PURE diet nonsense

A massive diet study called PURE, just published in The Lancet, seemed to receive only slightly less media attention this past week than Hurricane Harvey. And yes, in a sense, the two are connected — as I will explain. PURE stands for Prospective Urban and Rural Epidemiology. I think, however, to provide a quick understanding of what the study really means, it could have meant: Poverty Undermines Reasonable Eating.

Media coverage of PURE has ranged from mildly hyperbolic to patently absurd, including the assertion that vegetables and fruits may not be good for us this week. That is pure … nonsense.

In brief, PURE was designed to look at health outcomes associated with variations in diet in countries not well represented in prior research, and across the range from high to very low socioeconomic status. A total of 18 countries — with a particular focus on the Middle East, South America, Africa, and South Asia- and about 135,000 people participated. Dietary intake was assessed with a single food frequency questionnaire at baseline.

There were two main findings that have spawned most of the mainstream media coverage, and social media buzz. The first was that, while health outcomes improved and mortality declined with higher intake of vegetables, fruits, and legumes — in multivariable analysis adjusting for other factors, that benefit “peaked” at about three servings per day. This has been widely interpreted to suggest that, at odds with conventional wisdom on the topic, more is not better with regard to vegetables, fruits, and beans.

The second finding garnering media attention was that across countries, the higher the intake of carbohydrate as a percent of calories, the higher the rates of disease and death; whereas the higher the percentage of calories from fat, the lower these rates.

Roughly 8 percent of those in the lowest intake group for vegetables, fruits, and legumes (VFL) died during the study period; whereas only 3 percent of those in the highest VFL intake group died — despite the fact that the highest VFL intake group was slightly older at baseline. Overall, and rather flagrantly, mortality was lowest in the group with the highest intake of VFL. The lowest levels of heart disease, stroke, and mortality were seen in those with the highest intake of VFL.

What, then, accounts for the strange reporting, implying that everything we’ve been told about vegetables, fruits, and beans is wrong? These benefits were “adjusted away” in multivariable models. Those people in PURE with the highest VFL intake were ALSO benefiting from less smoking, more exercise, higher education, better jobs, and quite simply- a vastly better socioeconomic existence. A multivariable model enters all of these factors to determine if a given outcome (e.g., lower death rate) can be attributed to one of them to the exclusion of the others. The exclusive, apparent benefit of VFL intake was, predictably, reduced when the linked benefits of better education, better job, and better life were included in the assessment.

This no more means that VFL was failing to provide benefit in those with more education, than that more education was failing to provide benefit in those eating more VFL. It only means that since those things happen together most of the time — it’s no longer possible to attribute a benefit to just one of them.

Unlike dietary fat, which the investigators examined in all of its various categories, carbohydrate was all “lumped” together as a single class. This produced an apparent paradox in the data: disease and death went down with more intake of vegetables, fruits, and legumes — but up with carbohydrate. What’s the paradox? Vegetables, fruits, and legumes are, mostly, carbohydrate!

What explains away the apparent paradox is that vegetable, fruit, and legume intake was apparently highest in the most affluent, most highly educated study participants — while “total carbohydrate” as a percent of calories was highest in the poorest, least educated, most disadvantaged. In those cases, carbohydrate was not a variety of highly nutritious plant foods; it was almost certainly something like white rice, and little else.

The conclusion, and attendant headlines, for PURE might have been: “very poor people with barely anything to eat get sick and die more often than affluent people with access to both ample diets, and hospitals.” One certainly understands why the media did not choose that. It is, however, true — and entirely consistent with the data.

These papers were released concurrently with the devastation in Houston, and the Gulf Coast, of Hurricane Harvey — the greatest rain event in the recorded history of the continental United States. The unprecedented rainfall is related to climate change, which in turn is monumentally influenced by global dietary choices. How appalling that the PURE findings were not merely misrepresented to the public in irresponsible reporting pertaining to human health effects, but in reporting that ignored entirely the implications of that bad dietary advice for the fate of the climate, and planet.

This week as last, whole vegetables and fruits are reliably good for you, and for the most part, the more the better. The benefits of that produce, however, do not preclude the benefits of an education, a job, and medical care — nor vice versa.

This week as last, most of the hyperbolic headlines about diet, telling us everything we thought we knew before was wrong — are pure nonsense.