Our perennial pseudo-confusion about diet- and pseudo-confusion, it is- is actually 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. If either is right, the other cannot be. There is no way that 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 them both for the nonsense they are.
I have addressed the matter of dietary pattern, the fundamentals consistent with the basic care and good feeding of Homo sapiens, many times before- so let’s focus here on those delusions of evidence.
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 the 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 the 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 actual 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 very contention.
It is false.
The camp peddling the view that “there is no evidence” is in some ways very analogous to their counterparts who do the same regarding evolution. The evidence for evolution by natural selection is, with apologies to those who find this truth inconvenient, incontrovertible.
The fossil record is compelling- just as the randomized trial (RCT) evidence supporting the basic theme of an optimal diet is compelling (see, for instance, this one, and this one, and this one, and this one, and this one, and this one, and this one, to list a very few). But just as RCTs are not necessarily the primary argument for a given dietary pattern, fossils are not the primary argument for evolution. Rather, the evolutionary evidence that truly matters is written in the language of molecular genetics, where there is practically a manual, for those literate to it, of how speciation occurred. Much of the corresponding evidence about diet is written in the fate of populations of us, over lifetimes and generations- just as it is for all other species.
The assertion about evolution that “there is no evidence,” or “there is no proof,” comes from those not literate to, or refusing to read, the bountiful proof in hand. It also comes from those who seem inclined to propound that the only alternative to absolute certainty about every detail is abject ignorance of all fundamentals. So, too, for diet.
If that contention were 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.
Those claiming that knowledge is all or nothing are generally either deluded themselves, or predatory- seeking to foster a gullibility they intend to exploit.
Imagine for a moment that this delusion were true; that want of RCTs, or simply not knowing everything- means knowing nothing. A short list of the things we could not know under those conditions includes: that cigarettes cause lung cancer or emphysema; that breathing every hour is necessary for survival; that water is better than gasoline for putting out fire; that working for organized crime increases the risk of death by violence; that parachutes improve outcomes when jumping out of planes. Expand the list yourself as the spirit moves you.
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 evolved 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.
This is the work of merchants of doubt, whether predatory or delusional, and in the company of their other such abuses. Just such feigned doubt was used to shield the tobacco industry from its rightful indictment for years, at a cost measured in lives. It is used to perpetrate the peddling of guns, which is all about money whatever the pretended Constitutional cover. It is used to justify the climate change procrastination and prevarication that are melting our ice, and sure to cook our goose.
When you hear assertions about diet, look for their basis in something resembling science; either with a trip to the library and the advantage of some expert help, or simply at the tip of your typing fingers. Be sure to look both ways, for sources both for, and against. If the claims seem at odds with, or out of proportion to, the kinds of evidence you find- they almost certainly are. Step away from your credit card.
Similarly, 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.
Some contend that saturated fat is the worst of nutrition, while others contend it is sugar. I contend it is- forgive me- stupidity: a fatuous processing of food for thought, and a failure to differentiate fact from personal preference, or profiteering fantasy. So it is that dietary delusions prevail, and both diet and health are the poorer for it.
My advice is simply to chew the relevant information a bit more carefully before you swallow it.
David L. Katz, MD, MPH, FACPM, FACP, FACLM, is the Founding Director (1998) of Yale University’s Yale-Griffin Prevention Research Center, and current President of the American College of Lifestyle Medicine. He has published roughly 200 scientific articles and textbook chapters, and 15 books to date, including multiple editions of leading textbooks in both preventive medicine, and nutrition. He has made important contributions in the areas of lifestyle interventions for health promotion; nutrient profiling; behavior modification; holistic care; and evidence-based medicine. David earned his BA degree from Dartmouth College (1984); his MD from the Albert Einstein College of Medicine (1988); and his MPH from the Yale University School of Public Health (1993). He completed sequential residency training in Internal Medicine, and Preventive Medicine/Public Health. He is a two-time diplomate of the American Board of Internal Medicine, and a board-certified specialist in Preventive Medicine/Public Health. He has received two Honorary Doctorates.