The True Science of Spinach and What the Popeye Mythology Teaches Us about How Error Spreads

During my teenage years, given my athleticism, my insatiable appetite for spinach, and my last name, friends were quick to latch onto the stuff of pop-culture legend and nickname me Popeye. But it turns out that besides perpetrating the crime of the too-obvious-for-its-own-good pun, they were also perpetuating one of history’s strangest and most egregious scientific errors.

In The Half-life of Facts: Why Everything We Know Has an Expiration Date (public library) — the same fascinating volume that explored how Gutenberg’s press embodied combinatorial creativity and the predictable patterns of how knowledge grows — Samuel Arbesman illustrates how error spreads by debunking the Popeye mythology through the curious story of the scientific error that precipitated the misconception.

Popeye, with his odd accent and improbable forearms, used spinach to great effect, a sort of anti-Kryptonite. It gave him his strength, and perhaps his distinctive speaking style. But why did Popeye eat so much spinach? What was the reason for his obsession with such a strange food? The truth begins more than fifty years earlier. Back in 1870, Erich von Wolf, a German chemist, examined the amount of iron within spinach, among many other green vegetables. In recording his findings, von Wolf accidentally misplaced a decimal point when transcribing data from his notebook, changing the iron content in spinach by an order of magnitude. While there are actually only 3.5 milligrams of iron in a 100-gram serving of spinach, the accepted fact became 35 milligrams. To put this in perspective, if the calculation were correct each 100-gram serving would be like eating a small piece of a paper clip. Once this incorrect number was printed, spinach’s nutritional value became legendary. So when Popeye was created, studio executives recommended he eat spinach for his strength, due to its vaunted health properties. Apparently Popeye helped increase American consumption of spinach by a third! This error was eventually corrected in 1937, when someone rechecked the numbers. But the damage had been done. It spread and spread, and only recently has gone by the wayside, no doubt helped by Popeye’s relative obscurity today. But the error was so widespread that the British Medical Journal published an article discussing this spinach incident in 1981, trying its best to finally debunk the issue.

Arbesman uses the Popeye story as an allegory of admonition against the all-too-human ego and our chronic propensity for shortcuts, the combination of which makes us too lazy to look closer and too afraid to admit we’ve been blind and wrong:

Ultimately, the reason these errors spread is because it’s a lot easier to spread the first thing you find, or the fact that sounds correct, than to delve deeply into the literature in search of the correct fact.

But perhaps the most fitting reflection on what the Popeye story teaches us can be found in Dorion Sagan’s fantastic meditation on why science and philosophy need each other, in which he observes:

It is the spirit of questioning, of curiosity, of critical inquiry combined with fact-checking. It is the spirit of being able to admit you’re wrong, of appealing to data, not authority, which does not like to admit it is wrong.

Complement The Half-life of Facts with Galileo on critical thinking, Michael Faraday on how to cure our propensity for self-deception, and Carl Sagan’s timeless Baloney Detection Kit.

Public domain photograph via State Library of New South Wales