Fat and spinach

There’s an old joke — I’ve seen it attributed to Clarence Darrow, but I have no confidence in this attribution — that goes

I don’t like spinach, and I’m glad I don’t, because if I liked it I’d eat it.

I thought of this in reflecting on the lessons of Nina Teicholz’s book Big Fat Surprise, about the sorry history of public health recommendations about dietary fat, mainly in the US. This will surely go down as one of the most embarrassing disasters in public health history, so Teicholz’s efforts to uncover how a supposedly self-correcting process was able to go so badly wrong holds important lessons for all of us who care about either science or public policy. (It’s sort of The Innocence Project, with observational studies in place of eyewitness misidentification.)

Of course, scientists invariably design studies and interpret their results in terms of their best current theories, and this can allow them to accumulate quite a few “anomalies” and “paradoxes” before they are willing to change course. On top of that comes the usual helping of self-love and intellectual rigidity, exacerbated when charismatic figures have identified themselves and their reputations with a particular model. The well-documented inadequacies of the prevailing custom of null-hypothesis statistical testing (NHST) — with the unfortunate terminological confusion between “not significant” (meaning that the hypothesis was not effectively supported by the data) and “insignificant” (not worth considering) — led to studies that strongly contradicted the “saturated fat causes heart disease” dogma being dismissed or buried in appendices or obscure journals, rejected even by their own authors.

(The English-language confusion between “fat” (the macronutrient) and “fat” (overweight) seems to have also played an important role in stoking confusion.)

But there is a much more potent poison paralysing the scientific process when public health and self-righteousness intersect with scientific theorising. Teicholz shows how research intended to challenge the purported link between fat and heart disease was attacked and suppressed, with arguments that it would be unethical to put study subjects on a high-fat diet (since it is known to be harmful), or because the results might confuse the public and undermine the important goal of getting people to follow the official (low-fat) dietary guidelines. In other words, if we find evidence that dietary fat is harmless, that would be terrible, because then people would eat more fat.