Preventive Medicine: Diet and delusions about evidence

Dr. David Katz

Dr. David Katz

Our perennial pseudo-confusion about diet — and pseudo-confusion, it is — is fueled by two parallel delusions, running in opposite directions. The first is that every opinion about diet changes the facts about diet; it does not. This delusion operates as if bias, preconceived notion, having the answer before asking the question, or having something to sell — is fully commensurate with expertise and the weight of evidence.

The second, opposing delusion is that every opinion about the evidence about diet changes the standard of “sufficient evidence.” It does not. This contention harbors the view that any amount of evidence can be dismissed as inadequate or even absent by those who find the message in it inconvenient.

Perhaps, then, there is a third delusion, too — that the two delusions above can co-exist. They cannot. There is no way the assertion of a non-expert opinion at odds with, or absent any meaningful evidence can be “enough,” in a world where a vast aggregation of consistent evidence can be dismissed as inadequate or absent by those choosing to ignore it. At worst, a thinking population is obligated to pick one of these. At best, we should renounce both for the nonsense they are.

When convenient, evidence that would be inadmissible in any other field is routinely hyperbolized into dietary gospel. The current fascination with the ketogenic diet, for instance, essentially resurrects the Atkins proposition under a new rubric. It is based not on a shred of evidence that the diet is sustainable over time, or good for people if so. It is based entirely on short-term improvement in metabolic profiles of obese people with and without type 2 diabetes. But since almost anything that induces short-term weight loss improves metabolic profiles in obese people — including cocaine use, cholera, and tuberculosis — that hardly rises to the level of relevant evidence for population-wide dietary guidance.

I am not saying a ketogenic diet is akin to these overtly bad actors; we lack decisive evidence to know. I am simply saying we lack the evidence required to know that it is not, with a preponderance of related evidence offering abundant reason for concern. Proponents, however, clearly hope we will leap, on faith in magical remedies, before pausing to look at the state of our current understanding.

Our bigger problem, however, may be the delusion in the other direction: that we don’t have enough, or even any, evidence to say what diet is best. Some have made careers principally by marketing this contention. It is false.

The camp peddling the view that “there is no evidence” overlooks the considerable randomized trial evidence supporting the basic theme of an optimal diet. But RCTs are not necessarily the primary argument for a given dietary pattern. Much of the evidence about diet is written in the fate of populations of us, over lifetimes and generations, as it is for all other species.

The assertion that the only alternative to absolute certainty about every detail is abject ignorance of all fundamentals is absurd in general, as it is for diet specifically. Were it true, we would know nothing about anything. There is no science, not chemistry, not physics, not engineering —where our knowledge is remotely like perfect. Yet, it is good enough to send people to the moon and spacecraft to other planets; to split atoms; to image every nook and cranny of a living body; to transplant organs; and to beam messages such as this one through cyberspace. The prevailing alternative to knowing everything is knowing something; and at times if not often, knowing enough.

Delusions can be benign or malignant; those regarding nutrition are most certainly the latter. While the pseudo-debates over pseudo-controversies rage, and the follies of history endlessly repeat, diet has devolved into the leading cause of premature death and chronic disease in the United States. The real reasons for the carnage, under the cover of pseudo-confusion, hide in plain sight.

When you hear “there is no evidence,” look for yourself. If you readily find yourself up to your neck in citations, you need not be qualified in research methodology to know the claim of “no evidence” is false. Delusions about diet and evidence prevail, and both diet and health are the poorer for it.

My advice is simply to chew the relevant claims a bit more carefully before you swallow them.