Knowing Well, Being Well: well-being born of understanding: Dietary Research Done Right: From Je Ne Sais Quoi to Sine Qua Non

Introduction Fascination with the idea that some diet is ‘‘best’’ is, literally, perennial. Popular interest in a parade of food and ingredients as contenders for silver bullet or scapegoat is seemingly as persistent. These 2 fixations of popular culture pose a singular challenge to nutritional epidemiology. For there to be a rebuttal, predicated on evidence, to marketing hype and misdirected hope, the relevant evidence must be generated. The charge has been levied, repeatedly and at volume that nutritional epidemiology is flawed in its methods for pursuing reliable evidence and fundamental truths. The result of such assaults, aided and abetted by the hospitality peer-reviewed journals routinely accord them, is a state of persistent pseudo-confusion about diet that obviates the conversion of what we have long known into what we do to good public health effect. The charge of deficiencies in nutritional epidemiology is true at least in part: there is much yet to learn. That, of course, is true in every field of human inquiry. The proposed remedies, however-notably, the contended exclusive need for ever more randomized controlled trials, and the unfailing advantage in ever larger cohorts—are not merely flawed, but actually corrosive to understanding. Randomized controlled trials do not pertain to every important question in nutritional epidemiology, including the most fundamental of all: what way of eating produces the greatest combination of vitality and longevity? To generate this answer directly, a RCT would need to span the lifetime of its participants. Of even more concern, RCTs can all too readily be designed to deliver the ‘‘winner’’ favored at the start, and then sanctify that conclusion under the halo of ‘‘robust methods. ’’ While critics rightly note inconsistent findings about the isolated health effects of given foods or nutrients, this is often because the dietary context, or population, have varied as well. What a food does or doesn’t do owes much to the company it keeps, and that is all too easily manipulated. To feed the popular fascination in competing diets, the ‘‘what’’ of dietary patterns is at times conflated with the ‘‘how. ’’ Various means of moderating daily energy (calorie) intake, or fostering satiety, are fully compatible with diverse diets of far-ranging composition. These ‘‘how to’’ elements of eating well and/or salutary energy balance are often pitted against ‘‘what to’’ dietary patterns, in pursuit of a winner. The answer in all such cases is a non sequitur, because the question is altogether vapid. The French expression ‘‘je ne sais quoi’’ has been adopted into the English vernacular to mean: ‘‘a certain something. ’’ The literal translation, however, of this slightly grammatically handicapped French expression is: ‘‘I don’t know what. ’’ When the effects of food or ingredient A on health outcomes are being tested, but the addition of that food causes reductions in the intake of food B-there is more than one variable in motion. Attribution of outcomes to just one of them becomes impossible because we, literally, ‘‘don’t know what’’ the causal factor is-even if our methods wear the imprimatur of a RCT. Similarly, when Diet A and Diet B are