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Guns, Butter, and The Burden of Proof

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In all of biomedicine, spanning clinical care, medical research, and public health practice, we subscribe to the "precautionary principle." Basically, it says: if there is a chance something can be harmful, assume it is. The burden of proof is in the other direction. You are not obligated to prove something is dangerous; you have to prove it is safe. That is precautionary, because a default assumption in that direction protects people. Or, at least, it's supposed to do so. There are inevitably gaps between the principle and practice, such as when a doctor is reckless, a vaccine tainted, or a drug rushed to market by a manufacturer disclosing only the positive data.

But our faithfulness to any principle is always imperfect because we are imperfect. That does not invalidate the principle -- it just makes it one part instructional, one part aspirational.

In clinical practice, the precautionary principle famously situates itself in the oath we physicians take: primum non nocere (first, do no harm). In research, the salience is even greater. The statistical threshold for showing a treatment does work is conventionally set much higher than the threshold for deciding it does not, in the service of avoiding a "false positive" outcome. A false positive finding suggests a treatment effect that is really just a statistical fluke, and imposes the risk of promulgating a treatment that is ineffective. There is some risk involved in virtually any treatment, just as there is a risk in crossing the street or taking a shower, so there has to be a potential benefit to justify that risk. Ineffective treatments offer no such benefit, so any risk is too great.

Now, to the matter at hand. As my title implied, this is a bit about guns and a bit about butter (well, saturated fat, actually), and the precautionary principle pertains to both.

As I am writing this, I am disappointed, but not surprised, in the immediate aftermath of Senate votes here in the U.S. defeating all of the proposed gun control measures following our latest mass casualty calamity. The measures defeated included the "obviously preposterous" idea that people deemed by the FBI unsafe to board a plane might be unsafe to buy high-capacity semi-automatic weapons.

In an entirely honest world, I suspect the arguments for the unfettered sale of guns would sound like: guys like guns, and there's lots of money to be made selling them, so those of us making money from that want to keep making money from that. Thank you, and have a nice day.

Of course, we don't live in such an honest world. Mired as we are in prevarication, subterfuge, chicanery, and ulterior motives, we get the inevitable snow job instead. We hear about defense against tyranny (from those perpetrating it), and the Constitutional right for every sociopath to have an Uzi.

But leaving such arguments aside, we might simply invoke the precautionary principle as bedrock for matters pertaining to public health, as the flow of guns clearly does. As noted above, it offers clear and relevant guidance: the burden of proof resides with those seeking to demonstrate safety/advantages, not with those concerned about harms.

Arguments that we are in any way safer and less prone to harms ranging from personal injury to governmental tyranny courtesy of ubiquitous guns are entirely hypothetical. The available evidence all goes the other way. Compared to peer countries with tighter gun controls, the U.S. has massively higher rates of gun related deaths of every description. Peer countries with tighter gun controls and democracies are as stably democratic as are we.

There are, certainly, theoretical arguments in support of the "guns for all" platform. In the unlikely scenario, for instance, that an unprovoked maniac is charging at you with a sword or battle axe from a sufficient distance and with adequate warning so that you can take out the loaded gun you happen to have in your holster or handbag and defend yourself, recourse to that gun could be a good thing. So, too, when you have an irrepressible hankering for venison. But in the overwhelming majority of real-world scenarios, including the nightclub in Orlando, guns in the hands of "good guys" or gals do not preempt carnage. As more bullets fly, they may figure in compounding it. More often still, they simply contribute to unrelated tragedies: accidental injury, accidental death, and suicide.

Global data seem to suggest quite robustly that fewer guns and bullets in circulation do not predict a greater risk of tyranny, but rather a lesser risk of mayhem. Trends in Australia ice this cake by revealing what happens when gun distribution is reduced: so, too, are all the adverse consequences of bullets flying around.

We'll leave it there. The burden of proof does not reside with those of us who see potential harm in high capacity, semi-automatic weapons in the hands of suspected domestic terrorists. The burden of proof is with the "we sell guns, so think buying more of them is a good idea" crowd. But those folks, apparently, are literate to the writing on the wall. The NRA has effectively told Congress, one imagines at gunpoint: federal funds cannot be used to study gun control. So, let's ask: who is afraid of funding research, those who want to know the truth, or those who favor the profitable bliss of ignorance and denial? If the NRA is right about the value of more guns, they should be first in line to get the data to prove it.

