issued a report asserting that a low-fat diet would lower the risk of heart disease. This report made the theory popular wisdom, and in the 1970s, a senate committee, led by Senator George McGovern, issued another report warning Americans to lower their fat intake. This senate report was only supported with input from one nutritionist, Mark Hegsted, who, in turn, was hired by an assistant agriculture secretary to draw up a set of national dietary guidelines for the Department of Agriculture. In multiple instances, doubters emerged, but there were too many supporters of the theory for them to be able to convince anyone of their case. Ultimately, the idea became a commonly held belief, and according to Senator McGovern, “92% of the world’s leading doctors” endorsed it; however, as Dr. Edward H. Ahrens Jr. responded, many of those doctors were relying on second hand knowledge.

This phenomenon is a perfect example of information cascade, which we discussed in class. The author of the article, John Tierney, subsequently made a blog post (second link), which essentially explains what an information cascade is, and how it is that dietary research so often gains enormous support and tons of followers, only to later be contradicted and/or proven ineffective. To support his analysis that large groups often reach a ‘consensus’ without everyone fully understanding the issue, Tierney cites Brown University economist Dr. Ivo Welch. Welch explains that it all comes down to the fact that many choices are binary. In the case of diets, someone can endorse it or not, but they cannot partially endorse it. Therefore, after a few people have chosen to endorse a diet, it is very easy for many more that follow to believe that the diet is a good idea because they assume the endorsers cannot all be wrong. Welch explains that sometimes a cascade can change direction, for instance when a few people introduce a new idea that is opposite of the commonly held belief, and subsequently more and more people switch their beliefs, he also notes that this can occur for either the right or wrong choices. This explanation by Tierney and Welch ties in precisely to what we have learned in class and in the text about information cascades.