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that dietary fat was at the center of the epidemic, and to
illustrate this, he drew up a graph from national data that
depicted a perfect correlation between total calories
consumed from fat and death rates from heart disease. Six
countries were included.
Ancel Keys is often credited for having set off the
domino effect that sculpted nutrition policy for the next
sixty years, but his argument was built on data that was
biased and ultimately misconstrued. His graph highlighted a
correlation between two variables that had been cherry-
picked amid the endless sea of variables that one encounters
when studying things like diet across the population scale.
But correlations cannot prove causation; they can only show
relationships that are used to guide further study. In this
case, however, the causal presumption was made, turning
Keys into a national hero and landing him on the cover of
Time magazine in 1961.
As it was taking a foothold in the national conversation,
there was a growing chorus of voices within the scientific
community who saw through Keys’s work. Many thought
that the validity of Keys’s correlation itself was
questionable: he omitted data that was available from sixteen
other countries that, if included, would have shown no such
correlation. For example, there was no epidemic of heart
disease in France, a country whose citizens love their cheese
and butter—the so-called French paradox. Others doubted
that there was any link between fat consumption and heart
disease at all.
John Yudkin, founding professor of the Department of
Nutrition at Queen Elizabeth College in London, was one of