Anyway, moving on. The arguments for more guns are predicated on theoreticals, while ignoring the mass of real-world evidence. The arguments for the exoneration of saturated fat, or if you will, the "eat more meat, butter, cheese" platform- are exactly the same.

In the real world, none of the healthiest, longest-lived, most vital populations on the planet have a diet high in saturated fat or its prominent sources. Quite the contrary, in fact. Diets associated with optimal health outcomes over a lifetime, and generations, vary widely in total fat content, but are all plant-predominant, and low in saturated fat.

Moreover, at the level of an entire population, when a concerted effort was made to reduce intake of saturated fat in a sensible way (i.e., not replacing it with Snackwells), the result was as good or better than hoped or expected. Cardiovascular disease rates went down over 80%, and life expectancy increased by ten years. In a study of some 85,000 spanning 20 years, cardiovascular disease rates declined significantly when saturated fat calories were replaced with either whole grain calories, or unsaturated fat calories from the customary sources: nuts, seeds, olives, avocado, and fish.

And all of this is entirely consistent with a vast and diverse body of evidence encompassing methods from cell culture, to animal models, to randomized controlled trials in people.

How, then, can there even be a counter argument? As with guns, it's a case of supposition over substance. It's a case of making perfect evidence we don't have the enemy of the very good evidence we do. Because, admittedly, we don't have perfect evidence.

Consider what it would take to prove, beyond the last shadow of the last doubt, that more guns in more hands mean more, not fewer, good people in body bags. We would need several sizable populations- let's say, about 100,000 people each. These populations would need to be almost exactly matched for demographics, socioeconomics, education, vocation, temperament, mental and physical health, and of course, laws and law enforcement. We would then need to assign these populations randomly to no guns, some guns, or guns for all; these guns, or those guns. We would then need to follow them for a decade or so, and count up the body bags. The study has not been done, and I advise against holding your breath.

The same pertains to saturated fat and its prevailing sources. To know with absolute certainty that more saturated fat from the usual suspects- pastrami, cheeseburgers, ice cream, and so on- is directly responsible for more, not less, chronic disease would require the same construct. Those same, several, comparably comparable populations would need to be assigned randomly to exactly matching diets and lifestyle practices differing only in saturated fat intake from specific sources, and followed for a decade or more to compare outcomes. Then, and only then, with all other factors exactly matched, could we say with unassailable certainty what saturated fat did, or didn't do.

For whatever it's worth, the food trial is even harder than the gun trial- because inevitably, eating more of X means either eating less of Y, or simply eating more overall. Either way, you've changed something other than X. Is more meat, butter, cheese "bad" for us because it's bad for us, or because it displaces beans, lentils, nuts, seeds, and whole grains that are better for us? There is almost no way to answer that question with anything other than: who cares? If we focus on the dietary pattern that most reliably promotes vitality and longevity, that contrived detail ceases to matter.

The evidence we do have is imperfect in both cases, but the way the weight of it tips is perfectly clear. Where there are more guns in more hands, there are more bullet holes in good people. Where there is more meat, butter, and cheese in place of vegetables, fruits, whole grains, beans, lentils, nuts, and seeds- there are more years lost needlessly from life and life lost needlessly from years to chronic disease. Even more conclusively, the "eat more meat, butter, cheese" argument is on the wrong side of history, and the great imperatives of our time: climate stabilization, water use, sustainable food production, ecosystem protection, and the preservation of biodiversity.

The same liabilities attach to Coca Cola, Snackwells, and multicolored marshmallows for breakfast, of course. The notion that we must choose between an excess of sugar and an excess of saturated fat is one of the great diverting boondoggles of modern nutrition. A diet of wholesome foods in any sensible combination reliably navigates around both.

There you have it. Arguments for more guns and bullets, and arguments for more meat, butter, and cheese both put profit-driven "what ifs?" ahead of the weight of evidence. Both represent ideology ahead of epidemiology. They are shot full of holes with every reality check. Those making those arguments dismiss, disdain, or simply misconstrue the burden of proof. It is theirs.

If you have bullets or butter to peddle, it tolls for thee.


Director, Yale University Prevention Research Center; Griffin Hospital

Senior Medical Advisor,