Download 2016-06-24 Burden of Proof

Preventive Medicine Column
June 24, 2016
Public Health & The Burden of Proof
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.
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.
As I am writing this, I am disappointed, but not surprised, in the immediate aftermath of Senate votes
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.
We might 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. 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.
The burden of proof does not reside with those of us who see potential harm in high capacity, semiautomatic weapons in the hands of suspected domestic terrorists. The burden of proof is with those selling
guns to prove the safety benefits at the population level.
This column, though, is about matters of public health importance, not just guns. It is just as much
about butter. The arguments for more guns are predicated on theoreticals, while ignoring the mass of realworld 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. When a concerted effort was made to reduce intake of saturated fat in a sensible way
(i.e., not replacing it with Snackwells) in Finland, 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.
The evidence we have about the net effects of more guns and more saturated fat is imperfect, 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.
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. Those making those arguments dismiss, disdain, or
simply misconstrue the burden of proof. It belongs to them.
-fin Dr. David L. Katz;www.davidkatzmd.com; author, Disease Proof; founder, True Health Initiative