Blog | Friday, February 9, 2018

Best diets of 2018 are deja vu all over again


In what has become a seasonal rite nearly as reliable as the solstice, US News and World Report has issued its rankings of best diets to coincide with the turn of the calendar. Once again, I was privileged to serve as one of the judges.

Our methods were much as they have been in years past. Editors at USNWR choose the diets for us to score, based largely on their popularity and prevalence. The intent is not to make this a diet popularity contest, per se, but rather to acknowledge that the diets of greatest interest to readers are the ones most people are on, have tried, or are considering.

For each diet, each of us receives a generally quite excellent summary of the principles and relevant scientific evidence. We are invited, and encouraged, to draw from our own knowledge of the related evidence, and/or to review the literature as warranted to inform our judgments.

Those judgments are then expressed numerically, using a 5-point ordinal scale, across a range of categories pertaining to soundness, safety, effectiveness for various health conditions, and ease of maintenance. Each of us 25 judges fills out our score sheets independently, and anonymously; none of us knows what others have decided, and we do not confer with one another. Unlike a jury, this process involves 25 fully independent verdicts.

The numerical scores are aggregated and averaged by USNWR, and the rankings are generated accordingly. As that methodology suggests, each judge exerts only a small (roughly 4%) influence on the outcome, and the results can at times vary markedly from what any one of us prefers or believes. In my view, USNWR does an admirable job of recruiting judges with diverse expertise, and thus producing an average conclusion born of hybrid vigor.

For this year's rankings, more diets were added to the roster, bringing the total up to 40. The long-popular diets from years past were retained, with the additions of those diets that have currently captured the public imagination, for whatever reason. Notable among those this year was the ketogenic diet.

The results, from my perspective, validate the proposition that the fundamental truths about diet are very stable over time, quite simple, abundantly clear to all genuine experts, and tend to enjoy the endorsement of multidisciplinary consensus on the basis of both science, and sense. Accordingly, all of the top scoring diets emphasize the principles none has ever summarized better than Michael Pollan: real food, not too much, mostly plants. The overall “winners,” the DASH diet developed by the NIH originally to combat hypertension; and the Mediterranean diet, are all about wholesome foods, mostly plants, in balanced and sensible combinations. These diets, followed by the “flexitarian” diet, won top honors because they are sound, well studied, and generally considered relatively easy to adopt and sustain.

What of the ketogenic diet, currently basking in its 15 minutes of public adulation? It ranked last.

While for the most part the results line up with both science and sense, there are some important limitations to both what we might call “the trial” of diets, and the verdicts. The experts are, of course, people just like everybody else, and we, too, may be influenced by what is currently in vogue. The Mediterranean diet is no better for people this year than last, and is unlikely to be better for health than, say, a traditional Okinawan diet; but it has been much in the news, and in the scientific literature of late. I suspect concentrated attention by the public may influence the inclinations of the judges.

I think the imprimatur of a diet may do the same. The DASH diet has always done well in these rankings both because it is a very sensible diet, and also because it is a product of the NIH, with all of the resources and legitimacy attached.

Finally, I suspect there is a bit of neophilia, love of the new, at work here, too. The Ornish diet, for instance, is just as good for heart disease reversal this year as last, yet moved down from the number 1 to the number 2 spot for heart health, for no particular reason other than the current preoccupation with the DASH and Mediterranean diets.

As for the “trial,” its limitations in my view are much as they have always been. First, we judges don't get to decide what diets to score. Second, some very important parameters are omitted from the scoring. I have long maintained, for instance, that people “diet” alone, but live it together as families, and for that very reason, “dieting” that is not family-friendly should just die! We should be focused on eating well in a sustainable way with the strength of unity at the level of family and household. The USNWR score sheets do not ask about suitability for all members of a family, children and adults alike, and I think they should.

Another reasonable quibble with our methods is the notion that one diet is best for diabetes, another best for heart health, another best for weight loss. In my view, that's not true, and thank goodness! Most people with type 2 diabetes are overweight, and so need a dietary pattern that can address diabetes and weight alike. Diabetes markedly increases risk of cardiovascular disease, so they need a diet that is ideal for heart health, too. What is such a person to do- go on three diets simultaneously? Of course not. A diet that is ideal for health is, in general, ideal for all of health. Condition-specific approaches to diet need not involve more than delicate, fine tuning of a general approach that is just plain good for all parts of all of us.

Perhaps the single greatest limitation to this exercise is the implication that fundamental conclusions about diet and health have any reason to change with the turn of the calendar; they do not. The basic truths about diet and health are fortified and refined by modern science, of course, but have stood the test of time and are stable not just year to year, but generation to generation. Diets of wholesome, whole foods, mostly (or exclusively) plants in sensible and balanced combinations are best this year; were best last year; and will be best next year.

May you diet, or better yet, live it, this year, accordingly.