Avoiding fat has almost become a fad. But fat isn't necessarily bad, argues Gary Taubes in his "Good Calories, Bad Calories," published in the US recently.
The notion that fatty foods shorten your life began as a hypothesis based on dubious assumptions and data and attempts to confirm it have failed time and again, Taubes, a correspondent for the Science magazine, says.
The popular attitude to fats could be attributed to the cascade phenomenon.
Cascades are especially common in medicine as doctors take their cues from others, leading them to overdiagnose some faddish ailments (called bandwagon diseases) and overprescribe certain treatments (like the tonsillectomies once popular for children). Unable to keep up with the volume of research, doctors look for guidance from an expert — or at least someone who sounds confident.
In the case of fatty foods, that confident voice belonged to Ancel Keys, a prominent diet researcher a half-century ago (the K-rations in World War II were said to be named after him). 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.
There were two glaring problems with this theory. First, it wasn't clear that traditional diets were especially lean. Nineteenth-century Americans consumed huge amounts of meat; the percentage of fat in the diet of ancient hunter-gatherers, according to the best estimate today, was as high or higher than the ratio in the modern Western diet.
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.
To bolster his theory, Dr. Keys in 1953 compared diets and heart disease rates in the United States, Japan and four other countries. Sure enough, more fat correlated with more disease (America topped the list). But critics at the time noted that if Dr. Keys had analyzed all 22 countries for which data were available, he would not have found a correlation.
And, as Taubes notes, no one would have puzzled over the so-called French Paradox of foie-gras connoisseurs with healthy hearts.
The evidence that dietary fat correlates with heart disease "does not stand up to critical examination," the American Heart Association concluded in 1957.
But three years later the association changed position — not because of new data, but because Dr. Keys and an ally were on the committee issuing the new report. It asserted that "the best scientific evidence of the time" warranted a lower-fat diet for people at high risk of heart disease.
And then in the 1970s a committee led by Senator George McGovern issued a report advising Americans to lower their risk of heart disease by eating less fat. The US Department of Agriculture followed suit in 1980.
There still wasn't good evidence to warrant recommending a low-fat diet for all Americans, the National Academy of Sciences noted in a report shortly after the USDA guidelines were issued.
But the report's authors were promptly excoriated on Capitol Hill and in the news media for denying a danger that had already been proclaimed by the American Heart Association, the McGovern committee and the U.S.D.A.
The Academy scientists, despite their impressive credentials, were accused of bias because some of them had done research financed by the food industry. And so the informational cascade morphed into what the economist Timur Kuran calls a reputational cascade, in which it becomes a career risk for dissidents to question the popular wisdom.
Taubes argues that the low-fat recommendations, besides being unjustified, may well have harmed Americans by encouraging them to switch to carbohydrates, which he believes cause obesity and disease. He acknowledges that that hypothesis is unproved, and that the low-carb diet fad could turn out to be another mistaken cascade. The problem, he says, is that the low-carb hypothesis hasn't been seriously studied because it couldn't be reconciled with the "low-fat dogma."
And Taubes wants an impartial re-examination of all the issues involved.