Diet and Fat: A Severe Case of Mistaken Consensus

By John Tierny

New York Times Article: October 9, 2007

In class we have been discussing this notion of information cascades and how easily we can be influence by the choice of others. One interesting figure that was mentioned in the article points to research done by a group of economists. If, say, 60 percent of a group’s members have been given information pointing them to the right answer (while the rest have information pointing to the wrong answer), there is still about a one-in-three chance that the group will cascade to a mistaken consensus. So how does this relate to the medicine field? “Cascades are especially common in medicine as doctors take their cues from others, leading them to over-diagnose some faddish ailments and over-prescribe certain treatments. Unable to keep up with the volume of research, doctors look for guidance from an expert — or at least someone who sounds confident.

What this article describes is how information cascade brought about the idea that low-fat diets will reduce heart disease. The argument is that there has been no scientific proof that the former is true and as a result of this recommended diet, people have been switching to diets rich with carbohydrates, which is believed to obesity and disease. So if this diet hasn’t been scientifically been proven to be effective, how does it have the endorsement of “92 percent of the world’s leading doctors.?”

It can all be explained with the idea of information cascade. It all goes back to Ancel Keys, a prominent diet researcher a half-century ago. He became convinced in the 1950s that Americans were suffering from a new epidemic of heart disease because they were eating more fat than their ancestors. However, upon making this argument, two glaring problems were made apparent. First, according to the best estimate possible, ancient hunter-gatherers ate just as high or higher than the diets we practice today. Second, there wasn’t really a new epidemic of heart disease. Yes, more cases were being reported, but not because people were in worse health. It was mainly because they were living longer and were more likely to see a doctor who diagnosed the symptoms.

In 1957, the American Heart Association declared that dietary fat did not correlate directly with heart disease, however, three years later, the association changed position, largely because Dr. Keys was on the committee issuing the report. This report led to an acceleration of the cascade in the 70s when Senator George McGovern issued a report advising Americans to lower their risk of heart disease by eating less fatty foods. Again, this report wasn’t based on hard scientific data, instead, much of it was due to the cascade effect. This report then led to the creation of the food pyramid in the 1980s. So basically, the food pyramid that we all learned about in elementary school was largely due to this phenomenon of information cascade.

In an effort to help control this cascade effect, a group of scientists at the National Academy of Sciences released a report stating that there still wasn’t enough evidence to recommend a low fat diet to all Americans. However, they were promptly excoriated publicly for denying the danger that had already been proclaimed by many reliable sources.

This is a matter of such enormous social, economic and medical importance that it must be evaluated with our eyes completely open. Thus I would hate to see this issue settled by a cascade. Tests continue to refute this notion of non-fat diets, although it makes sense, its not one hundred percent valid. Even though it’s an interesting topic, it’s even more interesting how information cascades plays a role in even in subjects like this.