You are absolutely right. That professor must have been "old school". Today, the value of null-results is better appreciated, though not to the extent it should. And Ancel Keys and his 7-countries study is often portrayed as the poster child, but that's not entirely justified. . It is the Ancel Keys bashing that has been creeping into virtually all posts and articles that discuss the “flaws” of the 7-countries study.

Typically the accusation of cherry picking is underscored with a graph that Keys produced to show the strong association between dietary fat intake and mortality in 6 countries in his paper “Atherosclerosis: a problem in newer public health”. The problem is that this paper, published in 1953 in the Journal of Mount Sinai Hospital, PREDATES the start of the 7-countries study. In the early 1950s Keys had been limited in the selection of countries, simply because for 16 countries of his interest only those 6 had comparable diet and mortality statistics available. It was, after all, the aftermath of WW 2. Keys had received immediate criticism from two statisticians, Yerushalmy and Hilleboe, in their 1957 paper “Fat in the diet and mortality from heart disease; a methodologic note”.

So, Keys’ association-suggests-causation argument was already under attack before the 7-countries study delivered any results. My point is, the contemporary alphas in public health had enough evidence and arguments at hand to tread more cautiously than they did when publishing their dietary guidelines for the next few decades. In so far, making Keys the scapegoat, is in my eyes, a deflection of blame and an exercise in self-preservation of those public health policy makers who could and should have known better. Which is why I’m always sceptical about anything that comes out from guideline committees and their inscrutable consensus finding processes