I’ll Take Everything with a Grain of Salt


Economics is often knocked as not a “real” science.

As a discipline, I don’t doubt that modesty is justified.  The cause of the recent recession is being debated vigorously, but nothing close to a consensus backed up with clear and compelling evidence seems on the horizon.

But I tend to think that most of what we “know” is subject to great uncertainty.  In 50 years, we’ve seen optimism about life on Mars wax and wane, and despite increasing data on the planet the question is unresolved.

Perhaps with respect to health is what economics has in common with other science, namely uncertainty most clear.  Eggs were a nutritional no-no, but now they’re OK.  The truth about salt seems equally unclear.  For the rest read this from Modeled behavior. 

A while back my co-blogger Adam took a stand against the anti-salt crusaders. In general the state of knowledge about healthy behaviors is fairly low. Pretty much all of us agree that activity is generally good for the cardiovascular system. Pretty much all of us agree that trans-fatty acids are likely bad for the cardiovascular system. We all agree that you need vitamins as well as fatty acids and essential proteins to survive.

I think the agreement pretty much ends there.

Even on issues like smoking and lung cancer – which the vast majority of people consider a closed case – has smart reasonable people arguing the other side. And, admittedly it is damn hard to find a randomized controlled trial that supports the notion that smoking causes lung cancer.

I say that not to cast doubt on the connection between smoking and lung cancer but just to show how hard it is to get any result in the field behavioral health. No one is going to let you forcibly subject human beings to long term exposure to something you believe to be deadly. Thus, scientific progress requires careful inference and is mind numbingly slow.

All that having been said here is the latest on salt courtesy of Huffpost HT to Mrs. Modeled Behavior

In an analysis that set off a fierce debate over the health effects of salt, researchers said on Wednesday they had found no evidence that small cuts to salt intake reduce the risk of developing heart disease or dying prematurely.

In a systematic review published by The Cochrane Library, British scientists found that while cutting salt consumption did appear to lead to slight reductions in blood pressure, that was not translated into lower death or heart disease risk.

The researchers said they suspected the trials conducted so far were not big enough to show any benefits to heart health, and called for large-scale studies to be carried out soon.

Perhaps larger scale studies will yield results. However, the same argument was made about fat and when the newer, larger scale study was done it came out with ziltch. The response was that a study that large could not possibly have the controls necessary to find an effect.

None of this is to say that there isn’t an effect in either case but we should be clear that the evidence is sorely lacking and that public health authorities have been bordering on dishonest about these issues.

I am always one to be skeptical about conspiracy theories but in this case I think the motivation and method used to promote the conspiracy are clear: people thought they were saving lives. Its hard to get people to band together into some giant united effort at deception but the idea that you are saving the world is one of the few things that can do it.

Unfortunately that type of zeal blinds folks to the data.

The salt case was riddled with issues from the start. Not least of which was that there was no real theory here. It is clear that salt could increase blood volume and thereby temporarily raise blood pressure. However, proponents of the salt theory were suggesting that permanent hypertension would result and from the start it was never exactly clear why this should be the case.

This happens shockingly often in medicine and health.

Filed under: Health Care

The Latest on Salt: Cochrane Reviews Finds Little to No Harm
Karl Smith
Wed, 06 Jul 2011 22:25:07 GMT

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2 responses to “I’ll Take Everything with a Grain of Salt

  1. Amen to the title of this post, Bruce. Did you see the article on Joanne Slavin, an expert that was on the panel for the new dietary guidelines?

    http://livinlavidalowcarb.com/blog/2010-dietary-guidelines-committee-member-joanne-slavin-there-is-no-scientific-basis-for-the-u-s-dietary-guidelines/10986

    I for one am sick of hearing about the obesity epidemic, perhaps b/c no one in my immediate nor extended family is obese so I can’t relate. But I sure suspect that, if there is an epidemic, it’s more likely caused by the slow breakdown of the concept of individual responsibility, rather than “food deserts.”

    cheers bud.

    • Well interesting. Mostly its hard to know what to believe on what’s a good diet.

      I’m a little pudgy myself. Check out me as a kid a post or two down. I’ve moved up and down in weight over time.

      Maybe its good medical care. Seems paradoxical doesn’t it?

      Well, economists love to theorize even if we’re wrong, so try this on for size.

      If indeed medical care has improved this could (at least apparently) make the country appear fatter in two ways.

      First, heavier people who might have died 20 years ago live longer and add their great weight to our stats. It’s not that skinny people are getting fat. Its that fat people are living. Actually improved care for diabetics could contribute to this, and maybe diabetics living longer could account for more diabetes as well, not that more people are contracting it.

      Second, if the medical consequences of being fat aren’t as dangerous as they used to be, then people may make less effort to avoid getting fat. This would be similar to what’s been called the Peltzman effect (for economist Sam Peltzman). The Peltzman effect is that if people have seat belts in cars, they may actually drive more recklessly because the risk is less. Highway deaths might decrease less than the use of seatbelts would lead you to expect. In other words, incentive matter and the incentive to safety is less. Same might apply if people are less afraid of obesity related disease, and people would get fatter. Maybe it saying the same as you on breakdown of responsibility.

      I don’t take this idea very seriously, it was largely off the cuff, but I enjoyed dreaming it up.

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