Causation or correlation?
Keys and company found that men in Italy and Greece had lower cholesterol, seemed to drop dead less often, and said they ate less red meat than their American counterparts. Keys extrapolated his anti-meat message from there, and his crusade landed him on the cover of TIME.
Despite the great publicity, Keys had found an interesting fact pattern but nothing more. Even amateur scientists know that correlation is not causation.
Men in Italy and Greece had less coronary heart disease than American men -- they also had less use for the English language. Doesn’t mean speaking English causes heart disease. In most scientific experiments, observational studies lead to hypotheses, along the lines of “meat may cause coronary heart disease,” and then the real work begins. To test a hypothesis, researchers design a randomized, controlled study and complete it. And this is where the advice on meat falters.